blob: 90663e01a56e0d4544b944da2fd81e5052a05a2f [file] [log] [blame]
/*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. :*/
#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 <linux/highmem.h>
#include <asm/paravirt.h>
#include <asm/pgtable.h>
#include <asm/uaccess.h>
#include <asm/poll.h>
#include <asm/asm-offsets.h>
#include "lg.h"
static struct vm_struct *switcher_vma;
static struct page **switcher_page;
/* This One Big lock protects all inter-guest data structures. */
/*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. */
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 pointers. map_vm_area() wants
* this, rather than just an array of pages. */
switcher_page = kmalloc(sizeof(switcher_page[0])*TOTAL_SWITCHER_PAGES,
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);
/* First we check that the Switcher won't overlap the fixmap area at
* the top of memory. It's currently nowhere near, but it could have
* very strange effects if it ever happened. */
err = -ENOMEM;
printk("lguest: mapping switcher would thwack fixmap\n");
goto free_pages;
/* 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. The end address needs +1 because __get_vm_area
* allocates an extra guard page, so we need space for that. */
switcher_vma = __get_vm_area(TOTAL_SWITCHER_PAGES * PAGE_SIZE,
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 <arch>_switcher.S). */
memcpy(switcher_vma->addr, start_switcher_text,
end_switcher_text - start_switcher_text);
printk(KERN_INFO "lguest: mapped switcher at %p\n",
/* And we succeeded... */
return 0;
for (--i; i >= 0; i--)
__free_pages(switcher_page[i], 0);
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(). */
/* 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);
* Dealing With Guest Memory.
* Before we go too much further into the Host, we need to grok the routines
* we use to deal 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 the corresponding place in
* the memory region allocated by the Launcher.
* 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 routine copies memory from the Guest. Here we can see how useful the
* kill_lguest() routine we met in the Launcher can be: we return a random
* value (all zeroes) instead of needing to return an error. */
void __lgread(struct lg_cpu *cpu, void *b, unsigned long addr, unsigned bytes)
if (!lguest_address_ok(cpu->lg, addr, bytes)
|| copy_from_user(b, cpu->lg->mem_base + addr, bytes) != 0) {
/* copy_from_user should do this, but as we rely on it... */
memset(b, 0, bytes);
kill_guest(cpu, "bad read address %#lx len %u", addr, bytes);
/* This is the write (copy into Guest) version. */
void __lgwrite(struct lg_cpu *cpu, unsigned long addr, const void *b,
unsigned bytes)
if (!lguest_address_ok(cpu->lg, addr, bytes)
|| copy_to_user(cpu->lg->mem_base + addr, b, bytes) != 0)
kill_guest(cpu, "bad write address %#lx len %u", addr, bytes);
/*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 lg_cpu *cpu, unsigned long __user *user)
/* We stop running once the Guest is dead. */
while (!cpu->lg->dead) {
/* First we run any hypercalls the Guest wants done. */
if (cpu->hcall)
/* It's possible the Guest did a NOTIFY hypercall to the
* Launcher, in which case we return from the read() now. */
if (cpu->pending_notify) {
if (put_user(cpu->pending_notify, user))
return -EFAULT;
return sizeof(cpu->pending_notify);
/* Check for signals */
if (signal_pending(current))
/* If Waker set break_out, return to Launcher. */
if (cpu->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. */
/* 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. */
/* Just make absolutely sure the Guest is still alive. One of
* those hypercalls could have been fatal, for example. */
if (cpu->lg->dead)
/* If the Guest asked to be stopped, we sleep. The Guest's
* clock timer or LHCALL_BREAK from the Waker will wake us. */
if (cpu->halted) {
/* OK, now we're ready to jump into the Guest. First we put up
* the "Do Not Disturb" sign: */
/* Actually run the Guest until something happens. */
/* Now we're ready to be interrupted or moved to other CPUs */
/* Now we deal with whatever happened to the Guest. */
/* Special case: Guest is 'dead' but wants a reboot. */
if (cpu->lg->dead == ERR_PTR(-ERESTART))
return -ERESTART;
/* The Guest is dead => "No such file or directory" */
return -ENOENT;
* 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 being a guest\n");
return -EPERM;
/* First we put the Switcher up in very high virtual memory. */
err = map_switcher();
if (err)
goto out;
/* Now we set up the pagetable implementation for the Guests. */
err = init_pagetables(switcher_page, SHARED_SWITCHER_PAGES);
if (err)
goto unmap;
/* We might need to reserve an interrupt vector. */
err = init_interrupts();
if (err)
goto free_pgtables;
/* /dev/lguest needs to be registered. */
err = lguest_device_init();
if (err)
goto free_interrupts;
/* Finally we do some architecture-specific setup. */
/* All good! */
return 0;
return err;
/* Cleaning up is just the same code, backwards. With a little French. */
static void __exit fini(void)
/* The Host side of lguest can be a module. This is a nice way for people to
* play with it. */
MODULE_AUTHOR("Rusty Russell <>");