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/*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 <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. */

DEFINE_MUTEX(lguest_lock);

/*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"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 <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",

               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:032

 * 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 lguest *lg, void *b, unsigned long addr, unsigned bytes)

{

        if (!lguest_address_ok(lg, addr, bytes)

            || copy_from_user(b, lg->mem_base + 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);

        }

}

/* This is the write (copy into guest) version. */

void __lgwrite(struct lguest *lg, unsigned long addr, const void *b,

               unsigned bytes)

{

        if (!lguest_address_ok(lg, addr, bytes)

            || copy_to_user(lg->mem_base + addr, b, bytes) != 0)

                kill_guest(lg, "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 lguest *lg, unsigned long __user *user)

{

        /* We stop running once the Guest is dead. */

        while (!lg->dead) {

                /* First we run any hypercalls the Guest wants done. */

                if (lg->hcall)

                        do_hypercalls(lg);

                /* It's possible the Guest did a NOTIFY hypercall to the

                 * Launcher, in which case we return from the read() now. */

                if (lg->pending_notify) {

                        if (put_user(lg->pending_notify, user))

                                return -EFAULT;

                        return sizeof(lg->pending_notify);

                }

                /* 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();

                /* Actually run the Guest until something happens. */

                lguest_arch_run_guest(lg);

                /* Now we're ready to be interrupted or moved to other CPUs */

                local_irq_enable();

                /* Now we deal with whatever happened to the Guest. */

                lguest_arch_handle_trap(lg);

        }

        /* The Guest is dead => "No such file or directory" */

        return -ENOENT;

}

/*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", pv_info.name);

                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. */

        lguest_arch_host_init();

        /* All good! */

        return 0;

free_interrupts:

        free_interrupts();

free_pgtables:

        free_pagetables();

unmap:

        unmap_switcher();

out:

        return err;

}

/* Cleaning up is just the same code, backwards.  With a little French. */

static void __exit fini(void)

{

        lguest_device_remove();

        free_interrupts();

        free_pagetables();

        unmap_switcher();

        lguest_arch_host_fini();

}

/*:*/

/* 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>");