xen: implement ptep_modify_prot_start/commit

[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/interface/sched.h>
#include <xen/features.h>
#include <xen/page.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/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);

/*
 * 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 * out of date, but it will never be set early).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)
{
        printk(KERN_INFO "Booting paravirtualized kernel on %s\n",
               pv_info.name);
        printk(KERN_INFO "Hypervisor signature: %s%s\n",
               xen_start_info->magic,
               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 unsigned long xen_save_fl(void)
{
        struct vcpu_info *vcpu;
        unsigned long flags;

        vcpu = x86_read_percpu(xen_vcpu);

        /* flag has opposite sense of mask */
        flags = !vcpu->evtchn_upcall_mask;

        /* convert to IF type flag
           -0 -> 0x00000000
           -1 -> 0xffffffff
        */
        return (-flags) & X86_EFLAGS_IF;
}

static void xen_restore_fl(unsigned long flags)
{
        struct vcpu_info *vcpu;

        /* convert from IF type flag */
        flags = !(flags & X86_EFLAGS_IF);

        /* There's a one instruction preempt window here.  We need to
           make sure we're don't switch CPUs between getting the vcpu
           pointer and updating the mask. */
        preempt_disable();
        vcpu = x86_read_percpu(xen_vcpu);
        vcpu->evtchn_upcall_mask = flags;
        preempt_enable_no_resched();

        /* Doesn't matter if we get preempted here, because any
           pending event will get dealt with anyway. */

        if (flags == 0) {
                preempt_check_resched();
                barrier(); /* unmask then check (avoid races) */
                if (unlikely(vcpu->evtchn_upcall_pending))
                        force_evtchn_callback();
        }
}

static void xen_irq_disable(void)
{
        /* There's a one instruction preempt window here.  We need to
           make sure we're don't switch CPUs between getting the vcpu
           pointer and updating the mask. */
        preempt_disable();
        x86_read_percpu(xen_vcpu)->evtchn_upcall_mask = 1;
        preempt_enable_no_resched();
}

static void xen_irq_enable(void)
{
        struct vcpu_info *vcpu;

        /* We don't need to worry about being preempted here, since
           either a) interrupts are disabled, so no preemption, or b)
           the caller is confused and is trying to re-enable interrupts
           on an indeterminate processor. */

        vcpu = x86_read_percpu(xen_vcpu);
        vcpu->evtchn_upcall_mask = 0;

        /* Doesn't matter if we get preempted here, because any
           pending event will get dealt with anyway. */

        barrier(); /* unmask then check (avoid races) */
        if (unlikely(vcpu->evtchn_upcall_pending))
                force_evtchn_callback();
}

static void xen_safe_halt(void)
{
        /* Blocking includes an implicit local_irq_enable(). */
        if (HYPERVISOR_sched_op(SCHEDOP_block, NULL) != 0)
                BUG();
}

static void xen_halt(void)
{
        if (irqs_disabled())
                HYPERVISOR_vcpu_op(VCPUOP_down, smp_processor_id(), NULL);
        else
                xen_safe_halt();
}

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;
}

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)
{
        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);

        /*
         * 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.
         */
        if (paravirt_get_lazy_mode() == PARAVIRT_LAZY_CPU)
                loadsegment(gs, 0);
}

static void xen_write_ldt_entry(struct desc_struct *dt, int entrynum,
                                const void *ptr)
{
        unsigned long lp = (unsigned long)&dt[entrynum];
        xmaddr_t mach_lp = virt_to_machine(lp);
        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, u32 low, u32 high,
                            struct trap_info *info)
{
        u8 type, dpl;

        type = (high >> 8) & 0x1f;
        dpl = (high >> 13) & 3;

        if (type != 0xf && type != 0xe)
                return 0;

        info->vector = vector;
        info->address = (high & 0xffff0000) | (low & 0x0000ffff);
        info->cs = low >> 16;
        info->flags = dpl;
        /* interrupt gates clear IF */
        if (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];
                u32 *desc = (u32 *)g;

                info[1].address = 0;

                if (cvt_gate_to_trap(entrynum, desc[0], desc[1], &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) / 8;
        BUG_ON(count > 256);

        for (in = out = 0; in < count; in++) {
                const u32 *entry = (u32 *)(desc->address + in * 8);

                if (cvt_gate_to_trap(in, entry[0], entry[1], &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(unsigned long cr3)
{
        struct mmuext_op *op;
        struct multicall_space mcs;
        unsigned long mfn = pfn_to_mfn(PFN_DOWN(cr3));

        BUG_ON(preemptible());

        mcs = xen_mc_entry(sizeof(*op));  /* disables interrupts */

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

        op = mcs.args;
        op->cmd = MMUEXT_NEW_BASEPTR;
        op->arg1.mfn = mfn;

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

        /* Update xen_update_cr3 once the batch has actually
           been submitted. */
        xen_mc_callback(set_current_cr3, (void *)cr3);

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

/* 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(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);
}

/* 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);
}

#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)
{
        pgd_t *xen_pgd = (pgd_t *)xen_start_info->pt_base;
        int i;

        /* special set_pte for pagetable initialization */
        pv_mmu_ops.set_pte = xen_set_pte_init;

        init_mm.pgd = base;
        /*
         * copy top-level of Xen-supplied pagetable into place.  This
         * is a stand-in while we copy the pmd pages.
         */
        memcpy(base, xen_pgd, PTRS_PER_PGD * sizeof(pgd_t));

        /*
         * For PAE, need to allocate new pmds, rather than
         * share Xen's, since Xen doesn't like pmd's being
         * shared between address spaces.
         */
        for (i = 0; i < PTRS_PER_PGD; i++) {
                if (pgd_val_ma(xen_pgd[i]) & _PAGE_PRESENT) {
                        pmd_t *pmd = (pmd_t *)alloc_bootmem_low_pages(PAGE_SIZE);

                        memcpy(pmd, (void *)pgd_page_vaddr(xen_pgd[i]),
                               PAGE_SIZE);

                        make_lowmem_page_readonly(pmd);

                        set_pgd(&base[i], __pgd(1 + __pa(pmd)));
                } else
                        pgd_clear(&base[i]);
        }

        /* make sure zero_page is mapped RO so we can use it in pagetables */
        make_lowmem_page_readonly(empty_zero_page);
        make_lowmem_page_readonly(base);
        /*
         * Switch to new pagetable.  This is done before
         * pagetable_init has done anything so that the new pages
         * added to the table can be prepared properly for Xen.
         */
        xen_write_cr3(__pa(base));

        /* Unpin initial Xen pagetable */
        pin_pagetable_pfn(MMUEXT_UNPIN_TABLE,
                          PFN_DOWN(__pa(xen_start_info->pt_base)));
}

void xen_setup_shared_info(void)
{
        if (!xen_feature(XENFEAT_auto_translated_physmap)) {
                unsigned long addr = fix_to_virt(FIX_PARAVIRT_BOOTMAP);

                /*
                 * Create a mapping for the shared info page.
                 * Should be set_fixmap(), but shared_info is a machine
                 * address with no corresponding pseudo-phys address.
                 */
                set_pte_mfn(addr,
                            PFN_DOWN(xen_start_info->shared_info),
                            PAGE_KERNEL);

                HYPERVISOR_shared_info = (struct shared_info *)addr;
        } 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)
{
        /* 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;
        pv_mmu_ops.set_pte = xen_set_pte;

        xen_setup_shared_info();

        /* Actually pin the pagetable down, but we can't set PG_pinned
           yet because the page structures don't exist yet. */
        pin_pagetable_pfn(MMUEXT_PIN_L3_TABLE, PFN_DOWN(__pa(base)));
}

static __init void xen_post_allocator_init(void)
{
        pv_mmu_ops.set_pmd = xen_set_pmd;
        pv_mmu_ops.set_pud = xen_set_pud;

        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 */
        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;
        }
}

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) {
                SITE(pv_irq_ops, irq_enable);
                SITE(pv_irq_ops, irq_disable);
                SITE(pv_irq_ops, save_fl);
                SITE(pv_irq_ops, restore_fl);
#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 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_cpu_khz = xen_cpu_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 = native_write_msr_safe,
        .read_tsc = native_read_tsc,
        .read_pmc = native_read_pmc,

        .iret = xen_iret,
        .irq_enable_syscall_ret = xen_sysexit,

        .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,

        .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,

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

static const struct pv_irq_ops xen_irq_ops __initdata = {
        .init_IRQ = xen_init_IRQ,
        .save_fl = xen_save_fl,
        .restore_fl = xen_restore_fl,
        .irq_disable = xen_irq_disable,
        .irq_enable = xen_irq_enable,
        .safe_halt = xen_safe_halt,
        .halt = xen_halt,
};

static const struct pv_apic_ops xen_apic_ops __initdata = {
#ifdef CONFIG_X86_LOCAL_APIC
        .apic_write = xen_apic_write,
        .apic_write_atomic = 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,

        .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

        .set_pte = NULL,        /* see xen_pagetable_setup_* */
        .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_val,
        .pgd_val = xen_pgd_val,

        .make_pte = xen_make_pte,
        .make_pgd = xen_make_pgd,

        .set_pte_atomic = xen_set_pte_atomic,
        .set_pte_present = xen_set_pte_at,
        .set_pud = xen_set_pud_hyper,
        .pte_clear = xen_pte_clear,
        .pmd_clear = xen_pmd_clear,

        .make_pmd = xen_make_pmd,
        .pmd_val = xen_pmd_val,

        .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,
        },
};

#ifdef CONFIG_SMP
static const struct smp_ops xen_smp_ops __initdata = {
        .smp_prepare_boot_cpu = xen_smp_prepare_boot_cpu,
        .smp_prepare_cpus = xen_smp_prepare_cpus,
        .cpu_up = xen_cpu_up,
        .smp_cpus_done = xen_smp_cpus_done,

        .smp_send_stop = xen_smp_send_stop,
        .smp_send_reschedule = xen_smp_send_reschedule,
        .smp_call_function_mask = xen_smp_call_function_mask,
};
#endif  /* CONFIG_SMP */

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)
{
        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);
}

/* 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_irq_ops = xen_irq_ops;
        pv_apic_ops = xen_apic_ops;
        pv_mmu_ops = xen_mmu_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_SMP
        smp_ops = xen_smp_ops;
#endif

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

        pgd = (pgd_t *)xen_start_info->pt_base;

        init_pg_tables_end = __pa(pgd) + xen_start_info->nr_pt_frames*PAGE_SIZE;

        init_mm.pgd = pgd; /* use the Xen pagetables to start */

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

        x86_write_percpu(xen_cr3, __pa(pgd));
        x86_write_percpu(xen_current_cr3, __pa(pgd));

        /* 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];

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

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

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

        /* 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);

        /* 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;

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

        /* Start the world */
        start_kernel();
}