/*P:400 This contains run_guest() which actually calls into the Host<->Guest
* Switcher and analyzes the return, such as determining if the Guest wants the
* Host to do something. This file also contains useful helper routines, and a
* couple of non-obvious setup and teardown pieces which were implemented after
* days of debugging pain. :*/
#include <linux/module.h>
#include <linux/stringify.h>
#include <linux/stddef.h>
#include <linux/io.h>
#include <linux/mm.h>
#include <linux/vmalloc.h>
#include <linux/cpu.h>
#include <linux/freezer.h>
#include <asm/paravirt.h>
#include <asm/desc.h>
#include <asm/pgtable.h>
#include <asm/uaccess.h>
#include <asm/poll.h>
#include <asm/highmem.h>
#include <asm/asm-offsets.h>
#include <asm/i387.h>
#include "lg.h"
/* Found in switcher.S */
extern char start_switcher_text[], end_switcher_text[], switch_to_guest[];
extern unsigned long default_idt_entries[];
/* Every guest maps the core switcher code. */
#define SHARED_SWITCHER_PAGES \
DIV_ROUND_UP(end_switcher_text - start_switcher_text, PAGE_SIZE)
/* Pages for switcher itself, then two pages per cpu */
#define TOTAL_SWITCHER_PAGES (SHARED_SWITCHER_PAGES + 2 * NR_CPUS)
/* We map at -4M for ease of mapping into the guest (one PTE page). */
#define SWITCHER_ADDR 0xFFC00000
static struct vm_struct *switcher_vma;
static struct page **switcher_page;
static int cpu_had_pge;
static struct {
unsigned long offset;
unsigned short segment;
} lguest_entry;
/* This One Big lock protects all inter-guest data structures. */
DEFINE_MUTEX(lguest_lock);
static DEFINE_PER_CPU(struct lguest *, last_guest);
/* FIXME: Make dynamic. */
#define MAX_LGUEST_GUESTS 16
struct lguest lguests[MAX_LGUEST_GUESTS];
/* Offset from where switcher.S was compiled to where we've copied it */
static unsigned long switcher_offset(void)
{
return SWITCHER_ADDR - (unsigned long)start_switcher_text;
}
/* This cpu's struct lguest_pages. */
static struct lguest_pages *lguest_pages(unsigned int cpu)
{
return &(((struct lguest_pages *)
(SWITCHER_ADDR + SHARED_SWITCHER_PAGES*PAGE_SIZE))[cpu]);
}
/*H:010 We need to set up the Switcher at a high virtual address. Remember the
* Switcher is a few hundred bytes of assembler code which actually changes the
* CPU to run the Guest, and then changes back to the Host when a trap or
* interrupt happens.
*
* The Switcher code must be at the same virtual address in the Guest as the
* Host since it will be running as the switchover occurs.
*
* Trying to map memory at a particular address is an unusual thing to do, so
* it's not a simple one-liner. We also set up the per-cpu parts of the
* Switcher here.
*/
static __init int map_switcher(void)
{
int i, err;
struct page **pagep;
/*
* Map the Switcher in to high memory.
*
* It turns out that if we choose the address 0xFFC00000 (4MB under the
* top virtual address), it makes setting up the page tables really
* easy.
*/
/* We allocate an array of "struct page"s. map_vm_area() wants the
* pages in this form, rather than just an array of pointers. */
switcher_page = kmalloc(sizeof(switcher_page[0])*TOTAL_SWITCHER_PAGES,
GFP_KERNEL);
if (!switcher_page) {
err = -ENOMEM;
goto out;
}
/* Now we actually allocate the pages. The Guest will see these pages,
* so we make sure they're zeroed. */
for (i = 0; i < TOTAL_SWITCHER_PAGES; i++) {
unsigned long addr = get_zeroed_page(GFP_KERNEL);
if (!addr) {
err = -ENOMEM;
goto free_some_pages;
}
switcher_page[i] = virt_to_page(addr);
}
/* Now we reserve the "virtual memory area" we want: 0xFFC00000
* (SWITCHER_ADDR). We might not get it in theory, but in practice
* it's worked so far. */
switcher_vma = __get_vm_area(TOTAL_SWITCHER_PAGES * PAGE_SIZE,
VM_ALLOC, SWITCHER_ADDR, VMALLOC_END);
if (!switcher_vma) {
err = -ENOMEM;
printk("lguest: could not map switcher pages high\n");
goto free_pages;
}
/* This code actually sets up the pages we've allocated to appear at
* SWITCHER_ADDR. map_vm_area() takes the vma we allocated above, the
* kind of pages we're mapping (kernel pages), and a pointer to our
* array of struct pages. It increments that pointer, but we don't
* care. */
pagep = switcher_page;
err = map_vm_area(switcher_vma, PAGE_KERNEL, &pagep);
if (err) {
printk("lguest: map_vm_area failed: %i\n", err);
goto free_vma;
}
/* Now the switcher is mapped at the right address, we can't fail!
* Copy in the compiled-in Switcher code (from switcher.S). */
memcpy(switcher_vma->addr, start_switcher_text,
end_switcher_text - start_switcher_text);
/* Most of the switcher.S doesn't care that it's been moved; on Intel,
* jumps are relative, and it doesn't access any references to external
* code or data.
*
* The only exception is the interrupt handlers in switcher.S: their
* addresses are placed in a table (default_idt_entries), so we need to
* update the table with the new addresses. switcher_offset() is a
* convenience function which returns the distance between the builtin
* switcher code and the high-mapped copy we just made. */
for (i = 0; i < IDT_ENTRIES; i++)
default_idt_entries[i] += switcher_offset();
/*
* Set up the Switcher's per-cpu areas.
*
* Each CPU gets two pages of its own within the high-mapped region
* (aka. "struct lguest_pages"). Much of this can be initialized now,
* but some depends on what Guest we are running (which is set up in
* copy_in_guest_info()).
*/
for_each_possible_cpu(i) {
/* lguest_pages() returns this CPU's two pages. */
struct lguest_pages *pages = lguest_pages(i);
/* This is a convenience pointer to make the code fit one
* statement to a line. */
struct lguest_ro_state *state = &pages->state;
/* The Global Descriptor Table: the Host has a different one
* for each CPU. We keep a descriptor for the GDT which says
* where it is and how big it is (the size is actually the last
* byte, not the size, hence the "-1"). */
state->host_gdt_desc.size = GDT_SIZE-1;
state->host_gdt_desc.address = (long)get_cpu_gdt_table(i);
/* All CPUs on the Host use the same Interrupt Descriptor
* Table, so we just use store_idt(), which gets this CPU's IDT
* descriptor. */
store_idt(&state->host_idt_desc);
/* The descriptors for the Guest's GDT and IDT can be filled
* out now, too. We copy the GDT & IDT into ->guest_gdt and
* ->guest_idt before actually running the Guest. */
state->guest_idt_desc.size = sizeof(state->guest_idt)-1;
state->guest_idt_desc.address = (long)&state->guest_idt;
state->guest_gdt_desc.size = sizeof(state->guest_gdt)-1;
state->guest_gdt_desc.address = (long)&state->guest_gdt;
/* We know where we want the stack to be when the Guest enters
* the switcher: in pages->regs. The stack grows upwards, so
* we start it at the end of that structure. */
state->guest_tss.esp0 = (long)(&pages->regs + 1);
/* And this is the GDT entry to use for the stack: we keep a
* couple of special LGUEST entries. */
state->guest_tss.ss0 = LGUEST_DS;
/* x86 can have a finegrained bitmap which indicates what I/O
* ports the process can use. We set it to the end of our
* structure, meaning "none". */
state->guest_tss.io_bitmap_base = sizeof(state->guest_tss);
/* Some GDT entries are the same across all Guests, so we can
* set them up now. */
setup_default_gdt_entries(state);
/* Most IDT entries are the same for all Guests, too.*/
setup_default_idt_entries(state, default_idt_entries);
/* The Host needs to be able to use the LGUEST segments on this
* CPU, too, so put them in the Host GDT. */
get_cpu_gdt_table(i)[GDT_ENTRY_LGUEST_CS] = FULL_EXEC_SEGMENT;
get_cpu_gdt_table(i)[GDT_ENTRY_LGUEST_DS] = FULL_SEGMENT;
}
/* In the Switcher, we want the %cs segment register to use the
* LGUEST_CS GDT entry: we've put that in the Host and Guest GDTs, so
* it will be undisturbed when we switch. To change %cs and jump we
* need this structure to feed to Intel's "lcall" instruction. */
lguest_entry.offset = (long)switch_to_guest + switcher_offset();
lguest_entry.segment = LGUEST_CS;
printk(KERN_INFO "lguest: mapped switcher at %p\n",
switcher_vma->addr);
/* And we succeeded... */
return 0;
free_vma:
vunmap(switcher_vma->addr);
free_pages:
i = TOTAL_SWITCHER_PAGES;
free_some_pages:
for (--i; i >= 0; i--)
__free_pages(switcher_page[i], 0);
kfree(switcher_page);
out:
return err;
}
/*:*/
/* Cleaning up the mapping when the module is unloaded is almost...
* too easy. */
static void unmap_switcher(void)
{
unsigned int i;
/* vunmap() undoes *both* map_vm_area() and __get_vm_area(). */
vunmap(switcher_vma->addr);
/* Now we just need to free the pages we copied the switcher into */
for (i = 0; i < TOTAL_SWITCHER_PAGES; i++)
__free_pages(switcher_page[i], 0);
}
/*H:130 Our Guest is usually so well behaved; it never tries to do things it
* isn't allowed to. Unfortunately, "struct paravirt_ops" isn't quite
* complete, because it doesn't contain replacements for the Intel I/O
* instructions. As a result, the Guest sometimes fumbles across one during
* the boot process as it probes for various things which are usually attached
* to a PC.
*
* When the Guest uses one of these instructions, we get trap #13 (General
* Protection Fault) and come here. We see if it's one of those troublesome
* instructions and skip over it. We return true if we did. */
static int emulate_insn(struct lguest *lg)
{
u8 insn;
unsigned int insnlen = 0, in = 0, shift = 0;
/* The eip contains the *virtual* address of the Guest's instruction:
* guest_pa just subtracts the Guest's page_offset. */
unsigned long physaddr = guest_pa(lg, lg->regs->eip);
/* The guest_pa() function only works for Guest kernel addresses, but
* that's all we're trying to do anyway. */
if (lg->regs->eip < lg->page_offset)
return 0;
/* Decoding x86 instructions is icky. */
lgread(lg, &insn, physaddr, 1);
/* 0x66 is an "operand prefix". It means it's using the upper 16 bits
of the eax register. */
if (insn == 0x66) {
shift = 16;
/* The instruction is 1 byte so far, read the next byte. */
insnlen = 1;
lgread(lg, &insn, physaddr + insnlen, 1);
}
/* We can ignore the lower bit for the moment and decode the 4 opcodes
* we need to emulate. */
switch (insn & 0xFE) {
case 0xE4: /* in <next byte>,%al */
insnlen += 2;
in = 1;
break;
case 0xEC: /* in (%dx),%al */
insnlen += 1;
in = 1;
break;
case 0xE6: /* out %al,<next byte> */
insnlen += 2;
break;
case 0xEE: /* out %al,(%dx) */
insnlen += 1;
break;
default:
/* OK, we don't know what this is, can't emulate. */
return 0;
}
/* If it was an "IN" instruction, they expect the result to be read
* into %eax, so we change %eax. We always return all-ones, which
* traditionally means "there's nothing there". */
if (in) {
/* Lower bit tells is whether it's a 16 or 32 bit access */
if (insn & 0x1)
lg->regs->eax = 0xFFFFFFFF;
else
lg->regs->eax |= (0xFFFF << shift);
}
/* Finally, we've "done" the instruction, so move past it. */
lg->regs->eip += insnlen;
/* Success! */
return 1;
}
/*:*/
/*L:305
* Dealing With Guest Memory.
*
* When the Guest gives us (what it thinks is) a physical address, we can use
* the normal copy_from_user() & copy_to_user() on that address: remember,
* Guest physical == Launcher virtual.
*
* But we can't trust the Guest: it might be trying to access the Launcher
* code. We have to check that the range is below the pfn_limit the Launcher
* gave us. We have to make sure that addr + len doesn't give us a false
* positive by overflowing, too. */
int lguest_address_ok(const struct lguest *lg,
unsigned long addr, unsigned long len)
{
return (addr+len) / PAGE_SIZE < lg->pfn_limit && (addr+len >= addr);
}
/* This is a convenient routine to get a 32-bit value from the Guest (a very
* common operation). Here we can see how useful the kill_lguest() routine we
* met in the Launcher can be: we return a random value (0) instead of needing
* to return an error. */
u32 lgread_u32(struct lguest *lg, unsigned long addr)
{
u32 val = 0;
/* Don't let them access lguest binary. */
if (!lguest_address_ok(lg, addr, sizeof(val))
|| get_user(val, (u32 __user *)addr) != 0)
kill_guest(lg, "bad read address %#lx", addr);
return val;
}
/* Same thing for writing a value. */
void lgwrite_u32(struct lguest *lg, unsigned long addr, u32 val)
{
if (!lguest_address_ok(lg, addr, sizeof(val))
|| put_user(val, (u32 __user *)addr) != 0)
kill_guest(lg, "bad write address %#lx", addr);
}
/* This routine is more generic, and copies a range of Guest bytes into a
* buffer. If the copy_from_user() fails, we fill the buffer with zeroes, so
* the caller doesn't end up using uninitialized kernel memory. */
void lgread(struct lguest *lg, void *b, unsigned long addr, unsigned bytes)
{
if (!lguest_address_ok(lg, addr, bytes)
|| copy_from_user(b, (void __user *)addr, bytes) != 0) {
/* copy_from_user should do this, but as we rely on it... */
memset(b, 0, bytes);
kill_guest(lg, "bad read address %#lx len %u", addr, bytes);
}
}
/* Similarly, our generic routine to copy into a range of Guest bytes. */
void lgwrite(struct lguest *lg, unsigned long addr, const void *b,
unsigned bytes)
{
if (!lguest_address_ok(lg, addr, bytes)
|| copy_to_user((void __user *)addr, b, bytes) != 0)
kill_guest(lg, "bad write address %#lx len %u", addr, bytes);
}
/* (end of memory access helper routines) :*/
static void set_ts(void)
{
u32 cr0;
cr0 = read_cr0();
if (!(cr0 & 8))
write_cr0(cr0|8);
}
/*S:010
* We are getting close to the Switcher.
*
* Remember that each CPU has two pages which are visible to the Guest when it
* runs on that CPU. This has to contain the state for that Guest: we copy the
* state in just before we run the Guest.
*
* Each Guest has "changed" flags which indicate what has changed in the Guest
* since it last ran. We saw this set in interrupts_and_traps.c and
* segments.c.
*/
static void copy_in_guest_info(struct lguest *lg, struct lguest_pages *pages)
{
/* Copying all this data can be quite expensive. We usually run the
* same Guest we ran last time (and that Guest hasn't run anywhere else
* meanwhile). If that's not the case, we pretend everything in the
* Guest has changed. */
if (__get_cpu_var(last_guest) != lg || lg->last_pages != pages) {
__get_cpu_var(last_guest) = lg;
lg->last_pages = pages;
lg->changed = CHANGED_ALL;
}
/* These copies are pretty cheap, so we do them unconditionally: */
/* Save the current Host top-level page directory. */
pages->state.host_cr3 = __pa(current->mm->pgd);
/* Set up the Guest's page tables to see this CPU's pages (and no
* other CPU's pages). */
map_switcher_in_guest(lg, pages);
/* Set up the two "TSS" members which tell the CPU what stack to use
* for traps which do directly into the Guest (ie. traps at privilege
* level 1). */
pages->state.guest_tss.esp1 = lg->esp1;
pages->state.guest_tss.ss1 = lg->ss1;
/* Copy direct-to-Guest trap entries. */
if (lg->changed & CHANGED_IDT)
copy_traps(lg, pages->state.guest_idt, default_idt_entries);
/* Copy all GDT entries which the Guest can change. */
if (lg->changed & CHANGED_GDT)
copy_gdt(lg, pages->state.guest_gdt);
/* If only the TLS entries have changed, copy them. */
else if (lg->changed & CHANGED_GDT_TLS)
copy_gdt_tls(lg, pages->state.guest_gdt);
/* Mark the Guest as unchanged for next time. */
lg->changed = 0;
}
/* Finally: the code to actually call into the Switcher to run the Guest. */
static void run_guest_once(struct lguest *lg, struct lguest_pages *pages)
{
/* This is a dummy value we need for GCC's sake. */
unsigned int clobber;
/* Copy the guest-specific information into this CPU's "struct
* lguest_pages". */
copy_in_guest_info(lg, pages);
/* Set the trap number to 256 (impossible value). If we fault while
* switching to the Guest (bad segment registers or bug), this will
* cause us to abort the Guest. */
lg->regs->trapnum = 256;
/* Now: we push the "eflags" register on the stack, then do an "lcall".
* This is how we change from using the kernel code segment to using
* the dedicated lguest code segment, as well as jumping into the
* Switcher.
*
* The lcall also pushes the old code segment (KERNEL_CS) onto the
* stack, then the address of this call. This stack layout happens to
* exactly match the stack of an interrupt... */
asm volatile("pushf; lcall *lguest_entry"
/* This is how we tell GCC that %eax ("a") and %ebx ("b")
* are changed by this routine. The "=" means output. */
: "=a"(clobber), "=b"(clobber)
/* %eax contains the pages pointer. ("0" refers to the
* 0-th argument above, ie "a"). %ebx contains the
* physical address of the Guest's top-level page
* directory. */
: "0"(pages), "1"(__pa(lg->pgdirs[lg->pgdidx].pgdir))
/* We tell gcc that all these registers could change,
* which means we don't have to save and restore them in
* the Switcher. */
: "memory", "%edx", "%ecx", "%edi", "%esi");
}
/*:*/
/*H:030 Let's jump straight to the the main loop which runs the Guest.
* Remember, this is called by the Launcher reading /dev/lguest, and we keep
* going around and around until something interesting happens. */
int run_guest(struct lguest *lg, unsigned long __user *user)
{
/* We stop running once the Guest is dead. */
while (!lg->dead) {
/* We need to initialize this, otherwise gcc complains. It's
* not (yet) clever enough to see that it's initialized when we
* need it. */
unsigned int cr2 = 0; /* Damn gcc */
/* First we run any hypercalls the Guest wants done: either in
* the hypercall ring in "struct lguest_data", or directly by
* using int 31 (LGUEST_TRAP_ENTRY). */
do_hypercalls(lg);
/* It's possible the Guest did a SEND_DMA hypercall to the
* Launcher, in which case we return from the read() now. */
if (lg->dma_is_pending) {
if (put_user(lg->pending_dma, user) ||
put_user(lg->pending_key, user+1))
return -EFAULT;
return sizeof(unsigned long)*2;
}
/* Check for signals */
if (signal_pending(current))
return -ERESTARTSYS;
/* If Waker set break_out, return to Launcher. */
if (lg->break_out)
return -EAGAIN;
/* Check if there are any interrupts which can be delivered
* now: if so, this sets up the hander to be executed when we
* next run the Guest. */
maybe_do_interrupt(lg);
/* All long-lived kernel loops need to check with this horrible
* thing called the freezer. If the Host is trying to suspend,
* it stops us. */
try_to_freeze();
/* Just make absolutely sure the Guest is still alive. One of
* those hypercalls could have been fatal, for example. */
if (lg->dead)
break;
/* If the Guest asked to be stopped, we sleep. The Guest's
* clock timer or LHCALL_BREAK from the Waker will wake us. */
if (lg->halted) {
set_current_state(TASK_INTERRUPTIBLE);
schedule();
continue;
}
/* OK, now we're ready to jump into the Guest. First we put up
* the "Do Not Disturb" sign: */
local_irq_disable();
/* Remember the awfully-named TS bit? If the Guest has asked
* to set it we set it now, so we can trap and pass that trap
* to the Guest if it uses the FPU. */
if (lg->ts)
set_ts();
/* SYSENTER is an optimized way of doing system calls. We
* can't allow it because it always jumps to privilege level 0.
* A normal Guest won't try it because we don't advertise it in
* CPUID, but a malicious Guest (or malicious Guest userspace
* program) could, so we tell the CPU to disable it before
* running the Guest. */
if (boot_cpu_has(X86_FEATURE_SEP))
wrmsr(MSR_IA32_SYSENTER_CS, 0, 0);
/* Now we actually run the Guest. It will pop back out when
* something interesting happens, and we can examine its
* registers to see what it was doing. */
run_guest_once(lg, lguest_pages(raw_smp_processor_id()));
/* The "regs" pointer contains two extra entries which are not
* really registers: a trap number which says what interrupt or
* trap made the switcher code come back, and an error code
* which some traps set. */
/* If the Guest page faulted, then the cr2 register will tell
* us the bad virtual address. We have to grab this now,
* because once we re-enable interrupts an interrupt could
* fault and thus overwrite cr2, or we could even move off to a
* different CPU. */
if (lg->regs->trapnum == 14)
cr2 = read_cr2();
/* Similarly, if we took a trap because the Guest used the FPU,
* we have to restore the FPU it expects to see. */
else if (lg->regs->trapnum == 7)
math_state_restore();
/* Restore SYSENTER if it's supposed to be on. */
if (boot_cpu_has(X86_FEATURE_SEP))
wrmsr(MSR_IA32_SYSENTER_CS, __KERNEL_CS, 0);
/* Now we're ready to be interrupted or moved to other CPUs */
local_irq_enable();
/* OK, so what happened? */
switch (lg->regs->trapnum) {
case 13: /* We've intercepted a GPF. */
/* Check if this was one of those annoying IN or OUT
* instructions which we need to emulate. If so, we
* just go back into the Guest after we've done it. */
if (lg->regs->errcode == 0) {
if (emulate_insn(lg))
continue;
}
break;
case 14: /* We've intercepted a page fault. */
/* The Guest accessed a virtual address that wasn't
* mapped. This happens a lot: we don't actually set
* up most of the page tables for the Guest at all when
* we start: as it runs it asks for more and more, and
* we set them up as required. In this case, we don't
* even tell the Guest that the fault happened.
*
* The errcode tells whether this was a read or a
* write, and whether kernel or userspace code. */
if (demand_page(lg, cr2, lg->regs->errcode))
continue;
/* OK, it's really not there (or not OK): the Guest
* needs to know. We write out the cr2 value so it
* knows where the fault occurred.
*
* Note that if the Guest were really messed up, this
* could happen before it's done the INITIALIZE
* hypercall, so lg->lguest_data will be NULL, so
* &lg->lguest_data->cr2 will be address 8. Writing
* into that address won't hurt the Host at all,
* though. */
if (put_user(cr2, &lg->lguest_data->cr2))
kill_guest(lg, "Writing cr2");
break;
case 7: /* We've intercepted a Device Not Available fault. */
/* If the Guest doesn't want to know, we already
* restored the Floating Point Unit, so we just
* continue without telling it. */
if (!lg->ts)
continue;
break;
case 32 ... 255:
/* These values mean a real interrupt occurred, in
* which case the Host handler has already been run.
* We just do a friendly check if another process
* should now be run, then fall through to loop
* around: */
cond_resched();
case LGUEST_TRAP_ENTRY: /* Handled at top of loop */
continue;
}
/* If we get here, it's a trap the Guest wants to know
* about. */
if (deliver_trap(lg, lg->regs->trapnum))
continue;
/* If the Guest doesn't have a handler (either it hasn't
* registered any yet, or it's one of the faults we don't let
* it handle), it dies with a cryptic error message. */
kill_guest(lg, "unhandled trap %li at %#lx (%#lx)",
lg->regs->trapnum, lg->regs->eip,
lg->regs->trapnum == 14 ? cr2 : lg->regs->errcode);
}
/* The Guest is dead => "No such file or directory" */
return -ENOENT;
}
/* Now we can look at each of the routines this calls, in increasing order of
* complexity: do_hypercalls(), emulate_insn(), maybe_do_interrupt(),
* deliver_trap() and demand_page(). After all those, we'll be ready to
* examine the Switcher, and our philosophical understanding of the Host/Guest
* duality will be complete. :*/
int find_free_guest(void)
{
unsigned int i;
for (i = 0; i < MAX_LGUEST_GUESTS; i++)
if (!lguests[i].tsk)
return i;
return -1;
}
static void adjust_pge(void *on)
{
if (on)
write_cr4(read_cr4() | X86_CR4_PGE);
else
write_cr4(read_cr4() & ~X86_CR4_PGE);
}
/*H:000
* Welcome to the Host!
*
* By this point your brain has been tickled by the Guest code and numbed by
* the Launcher code; prepare for it to be stretched by the Host code. This is
* the heart. Let's begin at the initialization routine for the Host's lg
* module.
*/
static int __init init(void)
{
int err;
/* Lguest can't run under Xen, VMI or itself. It does Tricky Stuff. */
if (paravirt_enabled()) {
printk("lguest is afraid of %s\n", paravirt_ops.name);
return -EPERM;
}
/* First we put the Switcher up in very high virtual memory. */
err = map_switcher();
if (err)
return err;
/* Now we set up the pagetable implementation for the Guests. */
err = init_pagetables(switcher_page, SHARED_SWITCHER_PAGES);
if (err) {
unmap_switcher();
return err;
}
/* The I/O subsystem needs some things initialized. */
lguest_io_init();
/* /dev/lguest needs to be registered. */
err = lguest_device_init();
if (err) {
free_pagetables();
unmap_switcher();
return err;
}
/* Finally, we need to turn off "Page Global Enable". PGE is an
* optimization where page table entries are specially marked to show
* they never change. The Host kernel marks all the kernel pages this
* way because it's always present, even when userspace is running.
*
* Lguest breaks this: unbeknownst to the rest of the Host kernel, we
* switch to the Guest kernel. If you don't disable this on all CPUs,
* you'll get really weird bugs that you'll chase for two days.
*
* I used to turn PGE off every time we switched to the Guest and back
* on when we return, but that slowed the Switcher down noticibly. */
/* We don't need the complexity of CPUs coming and going while we're
* doing this. */
lock_cpu_hotplug();
if (cpu_has_pge) { /* We have a broader idea of "global". */
/* Remember that this was originally set (for cleanup). */
cpu_had_pge = 1;
/* adjust_pge is a helper function which sets or unsets the PGE
* bit on its CPU, depending on the argument (0 == unset). */
on_each_cpu(adjust_pge, (void *)0, 0, 1);
/* Turn off the feature in the global feature set. */
clear_bit(X86_FEATURE_PGE, boot_cpu_data.x86_capability);
}
unlock_cpu_hotplug();
/* All good! */
return 0;
}
/* Cleaning up is just the same code, backwards. With a little French. */
static void __exit fini(void)
{
lguest_device_remove();
free_pagetables();
unmap_switcher();
/* If we had PGE before we started, turn it back on now. */
lock_cpu_hotplug();
if (cpu_had_pge) {
set_bit(X86_FEATURE_PGE, boot_cpu_data.x86_capability);
/* adjust_pge's argument "1" means set PGE. */
on_each_cpu(adjust_pge, (void *)1, 0, 1);
}
unlock_cpu_hotplug();
}
/* The Host side of lguest can be a module. This is a nice way for people to
* play with it. */
module_init(init);
module_exit(fini);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.com.au>");
