Linux-2.6.33.2/arch/x86/lguest/boot.c
/*P:010
* A hypervisor allows multiple Operating Systems to run on a single machine.
* To quote David Wheeler: "Any problem in computer science can be solved with
* another layer of indirection."
*
* We keep things simple in two ways. First, we start with a normal Linux
* kernel and insert a module (lg.ko) which allows us to run other Linux
* kernels the same way we'd run processes. We call the first kernel the Host,
* and the others the Guests. The program which sets up and configures Guests
* (such as the example in Documentation/lguest/lguest.c) is called the
* Launcher.
*
* 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? 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.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
* NON INFRINGEMENT. See the GNU General Public License for more
* details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/
#include <linux/kernel.h>
#include <linux/start_kernel.h>
#include <linux/string.h>
#include <linux/console.h>
#include <linux/screen_info.h>
#include <linux/irq.h>
#include <linux/interrupt.h>
#include <linux/clocksource.h>
#include <linux/clockchips.h>
#include <linux/lguest.h>
#include <linux/lguest_launcher.h>
#include <linux/virtio_console.h>
#include <linux/pm.h>
#include <asm/apic.h>
#include <asm/lguest.h>
#include <asm/paravirt.h>
#include <asm/param.h>
#include <asm/page.h>
#include <asm/pgtable.h>
#include <asm/desc.h>
#include <asm/setup.h>
#include <asm/e820.h>
#include <asm/mce.h>
#include <asm/io.h>
#include <asm/i387.h>
#include <asm/stackprotector.h>
#include <asm/reboot.h> /* for struct machine_ops */
/*G:010 Welcome to the Guest!
*
* The Guest in our tale is a simple creature: identical to the Host but
* behaving in simplified but equivalent ways. In particular, the Guest is the
* same kernel as the Host (or at least, built from the same source code).
:*/
struct lguest_data lguest_data = {
.hcall_status = { [0 ... LHCALL_RING_SIZE-1] = 0xFF },
.noirq_start = (u32)lguest_noirq_start,
.noirq_end = (u32)lguest_noirq_end,
.kernel_address = PAGE_OFFSET,
.blocked_interrupts = { 1 }, /* Block timer interrupts */
.syscall_vec = SYSCALL_VECTOR,
};
/*G:037
* async_hcall() is pretty simple: I'm quite proud of it really. We have a
* ring buffer of stored hypercalls which the Host will run though next time we
* do a normal hypercall. Each entry in the ring has 5 slots for the hypercall
* arguments, and a "hcall_status" word which is 0 if the call is ready to go,
* and 255 once the Host has finished with it.
*
* If we come around to a slot which hasn't been finished, then the table is
* full and we just make the hypercall directly. This has the nice side
* effect of causing the Host to run all the stored calls in the ring buffer
* which empties it for next time!
*/
static void async_hcall(unsigned long call, unsigned long arg1,
unsigned long arg2, unsigned long arg3,
unsigned long arg4)
{
/* Note: This code assumes we're uniprocessor. */
static unsigned int next_call;
unsigned long flags;
/*
* Disable interrupts if not already disabled: we don't want an
* interrupt handler making a hypercall while we're already doing
* one!
*/
local_irq_save(flags);
if (lguest_data.hcall_status[next_call] != 0xFF) {
/* Table full, so do normal hcall which will flush table. */
kvm_hypercall4(call, arg1, arg2, arg3, arg4);
} else {
lguest_data.hcalls[next_call].arg0 = call;
lguest_data.hcalls[next_call].arg1 = arg1;
lguest_data.hcalls[next_call].arg2 = arg2;
lguest_data.hcalls[next_call].arg3 = arg3;
lguest_data.hcalls[next_call].arg4 = arg4;
/* Arguments must all be written before we mark it to go */
wmb();
lguest_data.hcall_status[next_call] = 0;
if (++next_call == LHCALL_RING_SIZE)
next_call = 0;
}
local_irq_restore(flags);
}
/*G:035
* Notice the lazy_hcall() above, rather than hcall(). This is our first real
* optimization trick!
*
* When lazy_mode is set, it means we're allowed to defer all hypercalls and do
* them as a batch when lazy_mode is eventually turned off. Because hypercalls
* are reasonably expensive, batching them up makes sense. For example, a
* large munmap might update dozens of page table entries: that code calls
* paravirt_enter_lazy_mmu(), does the dozen updates, then calls
* lguest_leave_lazy_mode().
*
* So, when we're in lazy mode, we call async_hcall() to store the call for
* future processing:
*/
static void lazy_hcall1(unsigned long call,
unsigned long arg1)
{
if (paravirt_get_lazy_mode() == PARAVIRT_LAZY_NONE)
kvm_hypercall1(call, arg1);
else
async_hcall(call, arg1, 0, 0, 0);
}
/* You can imagine what lazy_hcall2, 3 and 4 look like. :*/
static void lazy_hcall2(unsigned long call,
unsigned long arg1,
unsigned long arg2)
{
if (paravirt_get_lazy_mode() == PARAVIRT_LAZY_NONE)
kvm_hypercall2(call, arg1, arg2);
else
async_hcall(call, arg1, arg2, 0, 0);
}
static void lazy_hcall3(unsigned long call,
unsigned long arg1,
unsigned long arg2,
unsigned long arg3)
{
if (paravirt_get_lazy_mode() == PARAVIRT_LAZY_NONE)
kvm_hypercall3(call, arg1, arg2, arg3);
else
async_hcall(call, arg1, arg2, arg3, 0);
}
#ifdef CONFIG_X86_PAE
static void lazy_hcall4(unsigned long call,
unsigned long arg1,
unsigned long arg2,
unsigned long arg3,
unsigned long arg4)
{
if (paravirt_get_lazy_mode() == PARAVIRT_LAZY_NONE)
kvm_hypercall4(call, arg1, arg2, arg3, arg4);
else
async_hcall(call, arg1, arg2, arg3, arg4);
}
#endif
/*G:036
* When lazy mode is turned off reset the per-cpu lazy mode variable and then
* issue the do-nothing hypercall to flush any stored calls.
:*/
static void lguest_leave_lazy_mmu_mode(void)
{
kvm_hypercall0(LHCALL_FLUSH_ASYNC);
paravirt_leave_lazy_mmu();
}
static void lguest_end_context_switch(struct task_struct *next)
{
kvm_hypercall0(LHCALL_FLUSH_ASYNC);
paravirt_end_context_switch(next);
}
/*G:032
* After that diversion we return to our first native-instruction
* replacements: four functions for interrupt control.
*
* The simplest way of implementing these would be to have "turn interrupts
* off" and "turn interrupts on" hypercalls. Unfortunately, this is too slow:
* these are by far the most commonly called functions of those we override.
*
* 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 before it tries to deliver an interrupt.
*/
/*
* save_flags() is expected to return the processor state (ie. "flags"). The
* flags word contains all kind of stuff, but in practice Linux only cares
* about the interrupt flag. Our "save_flags()" just returns that.
*/
static unsigned long save_fl(void)
{
return lguest_data.irq_enabled;
}
/* Interrupts go off... */
static void irq_disable(void)
{
lguest_data.irq_enabled = 0;
}
/*
* Let's pause a moment. Remember how I said these are called so often?
* Jeremy Fitzhardinge optimized them so hard early in 2009 that he had to
* break some rules. In particular, these functions are assumed to save their
* own registers if they need to: normal C functions assume they can trash the
* eax register. To use normal C functions, we use
* PV_CALLEE_SAVE_REGS_THUNK(), which pushes %eax onto the stack, calls the
* C function, then restores it.
*/
PV_CALLEE_SAVE_REGS_THUNK(save_fl);
PV_CALLEE_SAVE_REGS_THUNK(irq_disable);
/*:*/
/* These are in i386_head.S */
extern void lg_irq_enable(void);
extern void lg_restore_fl(unsigned long flags);
/*M:003
* We could be more efficient in our checking of outstanding interrupts, rather
* than using a branch. 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.
*
* 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).
*
* The IDT tells the processor what to do when an interrupt comes in. Each
* entry in the table is a 64-bit descriptor: this holds the privilege level,
* address of the handler, and... well, who cares? The Guest just asks the
* Host to make the change anyway, because the Host controls the real 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);
/* Tell Host about this new entry. */
kvm_hypercall3(LHCALL_LOAD_IDT_ENTRY, entrynum, desc[0], desc[1]);
}
/*
* Changing to a different IDT is very rare: we keep the IDT up-to-date every
* time it is written, so we can simply loop through all entries and tell the
* Host about them.
*/
static void lguest_load_idt(const struct desc_ptr *desc)
{
unsigned int i;
struct desc_struct *idt = (void *)desc->address;
for (i = 0; i < (desc->size+1)/8; i++)
kvm_hypercall3(LHCALL_LOAD_IDT_ENTRY, i, idt[i].a, idt[i].b);
}
/*
* The Global Descriptor Table.
*
* The Intel architecture defines another table, called the Global Descriptor
* Table (GDT). You tell the CPU where it is (and its size) using the "lgdt"
* instruction, and then several other instructions refer to entries in the
* table. There are three entries which the Switcher needs, so the Host simply
* controls the entire thing and the Guest asks it to make changes using the
* LOAD_GDT hypercall.
*
* This is the exactly like the IDT code.
*/
static void lguest_load_gdt(const struct desc_ptr *desc)
{
unsigned int i;
struct desc_struct *gdt = (void *)desc->address;
for (i = 0; i < (desc->size+1)/8; i++)
kvm_hypercall3(LHCALL_LOAD_GDT_ENTRY, i, gdt[i].a, gdt[i].b);
}
/*
* For a single GDT entry which changes, we do the lazy thing: alter our GDT,
* then tell the Host to reload the entire thing. This operation is so rare
* that this naive implementation is reasonable.
*/
static void lguest_write_gdt_entry(struct desc_struct *dt, int entrynum,
const void *desc, int type)
{
native_write_gdt_entry(dt, entrynum, desc, type);
/* Tell Host about this new entry. */
kvm_hypercall3(LHCALL_LOAD_GDT_ENTRY, entrynum,
dt[entrynum].a, dt[entrynum].b);
}
/*
* OK, I lied. There are three "thread local storage" GDT entries which change
* on every context switch (these three entries are how glibc implements
* __thread variables). So we have a hypercall specifically for this case.
*/
static void lguest_load_tls(struct thread_struct *t, unsigned int cpu)
{
/*
* There's one problem which normal hardware doesn't have: the Host
* can't handle us removing entries we're currently using. So we clear
* the GS register here: if it's needed it'll be reloaded anyway.
*/
lazy_load_gs(0);
lazy_hcall2(LHCALL_LOAD_TLS, __pa(&t->tls_array), cpu);
}
/*G:038
* That's enough excitement for now, back to ploughing through each of the
* different pv_ops structures (we're about 1/3 of the way through).
*
* This is the Local Descriptor Table, another weird Intel thingy. Linux only
* uses this for some strange applications like Wine. We don't do anything
* here, so they'll get an informative and friendly Segmentation Fault.
*/
static void lguest_set_ldt(const void *addr, unsigned entries)
{
}
/*
* This loads a GDT entry into the "Task Register": that entry points to a
* structure called the Task State Segment. Some comments scattered though the
* kernel code indicate that this used for task switching in ages past, along
* with blood sacrifice and astrology.
*
* Now there's nothing interesting in here that we don't get told elsewhere.
* But the native version uses the "ltr" instruction, which makes the Host
* complain to the Guest about a Segmentation Fault and it'll oops. So we
* override the native version with a do-nothing version.
*/
static void lguest_load_tr_desc(void)
{
}
/*
* 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, 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 5 languages. I am not making this up!
*
* We could get funky here and identify ourselves as "GenuineLguest", but
* instead we just use the real "cpuid" instruction. Then I pretty much turned
* off feature bits until the Guest booted. (Don't say that: you'll damage
* lguest sales!) Shut up, inner voice! (Hey, just pointing out that this is
* hardly future proof.) Noone's listening! They don't like you anyway,
* parenthetic weirdo!
*
* Replacing the cpuid so we can turn features off is great for the kernel, but
* anyone (including userspace) can just use the raw "cpuid" instruction and
* the Host won't even notice since it isn't privileged. So we try not to get
* too worked up about it.
*/
static void lguest_cpuid(unsigned int *ax, unsigned int *bx,
unsigned int *cx, unsigned int *dx)
{
int function = *ax;
native_cpuid(ax, bx, cx, dx);
switch (function) {
/*
* CPUID 0 gives the highest legal CPUID number (and the ID string).
* We futureproof our code a little by sticking to known CPUID values.
*/
case 0:
if (*ax > 5)
*ax = 5;
break;
/*
* CPUID 1 is a basic feature request.
*
* CX: we only allow kernel to see SSE3, CMPXCHG16B and SSSE3
* DX: SSE, SSE2, FXSR, MMX, CMOV, CMPXCHG8B, TSC, FPU and PAE.
*/
case 1:
*cx &= 0x00002201;
*dx &= 0x07808151;
/*
* The Host can do a nice optimization if it knows that the
* kernel mappings (addresses above 0xC0000000 or whatever
* PAGE_OFFSET is set to) haven't changed. But Linux calls
* flush_tlb_user() for both user and kernel mappings unless
* the Page Global Enable (PGE) feature bit is set.
*/
*dx |= 0x00002000;
/*
* We also lie, and say we're family id 5. 6 or greater
* leads to a rdmsr in early_init_intel which we can't handle.
* Family ID is returned as bits 8-12 in ax.
*/
*ax &= 0xFFFFF0FF;
*ax |= 0x00000500;
break;
/*
* 0x80000000 returns the highest Extended Function, so we futureproof
* like we do above by limiting it to known fields.
*/
case 0x80000000:
if (*ax > 0x80000008)
*ax = 0x80000008;
break;
/*
* PAE systems can mark pages as non-executable. Linux calls this the
* NX bit. Intel calls it XD (eXecute Disable), AMD EVP (Enhanced
* Virus Protection). We just switch turn if off here, since we don't
* support it.
*/
case 0x80000001:
*dx &= ~(1 << 20);
break;
}
}
/*
* Intel has four control registers, imaginatively named cr0, cr2, cr3 and cr4.
* I assume there's a cr1, but it hasn't bothered us yet, so we'll not bother
* it. The Host needs to know when the Guest wants to change them, so we have
* a whole series of functions like read_cr0() and write_cr0().
*
* We start with cr0. cr0 allows you to turn on and off all kinds of basic
* features, but Linux only really cares about one: the horrifically-named Task
* Switched (TS) bit at bit 3 (ie. 8)
*
* What does the TS bit do? Well, it causes the CPU to trap (interrupt 7) if
* the floating point unit is used. Which allows us to restore FPU state
* lazily after a task switch, and Linux uses that gratefully, but wouldn't a
* name like "FPUTRAP bit" be a little less cryptic?
*
* We store cr0 locally because the Host never changes it. The Guest sometimes
* wants to read it and we'd prefer not to bother the Host unnecessarily.
*/
static unsigned long current_cr0;
static void lguest_write_cr0(unsigned long val)
{
lazy_hcall1(LHCALL_TS, val & X86_CR0_TS);
current_cr0 = val;
}
static unsigned long lguest_read_cr0(void)
{
return current_cr0;
}
/*
* Intel provided a special instruction to clear the TS bit for people too cool
* to use write_cr0() to do it. This "clts" instruction is faster, because all
* the vowels have been optimized out.
*/
static void lguest_clts(void)
{
lazy_hcall1(LHCALL_TS, 0);
current_cr0 &= ~X86_CR0_TS;
}
/*
* cr2 is the virtual address of the last page fault, which the Guest only ever
* reads. The Host kindly writes this into our "struct lguest_data", so we
* just read it out of there.
*/
static unsigned long lguest_read_cr2(void)
{
return lguest_data.cr2;
}
/* See lguest_set_pte() below. */
static bool cr3_changed = false;
/*
* cr3 is the current toplevel pagetable page: the principle is the same as
* cr0. Keep a local copy, and tell the Host when it changes. The only
* difference is that our local copy is in lguest_data because the Host needs
* to set it upon our initial hypercall.
*/
static void lguest_write_cr3(unsigned long cr3)
{
lguest_data.pgdir = cr3;
lazy_hcall1(LHCALL_NEW_PGTABLE, cr3);
cr3_changed = true;
}
static unsigned long lguest_read_cr3(void)
{
return lguest_data.pgdir;
}
/* cr4 is used to enable and disable PGE, but we don't care. */
static unsigned long lguest_read_cr4(void)
{
return 0;
}
static void lguest_write_cr4(unsigned long val)
{
}
/*
* Page Table Handling.
*
* Now would be a good time to take a rest and grab a coffee or similarly
* relaxing stimulant. The easy parts are behind us, and the trek gradually
* winds uphill from here.
*
* Quick refresher: memory is divided into "pages" of 4096 bytes each. The CPU
* maps virtual addresses to physical addresses using "page tables". We could
* use one huge index of 1 million entries: each address is 4 bytes, so that's
* 1024 pages just to hold the page tables. But since most virtual addresses
* are unused, we use a two level index which saves space. The cr3 register
* contains the physical address of the top level "page directory" page, which
* contains physical addresses of up to 1024 second-level pages. Each of these
* second level pages contains up to 1024 physical addresses of actual pages,
* or Page Table Entries (PTEs).
*
* Here's a diagram, where arrows indicate physical addresses:
*
* cr3 ---> +---------+
* | --------->+---------+
* | | | PADDR1 |
* Mid-level | | PADDR2 |
* (PMD) page | | |
* | | Lower-level |
* | | (PTE) page |
* | | | |
* .... ....
*
* So to convert a virtual address to a physical address, we look up the top
* level, which points us to the second level, which gives us the physical
* address of that page. If the top level entry was not present, or the second
* level entry was not present, then the virtual address is invalid (we
* say "the page was not mapped").
*
* Put another way, a 32-bit virtual address is divided up like so:
*
* 1 1 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
* |<---- 10 bits ---->|<---- 10 bits ---->|<------ 12 bits ------>|
* Index into top Index into second Offset within page
* page directory page pagetable page
*
* Now, unfortunately, this isn't the whole story: Intel added Physical Address
* Extension (PAE) to allow 32 bit systems to use 64GB of memory (ie. 36 bits).
* These are held in 64-bit page table entries, so we can now only fit 512
* entries in a page, and the neat three-level tree breaks down.
*
* The result is a four level page table:
*
* cr3 --> [ 4 Upper ]
* [ Level ]
* [ Entries ]
* [(PUD Page)]---> +---------+
* | --------->+---------+
* | | | PADDR1 |
* Mid-level | | PADDR2 |
* (PMD) page | | |
* | | Lower-level |
* | | (PTE) page |
* | | | |
* .... ....
*
*
* And the virtual address is decoded as:
*
* 1 1 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
* |<-2->|<--- 9 bits ---->|<---- 9 bits --->|<------ 12 bits ------>|
* Index into Index into mid Index into lower Offset within page
* top entries directory page pagetable page
*
* It's too hard to switch between these two formats at runtime, so Linux only
* supports one or the other depending on whether CONFIG_X86_PAE is set. Many
* distributions turn it on, and not just for people with silly amounts of
* memory: the larger PTE entries allow room for the NX bit, which lets the
* kernel disable execution of pages and increase security.
*
* This was a problem for lguest, which couldn't run on these distributions;
* then Matias Zabaljauregui figured it all out and implemented it, and only a
* handful of puppies were crushed in the process!
*
* Back to our point: the kernel spends a lot of time changing both the
* top-level page directory and lower-level pagetable pages. The Guest doesn't
* know physical addresses, so while it maintains these page tables exactly
* like normal, it also needs to keep the Host informed whenever it makes a
* change: the Host will create the real page tables based on the Guests'.
*/
/*
* The Guest calls this after it has set a second-level entry (pte), ie. to map
* a page into a process' address space. Wetell the Host the toplevel and
* address this corresponds to. The Guest uses one pagetable per process, so
* we need to tell the Host which one we're changing (mm->pgd).
*/
static void lguest_pte_update(struct mm_struct *mm, unsigned long addr,
pte_t *ptep)
{
#ifdef CONFIG_X86_PAE
/* PAE needs to hand a 64 bit page table entry, so it uses two args. */
lazy_hcall4(LHCALL_SET_PTE, __pa(mm->pgd), addr,
ptep->pte_low, ptep->pte_high);
#else
lazy_hcall3(LHCALL_SET_PTE, __pa(mm->pgd), addr, ptep->pte_low);
#endif
}
/* This is the "set and update" combo-meal-deal version. */
static void lguest_set_pte_at(struct mm_struct *mm, unsigned long addr,
pte_t *ptep, pte_t pteval)
{
native_set_pte(ptep, pteval);
lguest_pte_update(mm, addr, ptep);
}
/*
* The Guest calls lguest_set_pud to set a top-level entry and lguest_set_pmd
* to set a middle-level entry when PAE is activated.
*
* Again, we set the entry then tell the Host which page we changed,
* and the index of the entry we changed.
*/
#ifdef CONFIG_X86_PAE
static void lguest_set_pud(pud_t *pudp, pud_t pudval)
{
native_set_pud(pudp, pudval);
/* 32 bytes aligned pdpt address and the index. */
lazy_hcall2(LHCALL_SET_PGD, __pa(pudp) & 0xFFFFFFE0,
(__pa(pudp) & 0x1F) / sizeof(pud_t));
}
static void lguest_set_pmd(pmd_t *pmdp, pmd_t pmdval)
{
native_set_pmd(pmdp, pmdval);
lazy_hcall2(LHCALL_SET_PMD, __pa(pmdp) & PAGE_MASK,
(__pa(pmdp) & (PAGE_SIZE - 1)) / sizeof(pmd_t));
}
#else
/* The Guest calls lguest_set_pmd to set a top-level entry when !PAE. */
static void lguest_set_pmd(pmd_t *pmdp, pmd_t pmdval)
{
native_set_pmd(pmdp, pmdval);
lazy_hcall2(LHCALL_SET_PGD, __pa(pmdp) & PAGE_MASK,
(__pa(pmdp) & (PAGE_SIZE - 1)) / sizeof(pmd_t));
}
#endif
/*
* There are a couple of legacy places where the kernel sets a PTE, but we
* don't know the top level any more. This is useless for us, since we don't
* know which pagetable is changing or what address, so we just tell the Host
* to forget all of them. Fortunately, this is very rare.
*
* ... except in early boot when the kernel sets up the initial pagetables,
* which makes booting astonishingly slow: 1.83 seconds! So we don't even tell
* the Host anything changed until we've done the first page table switch,
* which brings boot back to 0.25 seconds.
*/
static void lguest_set_pte(pte_t *ptep, pte_t pteval)
{
native_set_pte(ptep, pteval);
if (cr3_changed)
lazy_hcall1(LHCALL_FLUSH_TLB, 1);
}
#ifdef CONFIG_X86_PAE
/*
* With 64-bit PTE values, we need to be careful setting them: if we set 32
* bits at a time, the hardware could see a weird half-set entry. These
* versions ensure we update all 64 bits at once.
*/
static void lguest_set_pte_atomic(pte_t *ptep, pte_t pte)
{
native_set_pte_atomic(ptep, pte);
if (cr3_changed)
lazy_hcall1(LHCALL_FLUSH_TLB, 1);
}
static void lguest_pte_clear(struct mm_struct *mm, unsigned long addr,
pte_t *ptep)
{
native_pte_clear(mm, addr, ptep);
lguest_pte_update(mm, addr, ptep);
}
static void lguest_pmd_clear(pmd_t *pmdp)
{
lguest_set_pmd(pmdp, __pmd(0));
}
#endif
/*
* Unfortunately for Lguest, the pv_mmu_ops for page tables were based on
* native page table operations. On native hardware you can set a new page
* table entry whenever you want, but if you want to remove one you have to do
* a TLB flush (a TLB is a little cache of page table entries kept by the CPU).
*
* So the lguest_set_pte_at() and lguest_set_pmd() functions above are only
* called when a valid entry is written, not when it's removed (ie. marked not
* present). Instead, this is where we come when the Guest wants to remove a
* page table entry: we tell the Host to set that entry to 0 (ie. the present
* bit is zero).
*/
static void lguest_flush_tlb_single(unsigned long addr)
{
/* Simply set it to zero: if it was not, it will fault back in. */
lazy_hcall3(LHCALL_SET_PTE, lguest_data.pgdir, addr, 0);
}
/*
* This is what happens after the Guest has removed a large number of entries.
* This tells the Host that any of the page table entries for userspace might
* have changed, ie. virtual addresses below PAGE_OFFSET.
*/
static void lguest_flush_tlb_user(void)
{
lazy_hcall1(LHCALL_FLUSH_TLB, 0);
}
/*
* This is called when the kernel page tables have changed. That's not very
* common (unless the Guest is using highmem, which makes the Guest extremely
* slow), so it's worth separating this from the user flushing above.
*/
static void lguest_flush_tlb_kernel(void)
{
lazy_hcall1(LHCALL_FLUSH_TLB, 1);
}
/*
* The Unadvanced Programmable Interrupt Controller.
*
* This is an attempt to implement the simplest possible interrupt controller.
* I spent some time looking though routines like set_irq_chip_and_handler,
* set_irq_chip_and_handler_name, set_irq_chip_data and set_phasers_to_stun and
* I *think* this is as simple as it gets.
*
* We can tell the Host what interrupts we want blocked ready for using the
* lguest_data.interrupts bitmap, so disabling (aka "masking") them is as
* simple as setting a bit. We don't actually "ack" interrupts as such, we
* just mask and unmask them. I wonder if we should be cleverer?
*/
static void disable_lguest_irq(unsigned int irq)
{
set_bit(irq, lguest_data.blocked_interrupts);
}
static void enable_lguest_irq(unsigned int irq)
{
clear_bit(irq, lguest_data.blocked_interrupts);
}
/* This structure describes the lguest IRQ controller. */
static struct irq_chip lguest_irq_controller = {
.name = "lguest",
.mask = disable_lguest_irq,
.mask_ack = disable_lguest_irq,
.unmask = enable_lguest_irq,
};
/*
* This sets up the Interrupt Descriptor Table (IDT) entry for each hardware
* interrupt (except 128, which is used for system calls), and then tells the
* Linux infrastructure that each interrupt is controlled by our level-based
* lguest interrupt controller.
*/
static void __init lguest_init_IRQ(void)
{
unsigned int i;
for (i = FIRST_EXTERNAL_VECTOR; i < NR_VECTORS; i++) {
/* Some systems map "vectors" to interrupts weirdly. Not us! */
__get_cpu_var(vector_irq)[i] = i - FIRST_EXTERNAL_VECTOR;
if (i != SYSCALL_VECTOR)
set_intr_gate(i, interrupt[i - FIRST_EXTERNAL_VECTOR]);
}
/*
* This call is required to set up for 4k stacks, where we have
* separate stacks for hard and soft interrupts.
*/
irq_ctx_init(smp_processor_id());
}
/*
* With CONFIG_SPARSE_IRQ, interrupt descriptors are allocated as-needed, so
* rather than set them in lguest_init_IRQ we are called here every time an
* lguest device needs an interrupt.
*
* FIXME: irq_to_desc_alloc_node() can fail due to lack of memory, we should
* pass that up!
*/
void lguest_setup_irq(unsigned int irq)
{
irq_to_desc_alloc_node(irq, 0);
set_irq_chip_and_handler_name(irq, &lguest_irq_controller,
handle_level_irq, "level");
}
/*
* Time.
*
* It would be far better for everyone if the Guest had its own clock, but
* until then the Host gives us the time on every interrupt.
*/
static unsigned long lguest_get_wallclock(void)
{
return lguest_data.time.tv_sec;
}
/*
* 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_tsc_khz(void)
{
return lguest_data.tsc_khz;
}
/*
* 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(struct clocksource *cs)
{
unsigned long sec, nsec;
/*
* Since the time is in two parts (seconds and nanoseconds), we risk
* reading it just as it's changing from 99 & 0.999999999 to 100 and 0,
* and getting 99 and 0. As Linux tends to come apart under the stress
* of time travel, we must be careful:
*/
do {
/* First we read the seconds part. */
sec = lguest_data.time.tv_sec;
/*
* This read memory barrier tells the compiler and the CPU that
* this can't be reordered: we have to complete the above
* before going on.
*/
rmb();
/* Now we read the nanoseconds part. */
nsec = lguest_data.time.tv_nsec;
/* Make sure we've done that. */
rmb();
/* Now if the seconds part has changed, try again. */
} while (unlikely(lguest_data.time.tv_sec != sec));
/* Our lguest clock is in real nanoseconds. */
return sec*1000000000ULL + nsec;
}
/* This is the fallback clocksource: lower priority than the TSC clocksource. */
static struct clocksource lguest_clock = {
.name = "lguest",
.rating = 200,
.read = lguest_clock_read,
.mask = CLOCKSOURCE_MASK(64),
.mult = 1 << 22,
.shift = 22,
.flags = CLOCK_SOURCE_IS_CONTINUOUS,
};
/*
* We also need a "struct clock_event_device": Linux asks us to set it to go
* off some time in the future. Actually, James Morris figured all this out, I
* just applied the patch.
*/
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",
__func__, delta);
return -ETIME;
}
/* Please wake us this far in the future. */
kvm_hypercall1(LHCALL_SET_CLOCKEVENT, delta);
return 0;
}
static void lguest_clockevent_set_mode(enum clock_event_mode mode,
struct clock_event_device *evt)
{
switch (mode) {
case CLOCK_EVT_MODE_UNUSED:
case CLOCK_EVT_MODE_SHUTDOWN:
/* A 0 argument shuts the clock down. */
kvm_hypercall0(LHCALL_SET_CLOCKEVENT);
break;
case CLOCK_EVT_MODE_ONESHOT:
/* This is what we expect. */
break;
case CLOCK_EVT_MODE_PERIODIC:
BUG();
case CLOCK_EVT_MODE_RESUME:
break;
}
}
/* This describes our primitive timer chip. */
static struct clock_event_device lguest_clockevent = {
.name = "lguest",
.features = CLOCK_EVT_FEAT_ONESHOT,
.set_next_event = lguest_clockevent_set_next_event,
.set_mode = lguest_clockevent_set_mode,
.rating = INT_MAX,
.mult = 1,
.shift = 0,
.min_delta_ns = LG_CLOCK_MIN_DELTA,
.max_delta_ns = LG_CLOCK_MAX_DELTA,
};
/*
* This is the Guest timer interrupt handler (hardware interrupt 0). We just
* call the clockevent infrastructure and it does whatever needs doing.
*/
static void lguest_time_irq(unsigned int irq, struct irq_desc *desc)
{
unsigned long flags;
/* Don't interrupt us while this is running. */
local_irq_save(flags);
lguest_clockevent.event_handler(&lguest_clockevent);
local_irq_restore(flags);
}
/*
* At some point in the boot process, we get asked to set up our timing
* infrastructure. The kernel doesn't expect timer interrupts before this, but
* we cleverly initialized the "blocked_interrupts" field of "struct
* lguest_data" so that timer interrupts were blocked until now.
*/
static void lguest_time_init(void)
{
/* Set up the timer interrupt (0) to go to our simple timer routine */
set_irq_handler(0, lguest_time_irq);
clocksource_register(&lguest_clock);
/* We can't set cpumask in the initializer: damn C limitations! Set it
* here and register our timer device. */
lguest_clockevent.cpumask = cpumask_of(0);
clockevents_register_device(&lguest_clockevent);
/* Finally, we unblock the timer interrupt. */
enable_lguest_irq(0);
}
/*
* Miscellaneous bits and pieces.
*
* Here is an oddball collection of functions which the Guest needs for things
* to work. They're pretty simple.
*/
/*
* The Guest needs to tell the Host what stack it expects traps to use. For
* native hardware, this is part of the Task State Segment mentioned above in
* lguest_load_tr_desc(), but to help hypervisors there's this special call.
*
* We tell the Host the segment we want to use (__KERNEL_DS is the kernel data
* segment), the privilege level (we're privilege level 1, the Host is 0 and
* 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)
{
lazy_hcall3(LHCALL_SET_STACK, __KERNEL_DS | 0x1, thread->sp0,
THREAD_SIZE / PAGE_SIZE);
}
/* Let's just say, I wouldn't do debugging under a Guest. */
static void lguest_set_debugreg(int regno, unsigned long value)
{
/* FIXME: Implement */
}
/*
* There are times when the kernel wants to make sure that no memory writes are
* caught in the cache (that they've all reached real hardware devices). This
* doesn't matter for the Guest which has virtual hardware.
*
* On the Pentium 4 and above, cpuid() indicates that the Cache Line Flush
* (clflush) instruction is available and the kernel uses that. Otherwise, it
* uses the older "Write Back and Invalidate Cache" (wbinvd) instruction.
* Unlike clflush, wbinvd can only be run at privilege level 0. So we can
* ignore clflush, but replace wbinvd.
*/
static void lguest_wbinvd(void)
{
}
/*
* If the Guest expects to have an Advanced Programmable Interrupt Controller,
* we play dumb by ignoring writes and returning 0 for reads. So it's no
* longer Programmable nor Controlling anything, and I don't think 8 lines of
* code qualifies for Advanced. It will also never interrupt anything. It
* does, however, allow us to get through the Linux boot code.
*/
#ifdef CONFIG_X86_LOCAL_APIC
static void lguest_apic_write(u32 reg, u32 v)
{
}
static u32 lguest_apic_read(u32 reg)
{
return 0;
}
static u64 lguest_apic_icr_read(void)
{
return 0;
}
static void lguest_apic_icr_write(u32 low, u32 id)
{
/* Warn to see if there's any stray references */
WARN_ON(1);
}
static void lguest_apic_wait_icr_idle(void)
{
return;
}
static u32 lguest_apic_safe_wait_icr_idle(void)
{
return 0;
}
static void set_lguest_basic_apic_ops(void)
{
apic->read = lguest_apic_read;
apic->write = lguest_apic_write;
apic->icr_read = lguest_apic_icr_read;
apic->icr_write = lguest_apic_icr_write;
apic->wait_icr_idle = lguest_apic_wait_icr_idle;
apic->safe_wait_icr_idle = lguest_apic_safe_wait_icr_idle;
};
#endif
/* STOP! Until an interrupt comes in. */
static void lguest_safe_halt(void)
{
kvm_hypercall0(LHCALL_HALT);
}
/*
* 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.
*/
static void lguest_power_off(void)
{
kvm_hypercall2(LHCALL_SHUTDOWN, __pa("Power down"),
LGUEST_SHUTDOWN_POWEROFF);
}
/*
* Panicing.
*
* Don't. But if you did, this is what happens.
*/
static int lguest_panic(struct notifier_block *nb, unsigned long l, void *p)
{
kvm_hypercall2(LHCALL_SHUTDOWN, __pa(p), LGUEST_SHUTDOWN_POWEROFF);
/* The hcall won't return, but to keep gcc happy, we're "done". */
return NOTIFY_DONE;
}
static struct notifier_block paniced = {
.notifier_call = lguest_panic
};
/* Setting up memory is fairly easy. */
static __init char *lguest_memory_setup(void)
{
/*
*The Linux bootloader header contains an "e820" memory map: the
* Launcher populated the first entry with our memory limit.
*/
e820_add_region(boot_params.e820_map[0].addr,
boot_params.e820_map[0].size,
boot_params.e820_map[0].type);
/* This string is for the boot messages. */
return "LGUEST";
}
/*
* We will eventually use the virtio console device to produce console output,
* but before that is set up we use LHCALL_NOTIFY on normal memory to produce
* console output.
*/
static __init int early_put_chars(u32 vtermno, const char *buf, int count)
{
char scratch[17];
unsigned int len = count;
/* We use a nul-terminated string, so we make a copy. Icky, huh? */
if (len > sizeof(scratch) - 1)
len = sizeof(scratch) - 1;
scratch[len] = '\0';
memcpy(scratch, buf, len);
kvm_hypercall1(LHCALL_NOTIFY, __pa(scratch));
/* This routine returns the number of bytes actually written. */
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)
{
kvm_hypercall2(LHCALL_SHUTDOWN, __pa(reason), LGUEST_SHUTDOWN_RESTART);
}
/*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
* kernel, but it's slow because of all the indirect branches.
*
* Remember that David Wheeler quote about "Any problem in computer science can
* be solved with another layer of indirection"? The rest of that quote is
* "... But that usually will create another problem." This is the first of
* those problems.
*
* Our current solution is to allow the paravirt back end to optionally patch
* over the indirect calls to replace them with something more efficient. We
* patch two of the simplest of the most commonly called functions: disable
* interrupts and save interrupts. We usually have 6 or 10 bytes to patch
* into: the Guest versions of these operations are small enough that we can
* fit comfortably.
*
* First we need assembly templates of each of the patchable Guest operations,
* and these are in i386_head.S.
*/
/*G:060 We construct a table from the assembler templates: */
static const struct lguest_insns
{
const char *start, *end;
} lguest_insns[] = {
[PARAVIRT_PATCH(pv_irq_ops.irq_disable)] = { lgstart_cli, lgend_cli },
[PARAVIRT_PATCH(pv_irq_ops.save_fl)] = { lgstart_pushf, lgend_pushf },
};
/*
* Now our patch routine is fairly simple (based on the native one in
* paravirt.c). If we have a replacement, we copy it in and return how much of
* the available space we used.
*/
static unsigned lguest_patch(u8 type, u16 clobber, void *ibuf,
unsigned long addr, unsigned len)
{
unsigned int insn_len;
/* Don't do anything special if we don't have a replacement */
if (type >= ARRAY_SIZE(lguest_insns) || !lguest_insns[type].start)
return paravirt_patch_default(type, clobber, ibuf, addr, len);
insn_len = lguest_insns[type].end - lguest_insns[type].start;
/* Similarly if it can't fit (doesn't happen, but let's be thorough). */
if (len < insn_len)
return paravirt_patch_default(type, clobber, ibuf, addr, len);
/* Copy in our instructions. */
memcpy(ibuf, lguest_insns[type].start, insn_len);
return insn_len;
}
/*G:029
* 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. */
pv_info.name = "lguest";
/* Paravirt is enabled. */
pv_info.paravirt_enabled = 1;
/* We're running at privilege level 1, not 0 as normal. */
pv_info.kernel_rpl = 1;
/* Everyone except Xen runs with this set. */
pv_info.shared_kernel_pmd = 1;
/*
* We set up all the lguest overrides for sensitive operations. These
* are detailed with the operations themselves.
*/
/* Interrupt-related operations */
pv_irq_ops.save_fl = PV_CALLEE_SAVE(save_fl);
pv_irq_ops.restore_fl = __PV_IS_CALLEE_SAVE(lg_restore_fl);
pv_irq_ops.irq_disable = PV_CALLEE_SAVE(irq_disable);
pv_irq_ops.irq_enable = __PV_IS_CALLEE_SAVE(lg_irq_enable);
pv_irq_ops.safe_halt = lguest_safe_halt;
/* Setup operations */
pv_init_ops.patch = lguest_patch;
/* Intercepts of various CPU instructions */
pv_cpu_ops.load_gdt = lguest_load_gdt;
pv_cpu_ops.cpuid = lguest_cpuid;
pv_cpu_ops.load_idt = lguest_load_idt;
pv_cpu_ops.iret = lguest_iret;
pv_cpu_ops.load_sp0 = lguest_load_sp0;
pv_cpu_ops.load_tr_desc = lguest_load_tr_desc;
pv_cpu_ops.set_ldt = lguest_set_ldt;
pv_cpu_ops.load_tls = lguest_load_tls;
pv_cpu_ops.set_debugreg = lguest_set_debugreg;
pv_cpu_ops.clts = lguest_clts;
pv_cpu_ops.read_cr0 = lguest_read_cr0;
pv_cpu_ops.write_cr0 = lguest_write_cr0;
pv_cpu_ops.read_cr4 = lguest_read_cr4;
pv_cpu_ops.write_cr4 = lguest_write_cr4;
pv_cpu_ops.write_gdt_entry = lguest_write_gdt_entry;
pv_cpu_ops.write_idt_entry = lguest_write_idt_entry;
pv_cpu_ops.wbinvd = lguest_wbinvd;
pv_cpu_ops.start_context_switch = paravirt_start_context_switch;
pv_cpu_ops.end_context_switch = lguest_end_context_switch;
/* Pagetable management */
pv_mmu_ops.write_cr3 = lguest_write_cr3;
pv_mmu_ops.flush_tlb_user = lguest_flush_tlb_user;
pv_mmu_ops.flush_tlb_single = lguest_flush_tlb_single;
pv_mmu_ops.flush_tlb_kernel = lguest_flush_tlb_kernel;
pv_mmu_ops.set_pte = lguest_set_pte;
pv_mmu_ops.set_pte_at = lguest_set_pte_at;
pv_mmu_ops.set_pmd = lguest_set_pmd;
#ifdef CONFIG_X86_PAE
pv_mmu_ops.set_pte_atomic = lguest_set_pte_atomic;
pv_mmu_ops.pte_clear = lguest_pte_clear;
pv_mmu_ops.pmd_clear = lguest_pmd_clear;
pv_mmu_ops.set_pud = lguest_set_pud;
#endif
pv_mmu_ops.read_cr2 = lguest_read_cr2;
pv_mmu_ops.read_cr3 = lguest_read_cr3;
pv_mmu_ops.lazy_mode.enter = paravirt_enter_lazy_mmu;
pv_mmu_ops.lazy_mode.leave = lguest_leave_lazy_mmu_mode;
pv_mmu_ops.pte_update = lguest_pte_update;
pv_mmu_ops.pte_update_defer = lguest_pte_update;
#ifdef CONFIG_X86_LOCAL_APIC
/* APIC read/write intercepts */
set_lguest_basic_apic_ops();
#endif
x86_init.resources.memory_setup = lguest_memory_setup;
x86_init.irqs.intr_init = lguest_init_IRQ;
x86_init.timers.timer_init = lguest_time_init;
x86_platform.calibrate_tsc = lguest_tsc_khz;
x86_platform.get_wallclock = lguest_get_wallclock;
/*
* Now is a good time to look at the implementations of these functions
* before returning to the rest of lguest_init().
*/
/*G:070
* Now we've seen all the paravirt_ops, we return to
* lguest_init() where the rest of the fairly chaotic boot setup
* occurs.
*/
/*
* The stack protector is a weird thing where gcc places a canary
* value on the stack and then checks it on return. This file is
* compiled with -fno-stack-protector it, so we got this far without
* problems. The value of the canary is kept at offset 20 from the
* %gs register, so we need to set that up before calling C functions
* in other files.
*/
setup_stack_canary_segment(0);
/*
* We could just call load_stack_canary_segment(), but we might as well
* call switch_to_new_gdt() which loads the whole table and sets up the
* per-cpu segment descriptor register %fs as well.
*/
switch_to_new_gdt(0);
/* We actually boot with all memory mapped, but let's say 128MB. */
max_pfn_mapped = (128*1024*1024) >> PAGE_SHIFT;
/*
* 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
* atomic_notifier_chain_register, then paravirt_disable_iospace.
*/
lockdep_init();
/* Hook in our special panic hypercall code. */
atomic_notifier_chain_register(&panic_notifier_list, &paniced);
/*
* The IDE code spends about 3 seconds probing for disks: if we reserve
* all the I/O ports up front it can't get them and so doesn't probe.
* Other device drivers are similar (but less severe). This cuts the
* kernel boot time on my machine from 4.1 seconds to 0.45 seconds.
*/
paravirt_disable_iospace();
/*
* This is messy CPU setup stuff which the native boot code does before
* start_kernel, so we have to do, too:
*/
cpu_detect(&new_cpu_data);
/* head.S usually sets up the first capability word, so do it here. */
new_cpu_data.x86_capability[0] = cpuid_edx(1);
/* 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
#ifdef CONFIG_ACPI
acpi_disabled = 1;
acpi_ht = 0;
#endif
/*
* We set the preferred console to "hvc". This is the "hypervisor
* virtual console" driver written by the PowerPC people, which we also
* adapted for lguest's use.
*/
add_preferred_console("hvc", 0, NULL);
/* Register our very early console. */
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, 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 i386_start_kernel() in head32.c and we proceed
* to boot as normal. It never returns.
*/
i386_start_kernel();
}
/*
* This marks the end of stage II of our journey, The Guest.
*
* It is now time for us to explore the layer of virtual drivers and complete
* our understanding of the Guest in "make Drivers".
*/