* (such as the example in Documentation/lguest/lguest.c) is called the
* Launcher.
*
- * Secondly, we only run specially modified Guests, not normal kernels. When
- * you set CONFIG_LGUEST to 'y' or 'm', this automatically sets
- * CONFIG_LGUEST_GUEST=y, which compiles this file into the kernel so it knows
- * how to be a Guest. This means that you can use the same kernel you boot
- * normally (ie. as a Host) as a Guest.
+ * Secondly, we only run specially modified Guests, not normal kernels: setting
+ * CONFIG_LGUEST_GUEST to "y" compiles this file into the kernel so it knows
+ * how to be a Guest at boot time. This means that you can use the same kernel
+ * you boot normally (ie. as a Host) as a Guest.
*
* These Guests know that they cannot do privileged operations, such as disable
* interrupts, and that they have to ask the Host to do such things explicitly.
* This file consists of all the replacements for such low-level native
* hardware operations: these special Guest versions call the Host.
*
- * So how does the kernel know it's a Guest? The Guest starts at a special
- * entry point marked with a magic string, which sets up a few things then
- * calls here. We replace the native functions various "paravirt" structures
- * with our Guest versions, then boot like normal. :*/
+ * So how does the kernel know it's a Guest? We'll see that later, but let's
+ * just say that we end up here where we replace the native functions various
+ * "paravirt" structures with our Guest versions, then boot like normal. :*/
/*
* Copyright (C) 2006, Rusty Russell <rusty@rustcorp.com.au> IBM Corporation.
* lguest_leave_lazy_mode().
*
* So, when we're in lazy mode, we call async_hcall() to store the call for
- * future processing. */
+ * future processing: */
static void lazy_hcall(unsigned long call,
unsigned long arg1,
unsigned long arg2,
}
/* When lazy mode is turned off reset the per-cpu lazy mode variable and then
- * issue a hypercall to flush any stored calls. */
+ * issue the do-nothing hypercall to flush any stored calls. */
static void lguest_leave_lazy_mode(void)
{
paravirt_leave_lazy(paravirt_get_lazy_mode());
*
* So instead we keep an "irq_enabled" field inside our "struct lguest_data",
* which the Guest can update with a single instruction. The Host knows to
- * check there when it wants to deliver an interrupt.
+ * check there before it tries to deliver an interrupt.
*/
/* save_flags() is expected to return the processor state (ie. "flags"). The
/*M:003 Note that we don't check for outstanding interrupts when we re-enable
* them (or when we unmask an interrupt). This seems to work for the moment,
* since interrupts are rare and we'll just get the interrupt on the next timer
- * tick, but when we turn on CONFIG_NO_HZ, we should revisit this. One way
+ * tick, but now we can run with CONFIG_NO_HZ, we should revisit this. One way
* would be to put the "irq_enabled" field in a page by itself, and have the
* Host write-protect it when an interrupt comes in when irqs are disabled.
- * There will then be a page fault as soon as interrupts are re-enabled. :*/
+ * There will then be a page fault as soon as interrupts are re-enabled.
+ *
+ * A better method is to implement soft interrupt disable generally for x86:
+ * instead of disabling interrupts, we set a flag. If an interrupt does come
+ * in, we then disable them for real. This is uncommon, so we could simply use
+ * a hypercall for interrupt control and not worry about efficiency. :*/
/*G:034
* The Interrupt Descriptor Table (IDT).
static void lguest_write_idt_entry(gate_desc *dt,
int entrynum, const gate_desc *g)
{
+ /* The gate_desc structure is 8 bytes long: we hand it to the Host in
+ * two 32-bit chunks. The whole 32-bit kernel used to hand descriptors
+ * around like this; typesafety wasn't a big concern in Linux's early
+ * years. */
u32 *desc = (u32 *)g;
/* Keep the local copy up to date. */
native_write_idt_entry(dt, entrynum, g);
*
* This is the opposite of the IDT code where we have a LOAD_IDT_ENTRY
* hypercall and use that repeatedly to load a new IDT. I don't think it
- * really matters, but wouldn't it be nice if they were the same?
+ * really matters, but wouldn't it be nice if they were the same? Wouldn't
+ * it be even better if you were the one to send the patch to fix it?
*/
static void lguest_load_gdt(const struct desc_ptr *desc)
{
/* The "cpuid" instruction is a way of querying both the CPU identity
* (manufacturer, model, etc) and its features. It was introduced before the
- * Pentium in 1993 and keeps getting extended by both Intel and AMD. As you
- * might imagine, after a decade and a half this treatment, it is now a giant
- * ball of hair. Its entry in the current Intel manual runs to 28 pages.
+ * Pentium in 1993 and keeps getting extended by both Intel, AMD and others.
+ * As you might imagine, after a decade and a half this treatment, it is now a
+ * giant ball of hair. Its entry in the current Intel manual runs to 28 pages.
*
* This instruction even it has its own Wikipedia entry. The Wikipedia entry
* has been translated into 4 languages. I am not making this up!
int vector = FIRST_EXTERNAL_VECTOR + i;
if (vector != SYSCALL_VECTOR) {
set_intr_gate(vector, interrupt[i]);
- set_irq_chip_and_handler(i, &lguest_irq_controller,
- handle_level_irq);
+ set_irq_chip_and_handler_name(i, &lguest_irq_controller,
+ handle_level_irq,
+ "level");
}
}
/* This call is required to set up for 4k stacks, where we have
return lguest_data.time.tv_sec;
}
-/* The TSC is a Time Stamp Counter. The Host tells us what speed it runs at,
- * or 0 if it's unusable as a reliable clock source. This matches what we want
- * here: if we return 0 from this function, the x86 TSC clock will not register
- * itself. */
+/* The TSC is an Intel thing called the Time Stamp Counter. The Host tells us
+ * what speed it runs at, or 0 if it's unusable as a reliable clock source.
+ * This matches what we want here: if we return 0 from this function, the x86
+ * TSC clock will give up and not register itself. */
static unsigned long lguest_cpu_khz(void)
{
return lguest_data.tsc_khz;
}
-/* If we can't use the TSC, the kernel falls back to our "lguest_clock", where
- * we read the time value given to us by the Host. */
+/* If we can't use the TSC, the kernel falls back to our lower-priority
+ * "lguest_clock", where we read the time value given to us by the Host. */
static cycle_t lguest_clock_read(void)
{
unsigned long sec, nsec;
static int lguest_clockevent_set_next_event(unsigned long delta,
struct clock_event_device *evt)
{
+ /* FIXME: I don't think this can ever happen, but James tells me he had
+ * to put this code in. Maybe we should remove it now. Anyone? */
if (delta < LG_CLOCK_MIN_DELTA) {
if (printk_ratelimit())
printk(KERN_DEBUG "%s: small delta %lu ns\n",
- __FUNCTION__, delta);
+ __func__, delta);
return -ETIME;
}
+
+ /* Please wake us this far in the future. */
hcall(LHCALL_SET_CLOCKEVENT, delta, 0, 0);
return 0;
}
* will not tolerate us trying to use that), the stack pointer, and the number
* of pages in the stack. */
static void lguest_load_sp0(struct tss_struct *tss,
- struct thread_struct *thread)
+ struct thread_struct *thread)
{
lazy_hcall(LHCALL_SET_STACK, __KERNEL_DS|0x1, thread->sp0,
THREAD_SIZE/PAGE_SIZE);
hcall(LHCALL_HALT, 0, 0, 0);
}
-/* Perhaps CRASH isn't the best name for this hypercall, but we use it to get a
- * message out when we're crashing as well as elegant termination like powering
- * off.
+/* The SHUTDOWN hypercall takes a string to describe what's happening, and
+ * an argument which says whether this to restart (reboot) the Guest or not.
*
* Note that the Host always prefers that the Guest speak in physical addresses
* rather than virtual addresses, so we use __pa() here. */
/* Setting up memory is fairly easy. */
static __init char *lguest_memory_setup(void)
{
- /* We do this here and not earlier because lockcheck barfs if we do it
- * before start_kernel() */
+ /* We do this here and not earlier because lockcheck used to barf if we
+ * did it before start_kernel(). I think we fixed that, so it'd be
+ * nice to move it back to lguest_init. Patch welcome... */
atomic_notifier_chain_register(&panic_notifier_list, &paniced);
/* The Linux bootloader header contains an "e820" memory map: the
return len;
}
+/* Rebooting also tells the Host we're finished, but the RESTART flag tells the
+ * Launcher to reboot us. */
+static void lguest_restart(char *reason)
+{
+ hcall(LHCALL_SHUTDOWN, __pa(reason), LGUEST_SHUTDOWN_RESTART, 0);
+}
+
/*G:050
* Patching (Powerfully Placating Performance Pedants)
*
- * We have already seen that pv_ops structures let us replace simple
- * native instructions with calls to the appropriate back end all throughout
- * the kernel. This allows the same kernel to run as a Guest and as a native
+ * We have already seen that pv_ops structures let us replace simple native
+ * instructions with calls to the appropriate back end all throughout the
+ * kernel. This allows the same kernel to run as a Guest and as a native
* kernel, but it's slow because of all the indirect branches.
*
* Remember that David Wheeler quote about "Any problem in computer science can
return insn_len;
}
-static void lguest_restart(char *reason)
-{
- hcall(LHCALL_SHUTDOWN, __pa(reason), LGUEST_SHUTDOWN_RESTART, 0);
-}
-
-/*G:030 Once we get to lguest_init(), we know we're a Guest. The pv_ops
- * structures in the kernel provide points for (almost) every routine we have
- * to override to avoid privileged instructions. */
+/*G:030 Once we get to lguest_init(), we know we're a Guest. The various
+ * pv_ops structures in the kernel provide points for (almost) every routine we
+ * have to override to avoid privileged instructions. */
__init void lguest_init(void)
{
/* We're under lguest, paravirt is enabled, and we're running at
* clobbered. The Launcher places our initial pagetables somewhere at
* the top of our physical memory, so we don't need extra space: set
* init_pg_tables_end to the end of the kernel. */
+ init_pg_tables_start = __pa(pg0);
init_pg_tables_end = __pa(pg0);
/* Load the %fs segment register (the per-cpu segment register) with
* the normal data segment to get through booting. */
asm volatile ("mov %0, %%fs" : : "r" (__KERNEL_DS) : "memory");
- /* The Host uses the top of the Guest's virtual address space for the
- * Host<->Guest Switcher, and it tells us how big that is in
- * lguest_data.reserve_mem, set up on the LGUEST_INIT hypercall. */
+ /* The Host<->Guest Switcher lives at the top of our address space, and
+ * the Host told us how big it is when we made LGUEST_INIT hypercall:
+ * it put the answer in lguest_data.reserve_mem */
reserve_top_address(lguest_data.reserve_mem);
/* If we don't initialize the lock dependency checker now, it crashes
/* Math is always hard! */
new_cpu_data.hard_math = 1;
+ /* We don't have features. We have puppies! Puppies! */
#ifdef CONFIG_X86_MCE
mce_disabled = 1;
#endif
virtio_cons_early_init(early_put_chars);
/* Last of all, we set the power management poweroff hook to point to
- * the Guest routine to power off. */
+ * the Guest routine to power off, and the reboot hook to our restart
+ * routine. */
pm_power_off = lguest_power_off;
-
machine_ops.restart = lguest_restart;
- /* Now we're set up, call start_kernel() in init/main.c and we proceed
+
+ /* Now we're set up, call i386_start_kernel() in head32.c and we proceed
* to boot as normal. It never returns. */
- start_kernel();
+ i386_start_kernel();
}
/*
* This marks the end of stage II of our journey, The Guest.
git://ftp.safe.ca / safe / jmp / linux-2.6 / blobdiff