[safe/jmp/linux-2.6] / arch / x86 / xen / enlighten.c

/*
 * Core of Xen paravirt_ops implementation.
 *
 * This file contains the xen_paravirt_ops structure itself, and the
 * implementations for:
 * - privileged instructions
 * - interrupt flags
 * - segment operations
 * - booting and setup
 *
 * Jeremy Fitzhardinge <jeremy@xensource.com>, XenSource Inc, 2007
 */

#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/smp.h>
#include <linux/preempt.h>
#include <linux/hardirq.h>
#include <linux/percpu.h>
#include <linux/delay.h>
#include <linux/start_kernel.h>
#include <linux/sched.h>
#include <linux/bootmem.h>
#include <linux/module.h>
#include <linux/mm.h>
#include <linux/page-flags.h>
#include <linux/highmem.h>
#include <linux/console.h>

#include <xen/interface/xen.h>
#include <xen/interface/physdev.h>
#include <xen/interface/vcpu.h>
#include <xen/features.h>
#include <xen/page.h>
#include <xen/hvc-console.h>

#include <asm/paravirt.h>
#include <asm/page.h>
#include <asm/xen/hypercall.h>
#include <asm/xen/hypervisor.h>
#include <asm/fixmap.h>
#include <asm/processor.h>
#include <asm/msr-index.h>
#include <asm/setup.h>
#include <asm/desc.h>
#include <asm/pgtable.h>
#include <asm/tlbflush.h>
#include <asm/reboot.h>

#include "xen-ops.h"
#include "mmu.h"
#include "multicalls.h"

EXPORT_SYMBOL_GPL(hypercall_page);

DEFINE_PER_CPU(struct vcpu_info *, xen_vcpu);
DEFINE_PER_CPU(struct vcpu_info, xen_vcpu_info);

/*
 * Identity map, in addition to plain kernel map.  This needs to be
 * large enough to allocate page table pages to allocate the rest.
 * Each page can map 2MB.
 */
static pte_t level1_ident_pgt[PTRS_PER_PTE * 4] __page_aligned_bss;

#ifdef CONFIG_X86_64
/* l3 pud for userspace vsyscall mapping */
static pud_t level3_user_vsyscall[PTRS_PER_PUD] __page_aligned_bss;
#endif /* CONFIG_X86_64 */

/*
 * Note about cr3 (pagetable base) values:
 *
 * xen_cr3 contains the current logical cr3 value; it contains the
 * last set cr3.  This may not be the current effective cr3, because
 * its update may be being lazily deferred.  However, a vcpu looking
 * at its own cr3 can use this value knowing that it everything will
 * be self-consistent.
 *
 * xen_current_cr3 contains the actual vcpu cr3; it is set once the
 * hypercall to set the vcpu cr3 is complete (so it may be a little
 * out of date, but it will never be set early).  If one vcpu is
 * looking at another vcpu's cr3 value, it should use this variable.
 */
DEFINE_PER_CPU(unsigned long, xen_cr3);  /* cr3 stored as physaddr */
DEFINE_PER_CPU(unsigned long, xen_current_cr3);  /* actual vcpu cr3 */

struct start_info *xen_start_info;
EXPORT_SYMBOL_GPL(xen_start_info);

struct shared_info xen_dummy_shared_info;

/*
 * Point at some empty memory to start with. We map the real shared_info
 * page as soon as fixmap is up and running.
 */
struct shared_info *HYPERVISOR_shared_info = (void *)&xen_dummy_shared_info;

/*
 * Flag to determine whether vcpu info placement is available on all
 * VCPUs.  We assume it is to start with, and then set it to zero on
 * the first failure.  This is because it can succeed on some VCPUs
 * and not others, since it can involve hypervisor memory allocation,
 * or because the guest failed to guarantee all the appropriate
 * constraints on all VCPUs (ie buffer can't cross a page boundary).
 *
 * Note that any particular CPU may be using a placed vcpu structure,
 * but we can only optimise if the all are.
 *
 * 0: not available, 1: available
 */
static int have_vcpu_info_placement = 1;

static void xen_vcpu_setup(int cpu)
{
        struct vcpu_register_vcpu_info info;
        int err;
        struct vcpu_info *vcpup;

        BUG_ON(HYPERVISOR_shared_info == &xen_dummy_shared_info);
        per_cpu(xen_vcpu, cpu) = &HYPERVISOR_shared_info->vcpu_info[cpu];

        if (!have_vcpu_info_placement)
                return;         /* already tested, not available */

        vcpup = &per_cpu(xen_vcpu_info, cpu);

        info.mfn = virt_to_mfn(vcpup);
        info.offset = offset_in_page(vcpup);

        printk(KERN_DEBUG "trying to map vcpu_info %d at %p, mfn %llx, offset %d\n",
               cpu, vcpup, info.mfn, info.offset);

        /* Check to see if the hypervisor will put the vcpu_info
           structure where we want it, which allows direct access via
           a percpu-variable. */
        err = HYPERVISOR_vcpu_op(VCPUOP_register_vcpu_info, cpu, &info);

        if (err) {
                printk(KERN_DEBUG "register_vcpu_info failed: err=%d\n", err);
                have_vcpu_info_placement = 0;
        } else {
                /* This cpu is using the registered vcpu info, even if
                   later ones fail to. */
                per_cpu(xen_vcpu, cpu) = vcpup;

                printk(KERN_DEBUG "cpu %d using vcpu_info at %p\n",
                       cpu, vcpup);
        }
}

/*
 * On restore, set the vcpu placement up again.
 * If it fails, then we're in a bad state, since
 * we can't back out from using it...
 */
void xen_vcpu_restore(void)
{
        if (have_vcpu_info_placement) {
                int cpu;

                for_each_online_cpu(cpu) {
                        bool other_cpu = (cpu != smp_processor_id());

                        if (other_cpu &&
                            HYPERVISOR_vcpu_op(VCPUOP_down, cpu, NULL))
                                BUG();

                        xen_vcpu_setup(cpu);

                        if (other_cpu &&
                            HYPERVISOR_vcpu_op(VCPUOP_up, cpu, NULL))
                                BUG();
                }

                BUG_ON(!have_vcpu_info_placement);
        }
}

static void __init xen_banner(void)
{
        unsigned version = HYPERVISOR_xen_version(XENVER_version, NULL);
        struct xen_extraversion extra;
        HYPERVISOR_xen_version(XENVER_extraversion, &extra);

        printk(KERN_INFO "Booting paravirtualized kernel on %s\n",
               pv_info.name);
        printk(KERN_INFO "Xen version: %d.%d%s%s\n",
               version >> 16, version & 0xffff, extra.extraversion,
               xen_feature(XENFEAT_mmu_pt_update_preserve_ad) ? " (preserve-AD)" : "");
}

static void xen_cpuid(unsigned int *ax, unsigned int *bx,
                      unsigned int *cx, unsigned int *dx)
{
        unsigned maskedx = ~0;

        /*
         * Mask out inconvenient features, to try and disable as many
         * unsupported kernel subsystems as possible.
         */
        if (*ax == 1)
                maskedx = ~((1 << X86_FEATURE_APIC) |  /* disable APIC */
                            (1 << X86_FEATURE_ACPI) |  /* disable ACPI */
                            (1 << X86_FEATURE_MCE)  |  /* disable MCE */
                            (1 << X86_FEATURE_MCA)  |  /* disable MCA */
                            (1 << X86_FEATURE_ACC));   /* thermal monitoring */

        asm(XEN_EMULATE_PREFIX "cpuid"
                : "=a" (*ax),
                  "=b" (*bx),
                  "=c" (*cx),
                  "=d" (*dx)
                : "0" (*ax), "2" (*cx));
        *dx &= maskedx;
}

static void xen_set_debugreg(int reg, unsigned long val)
{
        HYPERVISOR_set_debugreg(reg, val);
}

static unsigned long xen_get_debugreg(int reg)
{
        return HYPERVISOR_get_debugreg(reg);
}

static void xen_leave_lazy(void)
{
        paravirt_leave_lazy(paravirt_get_lazy_mode());
        xen_mc_flush();
}

static unsigned long xen_store_tr(void)
{
        return 0;
}

/*
 * Set the page permissions for a particular virtual address.  If the
 * address is a vmalloc mapping (or other non-linear mapping), then
 * find the linear mapping of the page and also set its protections to
 * match.
 */
static void set_aliased_prot(void *v, pgprot_t prot)
{
        int level;
        pte_t *ptep;
        pte_t pte;
        unsigned long pfn;
        struct page *page;

        ptep = lookup_address((unsigned long)v, &level);
        BUG_ON(ptep == NULL);

        pfn = pte_pfn(*ptep);
        page = pfn_to_page(pfn);

        pte = pfn_pte(pfn, prot);

        if (HYPERVISOR_update_va_mapping((unsigned long)v, pte, 0))
                BUG();

        if (!PageHighMem(page)) {
                void *av = __va(PFN_PHYS(pfn));

                if (av != v)
                        if (HYPERVISOR_update_va_mapping((unsigned long)av, pte, 0))
                                BUG();
        } else
                kmap_flush_unused();
}

static void xen_alloc_ldt(struct desc_struct *ldt, unsigned entries)
{
        const unsigned entries_per_page = PAGE_SIZE / LDT_ENTRY_SIZE;
        int i;

        for(i = 0; i < entries; i += entries_per_page)
                set_aliased_prot(ldt + i, PAGE_KERNEL_RO);
}

static void xen_free_ldt(struct desc_struct *ldt, unsigned entries)
{
        const unsigned entries_per_page = PAGE_SIZE / LDT_ENTRY_SIZE;
        int i;

        for(i = 0; i < entries; i += entries_per_page)
                set_aliased_prot(ldt + i, PAGE_KERNEL);
}

static void xen_set_ldt(const void *addr, unsigned entries)
{
        struct mmuext_op *op;
        struct multicall_space mcs = xen_mc_entry(sizeof(*op));

        op = mcs.args;
        op->cmd = MMUEXT_SET_LDT;
        op->arg1.linear_addr = (unsigned long)addr;
        op->arg2.nr_ents = entries;

        MULTI_mmuext_op(mcs.mc, op, 1, NULL, DOMID_SELF);

        xen_mc_issue(PARAVIRT_LAZY_CPU);
}

static void xen_load_gdt(const struct desc_ptr *dtr)
{
        unsigned long *frames;
        unsigned long va = dtr->address;
        unsigned int size = dtr->size + 1;
        unsigned pages = (size + PAGE_SIZE - 1) / PAGE_SIZE;
        int f;
        struct multicall_space mcs;

        /* A GDT can be up to 64k in size, which corresponds to 8192
           8-byte entries, or 16 4k pages.. */

        BUG_ON(size > 65536);
        BUG_ON(va & ~PAGE_MASK);

        mcs = xen_mc_entry(sizeof(*frames) * pages);
        frames = mcs.args;

        for (f = 0; va < dtr->address + size; va += PAGE_SIZE, f++) {
                frames[f] = virt_to_mfn(va);
                make_lowmem_page_readonly((void *)va);
        }

        MULTI_set_gdt(mcs.mc, frames, size / sizeof(struct desc_struct));

        xen_mc_issue(PARAVIRT_LAZY_CPU);
}

static void load_TLS_descriptor(struct thread_struct *t,
                                unsigned int cpu, unsigned int i)
{
        struct desc_struct *gdt = get_cpu_gdt_table(cpu);
        xmaddr_t maddr = virt_to_machine(&gdt[GDT_ENTRY_TLS_MIN+i]);
        struct multicall_space mc = __xen_mc_entry(0);

        MULTI_update_descriptor(mc.mc, maddr.maddr, t->tls_array[i]);
}

static void xen_load_tls(struct thread_struct *t, unsigned int cpu)
{
        /*
         * XXX sleazy hack: If we're being called in a lazy-cpu zone,
         * it means we're in a context switch, and %gs has just been
         * saved.  This means we can zero it out to prevent faults on
         * exit from the hypervisor if the next process has no %gs.
         * Either way, it has been saved, and the new value will get
         * loaded properly.  This will go away as soon as Xen has been
         * modified to not save/restore %gs for normal hypercalls.
         *
         * On x86_64, this hack is not used for %gs, because gs points
         * to KERNEL_GS_BASE (and uses it for PDA references), so we
         * must not zero %gs on x86_64
         *
         * For x86_64, we need to zero %fs, otherwise we may get an
         * exception between the new %fs descriptor being loaded and
         * %fs being effectively cleared at __switch_to().
         */
        if (paravirt_get_lazy_mode() == PARAVIRT_LAZY_CPU) {
#ifdef CONFIG_X86_32
                loadsegment(gs, 0);
#else
                loadsegment(fs, 0);
#endif
        }

        xen_mc_batch();

        load_TLS_descriptor(t, cpu, 0);
        load_TLS_descriptor(t, cpu, 1);
        load_TLS_descriptor(t, cpu, 2);

        xen_mc_issue(PARAVIRT_LAZY_CPU);
}

#ifdef CONFIG_X86_64
static void xen_load_gs_index(unsigned int idx)
{
        if (HYPERVISOR_set_segment_base(SEGBASE_GS_USER_SEL, idx))
                BUG();
}
#endif

static void xen_write_ldt_entry(struct desc_struct *dt, int entrynum,
                                const void *ptr)
{
        xmaddr_t mach_lp = arbitrary_virt_to_machine(&dt[entrynum]);
        u64 entry = *(u64 *)ptr;

        preempt_disable();

        xen_mc_flush();
        if (HYPERVISOR_update_descriptor(mach_lp.maddr, entry))
                BUG();

        preempt_enable();
}

static int cvt_gate_to_trap(int vector, const gate_desc *val,
                            struct trap_info *info)
{
        if (val->type != 0xf && val->type != 0xe)
                return 0;

        info->vector = vector;
        info->address = gate_offset(*val);
        info->cs = gate_segment(*val);
        info->flags = val->dpl;
        /* interrupt gates clear IF */
        if (val->type == 0xe)
                info->flags |= 4;

        return 1;
}

/* Locations of each CPU's IDT */
static DEFINE_PER_CPU(struct desc_ptr, idt_desc);

/* Set an IDT entry.  If the entry is part of the current IDT, then
   also update Xen. */
static void xen_write_idt_entry(gate_desc *dt, int entrynum, const gate_desc *g)
{
        unsigned long p = (unsigned long)&dt[entrynum];
        unsigned long start, end;

        preempt_disable();

        start = __get_cpu_var(idt_desc).address;
        end = start + __get_cpu_var(idt_desc).size + 1;

        xen_mc_flush();

        native_write_idt_entry(dt, entrynum, g);

        if (p >= start && (p + 8) <= end) {
                struct trap_info info[2];

                info[1].address = 0;

                if (cvt_gate_to_trap(entrynum, g, &info[0]))
                        if (HYPERVISOR_set_trap_table(info))
                                BUG();
        }

        preempt_enable();
}

static void xen_convert_trap_info(const struct desc_ptr *desc,
                                  struct trap_info *traps)
{
        unsigned in, out, count;

        count = (desc->size+1) / sizeof(gate_desc);
        BUG_ON(count > 256);

        for (in = out = 0; in < count; in++) {
                gate_desc *entry = (gate_desc*)(desc->address) + in;

                if (cvt_gate_to_trap(in, entry, &traps[out]))
                        out++;
        }
        traps[out].address = 0;
}

void xen_copy_trap_info(struct trap_info *traps)
{
        const struct desc_ptr *desc = &__get_cpu_var(idt_desc);

        xen_convert_trap_info(desc, traps);
}

/* Load a new IDT into Xen.  In principle this can be per-CPU, so we
   hold a spinlock to protect the static traps[] array (static because
   it avoids allocation, and saves stack space). */
static void xen_load_idt(const struct desc_ptr *desc)
{
        static DEFINE_SPINLOCK(lock);
        static struct trap_info traps[257];

        spin_lock(&lock);

        __get_cpu_var(idt_desc) = *desc;

        xen_convert_trap_info(desc, traps);

        xen_mc_flush();
        if (HYPERVISOR_set_trap_table(traps))
                BUG();

        spin_unlock(&lock);
}

/* Write a GDT descriptor entry.  Ignore LDT descriptors, since
   they're handled differently. */
static void xen_write_gdt_entry(struct desc_struct *dt, int entry,
                                const void *desc, int type)
{
        preempt_disable();

        switch (type) {
        case DESC_LDT:
        case DESC_TSS:
                /* ignore */
                break;

        default: {
                xmaddr_t maddr = virt_to_machine(&dt[entry]);

                xen_mc_flush();
                if (HYPERVISOR_update_descriptor(maddr.maddr, *(u64 *)desc))
                        BUG();
        }

        }

        preempt_enable();
}

static void xen_load_sp0(struct tss_struct *tss,
                         struct thread_struct *thread)
{
        struct multicall_space mcs = xen_mc_entry(0);
        MULTI_stack_switch(mcs.mc, __KERNEL_DS, thread->sp0);
        xen_mc_issue(PARAVIRT_LAZY_CPU);
}

static void xen_set_iopl_mask(unsigned mask)
{
        struct physdev_set_iopl set_iopl;

        /* Force the change at ring 0. */
        set_iopl.iopl = (mask == 0) ? 1 : (mask >> 12) & 3;
        HYPERVISOR_physdev_op(PHYSDEVOP_set_iopl, &set_iopl);
}

static void xen_io_delay(void)
{
}

#ifdef CONFIG_X86_LOCAL_APIC
static u32 xen_apic_read(unsigned long reg)
{
        return 0;
}

static void xen_apic_write(unsigned long reg, u32 val)
{
        /* Warn to see if there's any stray references */
        WARN_ON(1);
}
#endif

static void xen_flush_tlb(void)
{
        struct mmuext_op *op;
        struct multicall_space mcs;

        preempt_disable();

        mcs = xen_mc_entry(sizeof(*op));

        op = mcs.args;
        op->cmd = MMUEXT_TLB_FLUSH_LOCAL;
        MULTI_mmuext_op(mcs.mc, op, 1, NULL, DOMID_SELF);

        xen_mc_issue(PARAVIRT_LAZY_MMU);

        preempt_enable();
}

static void xen_flush_tlb_single(unsigned long addr)
{
        struct mmuext_op *op;
        struct multicall_space mcs;

        preempt_disable();

        mcs = xen_mc_entry(sizeof(*op));
        op = mcs.args;
        op->cmd = MMUEXT_INVLPG_LOCAL;
        op->arg1.linear_addr = addr & PAGE_MASK;
        MULTI_mmuext_op(mcs.mc, op, 1, NULL, DOMID_SELF);

        xen_mc_issue(PARAVIRT_LAZY_MMU);

        preempt_enable();
}

static void xen_flush_tlb_others(const cpumask_t *cpus, struct mm_struct *mm,
                                 unsigned long va)
{
        struct {
                struct mmuext_op op;
                cpumask_t mask;
        } *args;
        cpumask_t cpumask = *cpus;
        struct multicall_space mcs;

        /*
         * A couple of (to be removed) sanity checks:
         *
         * - current CPU must not be in mask
         * - mask must exist :)
         */
        BUG_ON(cpus_empty(cpumask));
        BUG_ON(cpu_isset(smp_processor_id(), cpumask));
        BUG_ON(!mm);

        /* If a CPU which we ran on has gone down, OK. */
        cpus_and(cpumask, cpumask, cpu_online_map);
        if (cpus_empty(cpumask))
                return;

        mcs = xen_mc_entry(sizeof(*args));
        args = mcs.args;
        args->mask = cpumask;
        args->op.arg2.vcpumask = &args->mask;

        if (va == TLB_FLUSH_ALL) {
                args->op.cmd = MMUEXT_TLB_FLUSH_MULTI;
        } else {
                args->op.cmd = MMUEXT_INVLPG_MULTI;
                args->op.arg1.linear_addr = va;
        }

        MULTI_mmuext_op(mcs.mc, &args->op, 1, NULL, DOMID_SELF);

        xen_mc_issue(PARAVIRT_LAZY_MMU);
}

static void xen_clts(void)
{
        struct multicall_space mcs;

        mcs = xen_mc_entry(0);

        MULTI_fpu_taskswitch(mcs.mc, 0);

        xen_mc_issue(PARAVIRT_LAZY_CPU);
}

static void xen_write_cr0(unsigned long cr0)
{
        struct multicall_space mcs;

        /* Only pay attention to cr0.TS; everything else is
           ignored. */
        mcs = xen_mc_entry(0);

        MULTI_fpu_taskswitch(mcs.mc, (cr0 & X86_CR0_TS) != 0);

        xen_mc_issue(PARAVIRT_LAZY_CPU);
}

static void xen_write_cr2(unsigned long cr2)
{
        x86_read_percpu(xen_vcpu)->arch.cr2 = cr2;
}

static unsigned long xen_read_cr2(void)
{
        return x86_read_percpu(xen_vcpu)->arch.cr2;
}

static unsigned long xen_read_cr2_direct(void)
{
        return x86_read_percpu(xen_vcpu_info.arch.cr2);
}

static void xen_write_cr4(unsigned long cr4)
{
        cr4 &= ~X86_CR4_PGE;
        cr4 &= ~X86_CR4_PSE;

        native_write_cr4(cr4);
}

static unsigned long xen_read_cr3(void)
{
        return x86_read_percpu(xen_cr3);
}

static void set_current_cr3(void *v)
{
        x86_write_percpu(xen_current_cr3, (unsigned long)v);
}

static void __xen_write_cr3(bool kernel, unsigned long cr3)
{
        struct mmuext_op *op;
        struct multicall_space mcs;
        unsigned long mfn;

        if (cr3)
                mfn = pfn_to_mfn(PFN_DOWN(cr3));
        else
                mfn = 0;

        WARN_ON(mfn == 0 && kernel);

        mcs = __xen_mc_entry(sizeof(*op));

        op = mcs.args;
        op->cmd = kernel ? MMUEXT_NEW_BASEPTR : MMUEXT_NEW_USER_BASEPTR;
        op->arg1.mfn = mfn;

        MULTI_mmuext_op(mcs.mc, op, 1, NULL, DOMID_SELF);

        if (kernel) {
                x86_write_percpu(xen_cr3, cr3);

                /* Update xen_current_cr3 once the batch has actually
                   been submitted. */
                xen_mc_callback(set_current_cr3, (void *)cr3);
        }
}

static void xen_write_cr3(unsigned long cr3)
{
        BUG_ON(preemptible());

        xen_mc_batch();  /* disables interrupts */

        /* Update while interrupts are disabled, so its atomic with
           respect to ipis */
        x86_write_percpu(xen_cr3, cr3);

        __xen_write_cr3(true, cr3);

#ifdef CONFIG_X86_64
        {
                pgd_t *user_pgd = xen_get_user_pgd(__va(cr3));
                if (user_pgd)
                        __xen_write_cr3(false, __pa(user_pgd));
                else
                        __xen_write_cr3(false, 0);
        }
#endif

        xen_mc_issue(PARAVIRT_LAZY_CPU);  /* interrupts restored */
}

static int xen_write_msr_safe(unsigned int msr, unsigned low, unsigned high)
{
        int ret;

        ret = 0;

        switch(msr) {
#ifdef CONFIG_X86_64
                unsigned which;
                u64 base;

        case MSR_FS_BASE:               which = SEGBASE_FS; goto set;
        case MSR_KERNEL_GS_BASE:        which = SEGBASE_GS_USER; goto set;
        case MSR_GS_BASE:               which = SEGBASE_GS_KERNEL; goto set;

        set:
                base = ((u64)high << 32) | low;
                if (HYPERVISOR_set_segment_base(which, base) != 0)
                        ret = -EFAULT;
                break;
#endif

        case MSR_STAR:
        case MSR_CSTAR:
        case MSR_LSTAR:
        case MSR_SYSCALL_MASK:
        case MSR_IA32_SYSENTER_CS:
        case MSR_IA32_SYSENTER_ESP:
        case MSR_IA32_SYSENTER_EIP:
                /* Fast syscall setup is all done in hypercalls, so
                   these are all ignored.  Stub them out here to stop
                   Xen console noise. */
                break;

        default:
                ret = native_write_msr_safe(msr, low, high);
        }

        return ret;
}

/* Early in boot, while setting up the initial pagetable, assume
   everything is pinned. */
static __init void xen_alloc_pte_init(struct mm_struct *mm, u32 pfn)
{
#ifdef CONFIG_FLATMEM
        BUG_ON(mem_map);        /* should only be used early */
#endif
        make_lowmem_page_readonly(__va(PFN_PHYS(pfn)));
}

/* Early release_pte assumes that all pts are pinned, since there's
   only init_mm and anything attached to that is pinned. */
static void xen_release_pte_init(u32 pfn)
{
        make_lowmem_page_readwrite(__va(PFN_PHYS(pfn)));
}

static void pin_pagetable_pfn(unsigned cmd, unsigned long pfn)
{
        struct mmuext_op op;
        op.cmd = cmd;
        op.arg1.mfn = pfn_to_mfn(pfn);
        if (HYPERVISOR_mmuext_op(&op, 1, NULL, DOMID_SELF))
                BUG();
}

/* This needs to make sure the new pte page is pinned iff its being
   attached to a pinned pagetable. */
static void xen_alloc_ptpage(struct mm_struct *mm, u32 pfn, unsigned level)
{
        struct page *page = pfn_to_page(pfn);

        if (PagePinned(virt_to_page(mm->pgd))) {
                SetPagePinned(page);

                if (!PageHighMem(page)) {
                        make_lowmem_page_readonly(__va(PFN_PHYS((unsigned long)pfn)));
                        if (level == PT_PTE)
                                pin_pagetable_pfn(MMUEXT_PIN_L1_TABLE, pfn);
                } else
                        /* make sure there are no stray mappings of
                           this page */
                        kmap_flush_unused();
        }
}

static void xen_alloc_pte(struct mm_struct *mm, u32 pfn)
{
        xen_alloc_ptpage(mm, pfn, PT_PTE);
}

static void xen_alloc_pmd(struct mm_struct *mm, u32 pfn)
{
        xen_alloc_ptpage(mm, pfn, PT_PMD);
}

static int xen_pgd_alloc(struct mm_struct *mm)
{
        pgd_t *pgd = mm->pgd;
        int ret = 0;

        BUG_ON(PagePinned(virt_to_page(pgd)));

#ifdef CONFIG_X86_64
        {
                struct page *page = virt_to_page(pgd);
                pgd_t *user_pgd;

                BUG_ON(page->private != 0);

                ret = -ENOMEM;

                user_pgd = (pgd_t *)__get_free_page(GFP_KERNEL | __GFP_ZERO);
                page->private = (unsigned long)user_pgd;

                if (user_pgd != NULL) {
                        user_pgd[pgd_index(VSYSCALL_START)] =
                                __pgd(__pa(level3_user_vsyscall) | _PAGE_TABLE);
                        ret = 0;
                }

                BUG_ON(PagePinned(virt_to_page(xen_get_user_pgd(pgd))));
        }
#endif

        return ret;
}

static void xen_pgd_free(struct mm_struct *mm, pgd_t *pgd)
{
#ifdef CONFIG_X86_64
        pgd_t *user_pgd = xen_get_user_pgd(pgd);

        if (user_pgd)
                free_page((unsigned long)user_pgd);
#endif
}

/* This should never happen until we're OK to use struct page */
static void xen_release_ptpage(u32 pfn, unsigned level)
{
        struct page *page = pfn_to_page(pfn);

        if (PagePinned(page)) {
                if (!PageHighMem(page)) {
                        if (level == PT_PTE)
                                pin_pagetable_pfn(MMUEXT_UNPIN_TABLE, pfn);
                        make_lowmem_page_readwrite(__va(PFN_PHYS(pfn)));
                }
                ClearPagePinned(page);
        }
}

static void xen_release_pte(u32 pfn)
{
        xen_release_ptpage(pfn, PT_PTE);
}

static void xen_release_pmd(u32 pfn)
{
        xen_release_ptpage(pfn, PT_PMD);
}

#if PAGETABLE_LEVELS == 4
static void xen_alloc_pud(struct mm_struct *mm, u32 pfn)
{
        xen_alloc_ptpage(mm, pfn, PT_PUD);
}

static void xen_release_pud(u32 pfn)
{
        xen_release_ptpage(pfn, PT_PUD);
}
#endif

#ifdef CONFIG_HIGHPTE
static void *xen_kmap_atomic_pte(struct page *page, enum km_type type)
{
        pgprot_t prot = PAGE_KERNEL;

        if (PagePinned(page))
                prot = PAGE_KERNEL_RO;

        if (0 && PageHighMem(page))
                printk("mapping highpte %lx type %d prot %s\n",
                       page_to_pfn(page), type,
                       (unsigned long)pgprot_val(prot) & _PAGE_RW ? "WRITE" : "READ");

        return kmap_atomic_prot(page, type, prot);
}
#endif

static __init pte_t mask_rw_pte(pte_t *ptep, pte_t pte)
{
        /* If there's an existing pte, then don't allow _PAGE_RW to be set */
        if (pte_val_ma(*ptep) & _PAGE_PRESENT)
                pte = __pte_ma(((pte_val_ma(*ptep) & _PAGE_RW) | ~_PAGE_RW) &
                               pte_val_ma(pte));

        return pte;
}

/* Init-time set_pte while constructing initial pagetables, which
   doesn't allow RO pagetable pages to be remapped RW */
static __init void xen_set_pte_init(pte_t *ptep, pte_t pte)
{
        pte = mask_rw_pte(ptep, pte);

        xen_set_pte(ptep, pte);
}

static __init void xen_pagetable_setup_start(pgd_t *base)
{
}

void xen_setup_shared_info(void)
{
        if (!xen_feature(XENFEAT_auto_translated_physmap)) {
                set_fixmap(FIX_PARAVIRT_BOOTMAP,
                           xen_start_info->shared_info);

                HYPERVISOR_shared_info =
                        (struct shared_info *)fix_to_virt(FIX_PARAVIRT_BOOTMAP);
        } else
                HYPERVISOR_shared_info =
                        (struct shared_info *)__va(xen_start_info->shared_info);

#ifndef CONFIG_SMP
        /* In UP this is as good a place as any to set up shared info */
        xen_setup_vcpu_info_placement();
#endif

        xen_setup_mfn_list_list();
}

static __init void xen_pagetable_setup_done(pgd_t *base)
{
        xen_setup_shared_info();
}

static __init void xen_post_allocator_init(void)
{
        pv_mmu_ops.set_pte = xen_set_pte;
        pv_mmu_ops.set_pmd = xen_set_pmd;
        pv_mmu_ops.set_pud = xen_set_pud;
#if PAGETABLE_LEVELS == 4
        pv_mmu_ops.set_pgd = xen_set_pgd;
#endif

        /* This will work as long as patching hasn't happened yet
           (which it hasn't) */
        pv_mmu_ops.alloc_pte = xen_alloc_pte;
        pv_mmu_ops.alloc_pmd = xen_alloc_pmd;
        pv_mmu_ops.release_pte = xen_release_pte;
        pv_mmu_ops.release_pmd = xen_release_pmd;
#if PAGETABLE_LEVELS == 4
        pv_mmu_ops.alloc_pud = xen_alloc_pud;
        pv_mmu_ops.release_pud = xen_release_pud;
#endif

#ifdef CONFIG_X86_64
        SetPagePinned(virt_to_page(level3_user_vsyscall));
#endif
        xen_mark_init_mm_pinned();
}

/* This is called once we have the cpu_possible_map */
void xen_setup_vcpu_info_placement(void)
{
        int cpu;

        for_each_possible_cpu(cpu)
                xen_vcpu_setup(cpu);

        /* xen_vcpu_setup managed to place the vcpu_info within the
           percpu area for all cpus, so make use of it */
#ifdef CONFIG_X86_32
        if (have_vcpu_info_placement) {
                printk(KERN_INFO "Xen: using vcpu_info placement\n");

                pv_irq_ops.save_fl = xen_save_fl_direct;
                pv_irq_ops.restore_fl = xen_restore_fl_direct;
                pv_irq_ops.irq_disable = xen_irq_disable_direct;
                pv_irq_ops.irq_enable = xen_irq_enable_direct;
                pv_mmu_ops.read_cr2 = xen_read_cr2_direct;
        }
#endif
}

static unsigned xen_patch(u8 type, u16 clobbers, void *insnbuf,
                          unsigned long addr, unsigned len)
{
        char *start, *end, *reloc;
        unsigned ret;

        start = end = reloc = NULL;

#define SITE(op, x)                                                     \
        case PARAVIRT_PATCH(op.x):                                      \
        if (have_vcpu_info_placement) {                                 \
                start = (char *)xen_##x##_direct;                       \
                end = xen_##x##_direct_end;                             \
                reloc = xen_##x##_direct_reloc;                         \
        }                                                               \
        goto patch_site

        switch (type) {
#ifdef CONFIG_X86_32
                SITE(pv_irq_ops, irq_enable);
                SITE(pv_irq_ops, irq_disable);
                SITE(pv_irq_ops, save_fl);
                SITE(pv_irq_ops, restore_fl);
#endif /* CONFIG_X86_32 */
#undef SITE

        patch_site:
                if (start == NULL || (end-start) > len)
                        goto default_patch;

                ret = paravirt_patch_insns(insnbuf, len, start, end);

                /* Note: because reloc is assigned from something that
                   appears to be an array, gcc assumes it's non-null,
                   but doesn't know its relationship with start and
                   end. */
                if (reloc > start && reloc < end) {
                        int reloc_off = reloc - start;
                        long *relocp = (long *)(insnbuf + reloc_off);
                        long delta = start - (char *)addr;

                        *relocp += delta;
                }
                break;

        default_patch:
        default:
                ret = paravirt_patch_default(type, clobbers, insnbuf,
                                             addr, len);
                break;
        }

        return ret;
}

static void xen_set_fixmap(unsigned idx, unsigned long phys, pgprot_t prot)
{
        pte_t pte;

        phys >>= PAGE_SHIFT;

        switch (idx) {
        case FIX_BTMAP_END ... FIX_BTMAP_BEGIN:
#ifdef CONFIG_X86_F00F_BUG
        case FIX_F00F_IDT:
#endif
#ifdef CONFIG_X86_32
        case FIX_WP_TEST:
        case FIX_VDSO:
# ifdef CONFIG_HIGHMEM
        case FIX_KMAP_BEGIN ... FIX_KMAP_END:
# endif
#else
        case VSYSCALL_LAST_PAGE ... VSYSCALL_FIRST_PAGE:
#endif
#ifdef CONFIG_X86_LOCAL_APIC
        case FIX_APIC_BASE:     /* maps dummy local APIC */
#endif
                pte = pfn_pte(phys, prot);
                break;

        default:
                pte = mfn_pte(phys, prot);
                break;
        }

        __native_set_fixmap(idx, pte);

#ifdef CONFIG_X86_64
        /* Replicate changes to map the vsyscall page into the user
           pagetable vsyscall mapping. */
        if (idx >= VSYSCALL_LAST_PAGE && idx <= VSYSCALL_FIRST_PAGE) {
                unsigned long vaddr = __fix_to_virt(idx);
                set_pte_vaddr_pud(level3_user_vsyscall, vaddr, pte);
        }
#endif
}

static const struct pv_info xen_info __initdata = {
        .paravirt_enabled = 1,
        .shared_kernel_pmd = 0,

        .name = "Xen",
};

static const struct pv_init_ops xen_init_ops __initdata = {
        .patch = xen_patch,

        .banner = xen_banner,
        .memory_setup = xen_memory_setup,
        .arch_setup = xen_arch_setup,
        .post_allocator_init = xen_post_allocator_init,
};

static const struct pv_time_ops xen_time_ops __initdata = {
        .time_init = xen_time_init,

        .set_wallclock = xen_set_wallclock,
        .get_wallclock = xen_get_wallclock,
        .get_tsc_khz = xen_tsc_khz,
        .sched_clock = xen_sched_clock,
};

static const struct pv_cpu_ops xen_cpu_ops __initdata = {
        .cpuid = xen_cpuid,

        .set_debugreg = xen_set_debugreg,
        .get_debugreg = xen_get_debugreg,

        .clts = xen_clts,

        .read_cr0 = native_read_cr0,
        .write_cr0 = xen_write_cr0,

        .read_cr4 = native_read_cr4,
        .read_cr4_safe = native_read_cr4_safe,
        .write_cr4 = xen_write_cr4,

        .wbinvd = native_wbinvd,

        .read_msr = native_read_msr_safe,
        .write_msr = xen_write_msr_safe,
        .read_tsc = native_read_tsc,
        .read_pmc = native_read_pmc,

        .iret = xen_iret,
        .irq_enable_sysexit = xen_sysexit,
#ifdef CONFIG_X86_64
        .usergs_sysret32 = xen_sysret32,
        .usergs_sysret64 = xen_sysret64,
#endif

        .load_tr_desc = paravirt_nop,
        .set_ldt = xen_set_ldt,
        .load_gdt = xen_load_gdt,
        .load_idt = xen_load_idt,
        .load_tls = xen_load_tls,
#ifdef CONFIG_X86_64
        .load_gs_index = xen_load_gs_index,
#endif

        .alloc_ldt = xen_alloc_ldt,
        .free_ldt = xen_free_ldt,

        .store_gdt = native_store_gdt,
        .store_idt = native_store_idt,
        .store_tr = xen_store_tr,

        .write_ldt_entry = xen_write_ldt_entry,
        .write_gdt_entry = xen_write_gdt_entry,
        .write_idt_entry = xen_write_idt_entry,
        .load_sp0 = xen_load_sp0,

        .set_iopl_mask = xen_set_iopl_mask,
        .io_delay = xen_io_delay,

        /* Xen takes care of %gs when switching to usermode for us */
        .swapgs = paravirt_nop,

        .lazy_mode = {
                .enter = paravirt_enter_lazy_cpu,
                .leave = xen_leave_lazy,
        },
};

static const struct pv_apic_ops xen_apic_ops __initdata = {
#ifdef CONFIG_X86_LOCAL_APIC
        .apic_write = xen_apic_write,
        .apic_read = xen_apic_read,
        .setup_boot_clock = paravirt_nop,
        .setup_secondary_clock = paravirt_nop,
        .startup_ipi_hook = paravirt_nop,
#endif
};

static const struct pv_mmu_ops xen_mmu_ops __initdata = {
        .pagetable_setup_start = xen_pagetable_setup_start,
        .pagetable_setup_done = xen_pagetable_setup_done,

        .read_cr2 = xen_read_cr2,
        .write_cr2 = xen_write_cr2,

        .read_cr3 = xen_read_cr3,
        .write_cr3 = xen_write_cr3,

        .flush_tlb_user = xen_flush_tlb,
        .flush_tlb_kernel = xen_flush_tlb,
        .flush_tlb_single = xen_flush_tlb_single,
        .flush_tlb_others = xen_flush_tlb_others,

        .pte_update = paravirt_nop,
        .pte_update_defer = paravirt_nop,

        .pgd_alloc = xen_pgd_alloc,
        .pgd_free = xen_pgd_free,

        .alloc_pte = xen_alloc_pte_init,
        .release_pte = xen_release_pte_init,
        .alloc_pmd = xen_alloc_pte_init,
        .alloc_pmd_clone = paravirt_nop,
        .release_pmd = xen_release_pte_init,

#ifdef CONFIG_HIGHPTE
        .kmap_atomic_pte = xen_kmap_atomic_pte,
#endif

#ifdef CONFIG_X86_64
        .set_pte = xen_set_pte,
#else
        .set_pte = xen_set_pte_init,
#endif
        .set_pte_at = xen_set_pte_at,
        .set_pmd = xen_set_pmd_hyper,

        .ptep_modify_prot_start = __ptep_modify_prot_start,
        .ptep_modify_prot_commit = __ptep_modify_prot_commit,

        .pte_val = xen_pte_val,
        .pte_flags = native_pte_flags,
        .pgd_val = xen_pgd_val,

        .make_pte = xen_make_pte,
        .make_pgd = xen_make_pgd,

#ifdef CONFIG_X86_PAE
        .set_pte_atomic = xen_set_pte_atomic,
        .set_pte_present = xen_set_pte_at,
        .pte_clear = xen_pte_clear,
        .pmd_clear = xen_pmd_clear,
#endif  /* CONFIG_X86_PAE */
        .set_pud = xen_set_pud_hyper,

        .make_pmd = xen_make_pmd,
        .pmd_val = xen_pmd_val,

#if PAGETABLE_LEVELS == 4
        .pud_val = xen_pud_val,
        .make_pud = xen_make_pud,
        .set_pgd = xen_set_pgd_hyper,

        .alloc_pud = xen_alloc_pte_init,
        .release_pud = xen_release_pte_init,
#endif  /* PAGETABLE_LEVELS == 4 */

        .activate_mm = xen_activate_mm,
        .dup_mmap = xen_dup_mmap,
        .exit_mmap = xen_exit_mmap,

        .lazy_mode = {
                .enter = paravirt_enter_lazy_mmu,
                .leave = xen_leave_lazy,
        },

        .set_fixmap = xen_set_fixmap,
};

static void xen_reboot(int reason)
{
        struct sched_shutdown r = { .reason = reason };

#ifdef CONFIG_SMP
        smp_send_stop();
#endif

        if (HYPERVISOR_sched_op(SCHEDOP_shutdown, &r))
                BUG();
}

static void xen_restart(char *msg)
{
        xen_reboot(SHUTDOWN_reboot);
}

static void xen_emergency_restart(void)
{
        xen_reboot(SHUTDOWN_reboot);
}

static void xen_machine_halt(void)
{
        xen_reboot(SHUTDOWN_poweroff);
}

static void xen_crash_shutdown(struct pt_regs *regs)
{
        xen_reboot(SHUTDOWN_crash);
}

static const struct machine_ops __initdata xen_machine_ops = {
        .restart = xen_restart,
        .halt = xen_machine_halt,
        .power_off = xen_machine_halt,
        .shutdown = xen_machine_halt,
        .crash_shutdown = xen_crash_shutdown,
        .emergency_restart = xen_emergency_restart,
};


static void __init xen_reserve_top(void)
{
#ifdef CONFIG_X86_32
        unsigned long top = HYPERVISOR_VIRT_START;
        struct xen_platform_parameters pp;

        if (HYPERVISOR_xen_version(XENVER_platform_parameters, &pp) == 0)
                top = pp.virt_start;

        reserve_top_address(-top + 2 * PAGE_SIZE);
#endif  /* CONFIG_X86_32 */
}

/*
 * Like __va(), but returns address in the kernel mapping (which is
 * all we have until the physical memory mapping has been set up.
 */
static void *__ka(phys_addr_t paddr)
{
#ifdef CONFIG_X86_64
        return (void *)(paddr + __START_KERNEL_map);
#else
        return __va(paddr);
#endif
}

/* Convert a machine address to physical address */
static unsigned long m2p(phys_addr_t maddr)
{
        phys_addr_t paddr;

        maddr &= PTE_PFN_MASK;
        paddr = mfn_to_pfn(maddr >> PAGE_SHIFT) << PAGE_SHIFT;

        return paddr;
}

/* Convert a machine address to kernel virtual */
static void *m2v(phys_addr_t maddr)
{
        return __ka(m2p(maddr));
}

#ifdef CONFIG_X86_64
static void walk(pgd_t *pgd, unsigned long addr)
{
        unsigned l4idx = pgd_index(addr);
        unsigned l3idx = pud_index(addr);
        unsigned l2idx = pmd_index(addr);
        unsigned l1idx = pte_index(addr);
        pgd_t l4;
        pud_t l3;
        pmd_t l2;
        pte_t l1;

        xen_raw_printk("walk %p, %lx -> %d %d %d %d\n",
                       pgd, addr, l4idx, l3idx, l2idx, l1idx);

        l4 = pgd[l4idx];
        xen_raw_printk("  l4: %016lx\n", l4.pgd);
        xen_raw_printk("      %016lx\n", pgd_val(l4));

        l3 = ((pud_t *)(m2v(l4.pgd)))[l3idx];
        xen_raw_printk("  l3: %016lx\n", l3.pud);
        xen_raw_printk("      %016lx\n", pud_val(l3));

        l2 = ((pmd_t *)(m2v(l3.pud)))[l2idx];
        xen_raw_printk("  l2: %016lx\n", l2.pmd);
        xen_raw_printk("      %016lx\n", pmd_val(l2));

        l1 = ((pte_t *)(m2v(l2.pmd)))[l1idx];
        xen_raw_printk("  l1: %016lx\n", l1.pte);
        xen_raw_printk("      %016lx\n", pte_val(l1));
}
#endif

static void set_page_prot(void *addr, pgprot_t prot)
{
        unsigned long pfn = __pa(addr) >> PAGE_SHIFT;
        pte_t pte = pfn_pte(pfn, prot);

        xen_raw_printk("addr=%p pfn=%lx mfn=%lx prot=%016llx pte=%016llx\n",
                       addr, pfn, get_phys_to_machine(pfn),
                       pgprot_val(prot), pte.pte);

        if (HYPERVISOR_update_va_mapping((unsigned long)addr, pte, 0))
                BUG();
}

static __init void xen_map_identity_early(pmd_t *pmd, unsigned long max_pfn)
{
        unsigned pmdidx, pteidx;
        unsigned ident_pte;
        unsigned long pfn;

        ident_pte = 0;
        pfn = 0;
        for(pmdidx = 0; pmdidx < PTRS_PER_PMD && pfn < max_pfn; pmdidx++) {
                pte_t *pte_page;

                /* Reuse or allocate a page of ptes */
                if (pmd_present(pmd[pmdidx]))
                        pte_page = m2v(pmd[pmdidx].pmd);
                else {
                        /* Check for free pte pages */
                        if (ident_pte == ARRAY_SIZE(level1_ident_pgt))
                                break;

                        pte_page = &level1_ident_pgt[ident_pte];
                        ident_pte += PTRS_PER_PTE;

                        pmd[pmdidx] = __pmd(__pa(pte_page) | _PAGE_TABLE);
                }

                /* Install mappings */
                for(pteidx = 0; pteidx < PTRS_PER_PTE; pteidx++, pfn++) {
                        pte_t pte;

                        if (pfn > max_pfn_mapped)
                                max_pfn_mapped = pfn;

                        if (!pte_none(pte_page[pteidx]))
                                continue;

                        pte = pfn_pte(pfn, PAGE_KERNEL_EXEC);
                        pte_page[pteidx] = pte;
                }
        }

        for(pteidx = 0; pteidx < ident_pte; pteidx += PTRS_PER_PTE)
                set_page_prot(&level1_ident_pgt[pteidx], PAGE_KERNEL_RO);

        set_page_prot(pmd, PAGE_KERNEL_RO);
}

#ifdef CONFIG_X86_64
static void convert_pfn_mfn(void *v)
{
        pte_t *pte = v;
        int i;

        /* All levels are converted the same way, so just treat them
           as ptes. */
        for(i = 0; i < PTRS_PER_PTE; i++)
                pte[i] = xen_make_pte(pte[i].pte);
}

/*
 * Set up the inital kernel pagetable.
 *
 * We can construct this by grafting the Xen provided pagetable into
 * head_64.S's preconstructed pagetables.  We copy the Xen L2's into
 * level2_ident_pgt, level2_kernel_pgt and level2_fixmap_pgt.  This
 * means that only the kernel has a physical mapping to start with -
 * but that's enough to get __va working.  We need to fill in the rest
 * of the physical mapping once some sort of allocator has been set
 * up.
 */
static __init pgd_t *xen_setup_kernel_pagetable(pgd_t *pgd, unsigned long max_pfn)
{
        pud_t *l3;
        pmd_t *l2;

        /* Zap identity mapping */
        init_level4_pgt[0] = __pgd(0);

        /* Pre-constructed entries are in pfn, so convert to mfn */
        convert_pfn_mfn(init_level4_pgt);
        convert_pfn_mfn(level3_ident_pgt);
        convert_pfn_mfn(level3_kernel_pgt);

        l3 = m2v(pgd[pgd_index(__START_KERNEL_map)].pgd);
        l2 = m2v(l3[pud_index(__START_KERNEL_map)].pud);

        memcpy(level2_ident_pgt, l2, sizeof(pmd_t) * PTRS_PER_PMD);
        memcpy(level2_kernel_pgt, l2, sizeof(pmd_t) * PTRS_PER_PMD);

        l3 = m2v(pgd[pgd_index(__START_KERNEL_map + PMD_SIZE)].pgd);
        l2 = m2v(l3[pud_index(__START_KERNEL_map + PMD_SIZE)].pud);
        memcpy(level2_fixmap_pgt, l2, sizeof(pmd_t) * PTRS_PER_PMD);

        /* Set up identity map */
        xen_map_identity_early(level2_ident_pgt, max_pfn);

        /* Make pagetable pieces RO */
        set_page_prot(init_level4_pgt, PAGE_KERNEL_RO);
        set_page_prot(level3_ident_pgt, PAGE_KERNEL_RO);
        set_page_prot(level3_kernel_pgt, PAGE_KERNEL_RO);
        set_page_prot(level3_user_vsyscall, PAGE_KERNEL_RO);
        set_page_prot(level2_kernel_pgt, PAGE_KERNEL_RO);
        set_page_prot(level2_fixmap_pgt, PAGE_KERNEL_RO);

        /* Pin down new L4 */
        pin_pagetable_pfn(MMUEXT_PIN_L4_TABLE,
                          PFN_DOWN(__pa_symbol(init_level4_pgt)));

        /* Unpin Xen-provided one */
        pin_pagetable_pfn(MMUEXT_UNPIN_TABLE, PFN_DOWN(__pa(pgd)));

        /* Switch over */
        pgd = init_level4_pgt;

        /*
         * At this stage there can be no user pgd, and no page
         * structure to attach it to, so make sure we just set kernel
         * pgd.
         */
        xen_mc_batch();
        __xen_write_cr3(true, __pa(pgd));
        xen_mc_issue(PARAVIRT_LAZY_CPU);

        reserve_early(__pa(xen_start_info->pt_base),
                      __pa(xen_start_info->pt_base +
                           xen_start_info->nr_pt_frames * PAGE_SIZE),
                      "XEN PAGETABLES");

        return pgd;
}
#else   /* !CONFIG_X86_64 */
static pmd_t level2_kernel_pgt[PTRS_PER_PMD] __page_aligned_bss;

static __init pgd_t *xen_setup_kernel_pagetable(pgd_t *pgd, unsigned long max_pfn)
{
        pmd_t *kernel_pmd;

        init_pg_tables_start = __pa(pgd);
        init_pg_tables_end = __pa(pgd) + xen_start_info->nr_pt_frames*PAGE_SIZE;
        max_pfn_mapped = PFN_DOWN(init_pg_tables_end + 512*1024);

        kernel_pmd = m2v(pgd[KERNEL_PGD_BOUNDARY].pgd);
        memcpy(level2_kernel_pgt, kernel_pmd, sizeof(pmd_t) * PTRS_PER_PMD);

        xen_map_identity_early(level2_kernel_pgt, max_pfn);

        memcpy(swapper_pg_dir, pgd, sizeof(pgd_t) * PTRS_PER_PGD);
        set_pgd(&swapper_pg_dir[KERNEL_PGD_BOUNDARY],
                        __pgd(__pa(level2_kernel_pgt) | _PAGE_PRESENT));

        set_page_prot(level2_kernel_pgt, PAGE_KERNEL_RO);
        set_page_prot(swapper_pg_dir, PAGE_KERNEL_RO);
        set_page_prot(empty_zero_page, PAGE_KERNEL_RO);

        pin_pagetable_pfn(MMUEXT_UNPIN_TABLE, PFN_DOWN(__pa(pgd)));

        xen_write_cr3(__pa(swapper_pg_dir));

        pin_pagetable_pfn(MMUEXT_PIN_L3_TABLE, PFN_DOWN(__pa(swapper_pg_dir)));

        return swapper_pg_dir;
}
#endif  /* CONFIG_X86_64 */

/* First C function to be called on Xen boot */
asmlinkage void __init xen_start_kernel(void)
{
        pgd_t *pgd;

        if (!xen_start_info)
                return;

        BUG_ON(memcmp(xen_start_info->magic, "xen-3", 5) != 0);

        xen_setup_features();

        /* Install Xen paravirt ops */
        pv_info = xen_info;
        pv_init_ops = xen_init_ops;
        pv_time_ops = xen_time_ops;
        pv_cpu_ops = xen_cpu_ops;
        pv_apic_ops = xen_apic_ops;
        pv_mmu_ops = xen_mmu_ops;

        xen_init_irq_ops();

        if (xen_feature(XENFEAT_mmu_pt_update_preserve_ad)) {
                pv_mmu_ops.ptep_modify_prot_start = xen_ptep_modify_prot_start;
                pv_mmu_ops.ptep_modify_prot_commit = xen_ptep_modify_prot_commit;
        }

        machine_ops = xen_machine_ops;

#ifdef CONFIG_X86_64
        /* Disable until direct per-cpu data access. */
        have_vcpu_info_placement = 0;
        x86_64_init_pda();
#endif

        xen_smp_init();

        /* Get mfn list */
        if (!xen_feature(XENFEAT_auto_translated_physmap))
                xen_build_dynamic_phys_to_machine();

        pgd = (pgd_t *)xen_start_info->pt_base;

        /* Prevent unwanted bits from being set in PTEs. */
        __supported_pte_mask &= ~_PAGE_GLOBAL;
        if (!is_initial_xendomain())
                __supported_pte_mask &= ~(_PAGE_PWT | _PAGE_PCD);

        /* Don't do the full vcpu_info placement stuff until we have a
           possible map and a non-dummy shared_info. */
        per_cpu(xen_vcpu, 0) = &HYPERVISOR_shared_info->vcpu_info[0];

        xen_raw_console_write("mapping kernel into physical memory\n");
        pgd = xen_setup_kernel_pagetable(pgd, xen_start_info->nr_pages);

        init_mm.pgd = pgd;

        /* keep using Xen gdt for now; no urgent need to change it */

        pv_info.kernel_rpl = 1;
        if (xen_feature(XENFEAT_supervisor_mode_kernel))
                pv_info.kernel_rpl = 0;

        /* set the limit of our address space */
        xen_reserve_top();

#ifdef CONFIG_X86_32
        /* set up basic CPUID stuff */
        cpu_detect(&new_cpu_data);
        new_cpu_data.hard_math = 1;
        new_cpu_data.x86_capability[0] = cpuid_edx(1);
#endif

        /* Poke various useful things into boot_params */
        boot_params.hdr.type_of_loader = (9 << 4) | 0;
        boot_params.hdr.ramdisk_image = xen_start_info->mod_start
                ? __pa(xen_start_info->mod_start) : 0;
        boot_params.hdr.ramdisk_size = xen_start_info->mod_len;
        boot_params.hdr.cmd_line_ptr = __pa(xen_start_info->cmd_line);

        if (!is_initial_xendomain()) {
                add_preferred_console("xenboot", 0, NULL);
                add_preferred_console("tty", 0, NULL);
                add_preferred_console("hvc", 0, NULL);
        }

        xen_raw_console_write("about to get started...\n");

#if 0
        xen_raw_printk("&boot_params=%p __pa(&boot_params)=%lx __va(__pa(&boot_params))=%lx\n",
                       &boot_params, __pa_symbol(&boot_params),
                       __va(__pa_symbol(&boot_params)));

        walk(pgd, &boot_params);
        walk(pgd, __va(__pa(&boot_params)));
#endif

        /* Start the world */
#ifdef CONFIG_X86_32
        i386_start_kernel();
#else
        x86_64_start_reservations((char *)__pa_symbol(&boot_params));
#endif
}