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a6bd8e1303
Took some cycles to re-read the Lguest Journey end-to-end, fix some rot and tighten some phrases. Only comments change. No new jokes, but a couple of recycled old jokes. Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
327 lines
9.8 KiB
C
327 lines
9.8 KiB
C
/*P:400 This contains run_guest() which actually calls into the Host<->Guest
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* Switcher and analyzes the return, such as determining if the Guest wants the
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* Host to do something. This file also contains useful helper routines. :*/
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#include <linux/module.h>
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#include <linux/stringify.h>
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#include <linux/stddef.h>
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#include <linux/io.h>
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#include <linux/mm.h>
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#include <linux/vmalloc.h>
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#include <linux/cpu.h>
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#include <linux/freezer.h>
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#include <linux/highmem.h>
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#include <asm/paravirt.h>
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#include <asm/pgtable.h>
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#include <asm/uaccess.h>
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#include <asm/poll.h>
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#include <asm/asm-offsets.h>
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#include "lg.h"
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static struct vm_struct *switcher_vma;
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static struct page **switcher_page;
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/* This One Big lock protects all inter-guest data structures. */
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DEFINE_MUTEX(lguest_lock);
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/*H:010 We need to set up the Switcher at a high virtual address. Remember the
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* Switcher is a few hundred bytes of assembler code which actually changes the
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* CPU to run the Guest, and then changes back to the Host when a trap or
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* interrupt happens.
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*
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* The Switcher code must be at the same virtual address in the Guest as the
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* Host since it will be running as the switchover occurs.
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*
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* Trying to map memory at a particular address is an unusual thing to do, so
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* it's not a simple one-liner. */
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static __init int map_switcher(void)
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{
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int i, err;
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struct page **pagep;
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/*
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* Map the Switcher in to high memory.
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*
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* It turns out that if we choose the address 0xFFC00000 (4MB under the
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* top virtual address), it makes setting up the page tables really
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* easy.
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*/
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/* We allocate an array of struct page pointers. map_vm_area() wants
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* this, rather than just an array of pages. */
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switcher_page = kmalloc(sizeof(switcher_page[0])*TOTAL_SWITCHER_PAGES,
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GFP_KERNEL);
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if (!switcher_page) {
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err = -ENOMEM;
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goto out;
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}
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/* Now we actually allocate the pages. The Guest will see these pages,
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* so we make sure they're zeroed. */
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for (i = 0; i < TOTAL_SWITCHER_PAGES; i++) {
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unsigned long addr = get_zeroed_page(GFP_KERNEL);
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if (!addr) {
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err = -ENOMEM;
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goto free_some_pages;
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}
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switcher_page[i] = virt_to_page(addr);
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}
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/* First we check that the Switcher won't overlap the fixmap area at
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* the top of memory. It's currently nowhere near, but it could have
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* very strange effects if it ever happened. */
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if (SWITCHER_ADDR + (TOTAL_SWITCHER_PAGES+1)*PAGE_SIZE > FIXADDR_START){
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err = -ENOMEM;
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printk("lguest: mapping switcher would thwack fixmap\n");
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goto free_pages;
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}
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/* Now we reserve the "virtual memory area" we want: 0xFFC00000
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* (SWITCHER_ADDR). We might not get it in theory, but in practice
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* it's worked so far. The end address needs +1 because __get_vm_area
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* allocates an extra guard page, so we need space for that. */
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switcher_vma = __get_vm_area(TOTAL_SWITCHER_PAGES * PAGE_SIZE,
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VM_ALLOC, SWITCHER_ADDR, SWITCHER_ADDR
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+ (TOTAL_SWITCHER_PAGES+1) * PAGE_SIZE);
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if (!switcher_vma) {
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err = -ENOMEM;
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printk("lguest: could not map switcher pages high\n");
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goto free_pages;
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}
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/* This code actually sets up the pages we've allocated to appear at
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* SWITCHER_ADDR. map_vm_area() takes the vma we allocated above, the
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* kind of pages we're mapping (kernel pages), and a pointer to our
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* array of struct pages. It increments that pointer, but we don't
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* care. */
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pagep = switcher_page;
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err = map_vm_area(switcher_vma, PAGE_KERNEL, &pagep);
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if (err) {
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printk("lguest: map_vm_area failed: %i\n", err);
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goto free_vma;
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}
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/* Now the Switcher is mapped at the right address, we can't fail!
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* Copy in the compiled-in Switcher code (from <arch>_switcher.S). */
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memcpy(switcher_vma->addr, start_switcher_text,
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end_switcher_text - start_switcher_text);
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printk(KERN_INFO "lguest: mapped switcher at %p\n",
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switcher_vma->addr);
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/* And we succeeded... */
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return 0;
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free_vma:
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vunmap(switcher_vma->addr);
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free_pages:
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i = TOTAL_SWITCHER_PAGES;
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free_some_pages:
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for (--i; i >= 0; i--)
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__free_pages(switcher_page[i], 0);
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kfree(switcher_page);
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out:
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return err;
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}
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/*:*/
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/* Cleaning up the mapping when the module is unloaded is almost...
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* too easy. */
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static void unmap_switcher(void)
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{
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unsigned int i;
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/* vunmap() undoes *both* map_vm_area() and __get_vm_area(). */
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vunmap(switcher_vma->addr);
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/* Now we just need to free the pages we copied the switcher into */
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for (i = 0; i < TOTAL_SWITCHER_PAGES; i++)
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__free_pages(switcher_page[i], 0);
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}
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/*H:032
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* Dealing With Guest Memory.
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*
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* Before we go too much further into the Host, we need to grok the routines
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* we use to deal with Guest memory.
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*
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* When the Guest gives us (what it thinks is) a physical address, we can use
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* the normal copy_from_user() & copy_to_user() on the corresponding place in
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* the memory region allocated by the Launcher.
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*
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* But we can't trust the Guest: it might be trying to access the Launcher
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* code. We have to check that the range is below the pfn_limit the Launcher
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* gave us. We have to make sure that addr + len doesn't give us a false
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* positive by overflowing, too. */
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int lguest_address_ok(const struct lguest *lg,
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unsigned long addr, unsigned long len)
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{
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return (addr+len) / PAGE_SIZE < lg->pfn_limit && (addr+len >= addr);
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}
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/* This routine copies memory from the Guest. Here we can see how useful the
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* kill_lguest() routine we met in the Launcher can be: we return a random
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* value (all zeroes) instead of needing to return an error. */
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void __lgread(struct lg_cpu *cpu, void *b, unsigned long addr, unsigned bytes)
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{
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if (!lguest_address_ok(cpu->lg, addr, bytes)
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|| copy_from_user(b, cpu->lg->mem_base + addr, bytes) != 0) {
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/* copy_from_user should do this, but as we rely on it... */
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memset(b, 0, bytes);
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kill_guest(cpu, "bad read address %#lx len %u", addr, bytes);
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}
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}
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/* This is the write (copy into Guest) version. */
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void __lgwrite(struct lg_cpu *cpu, unsigned long addr, const void *b,
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unsigned bytes)
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{
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if (!lguest_address_ok(cpu->lg, addr, bytes)
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|| copy_to_user(cpu->lg->mem_base + addr, b, bytes) != 0)
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kill_guest(cpu, "bad write address %#lx len %u", addr, bytes);
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}
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/*:*/
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/*H:030 Let's jump straight to the the main loop which runs the Guest.
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* Remember, this is called by the Launcher reading /dev/lguest, and we keep
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* going around and around until something interesting happens. */
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int run_guest(struct lg_cpu *cpu, unsigned long __user *user)
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{
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/* We stop running once the Guest is dead. */
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while (!cpu->lg->dead) {
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/* First we run any hypercalls the Guest wants done. */
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if (cpu->hcall)
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do_hypercalls(cpu);
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/* It's possible the Guest did a NOTIFY hypercall to the
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* Launcher, in which case we return from the read() now. */
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if (cpu->pending_notify) {
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if (put_user(cpu->pending_notify, user))
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return -EFAULT;
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return sizeof(cpu->pending_notify);
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}
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/* Check for signals */
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if (signal_pending(current))
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return -ERESTARTSYS;
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/* If Waker set break_out, return to Launcher. */
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if (cpu->break_out)
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return -EAGAIN;
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/* Check if there are any interrupts which can be delivered now:
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* if so, this sets up the hander to be executed when we next
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* run the Guest. */
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maybe_do_interrupt(cpu);
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/* All long-lived kernel loops need to check with this horrible
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* thing called the freezer. If the Host is trying to suspend,
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* it stops us. */
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try_to_freeze();
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/* Just make absolutely sure the Guest is still alive. One of
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* those hypercalls could have been fatal, for example. */
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if (cpu->lg->dead)
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break;
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/* If the Guest asked to be stopped, we sleep. The Guest's
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* clock timer or LHCALL_BREAK from the Waker will wake us. */
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if (cpu->halted) {
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set_current_state(TASK_INTERRUPTIBLE);
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schedule();
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continue;
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}
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/* OK, now we're ready to jump into the Guest. First we put up
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* the "Do Not Disturb" sign: */
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local_irq_disable();
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/* Actually run the Guest until something happens. */
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lguest_arch_run_guest(cpu);
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/* Now we're ready to be interrupted or moved to other CPUs */
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local_irq_enable();
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/* Now we deal with whatever happened to the Guest. */
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lguest_arch_handle_trap(cpu);
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}
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/* Special case: Guest is 'dead' but wants a reboot. */
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if (cpu->lg->dead == ERR_PTR(-ERESTART))
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return -ERESTART;
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/* The Guest is dead => "No such file or directory" */
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return -ENOENT;
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}
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/*H:000
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* Welcome to the Host!
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*
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* By this point your brain has been tickled by the Guest code and numbed by
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* the Launcher code; prepare for it to be stretched by the Host code. This is
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* the heart. Let's begin at the initialization routine for the Host's lg
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* module.
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*/
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static int __init init(void)
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{
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int err;
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/* Lguest can't run under Xen, VMI or itself. It does Tricky Stuff. */
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if (paravirt_enabled()) {
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printk("lguest is afraid of being a guest\n");
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return -EPERM;
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}
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/* First we put the Switcher up in very high virtual memory. */
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err = map_switcher();
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if (err)
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goto out;
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/* Now we set up the pagetable implementation for the Guests. */
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err = init_pagetables(switcher_page, SHARED_SWITCHER_PAGES);
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if (err)
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goto unmap;
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/* We might need to reserve an interrupt vector. */
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err = init_interrupts();
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if (err)
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goto free_pgtables;
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/* /dev/lguest needs to be registered. */
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err = lguest_device_init();
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if (err)
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goto free_interrupts;
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/* Finally we do some architecture-specific setup. */
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lguest_arch_host_init();
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/* All good! */
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return 0;
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free_interrupts:
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free_interrupts();
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free_pgtables:
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free_pagetables();
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unmap:
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unmap_switcher();
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out:
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return err;
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}
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/* Cleaning up is just the same code, backwards. With a little French. */
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static void __exit fini(void)
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{
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lguest_device_remove();
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free_interrupts();
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free_pagetables();
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unmap_switcher();
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lguest_arch_host_fini();
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}
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/*:*/
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/* The Host side of lguest can be a module. This is a nice way for people to
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* play with it. */
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module_init(init);
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module_exit(fini);
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MODULE_LICENSE("GPL");
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MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.com.au>");
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