linux/drivers/lguest/core.c
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   1/*P:400
   2 * This contains run_guest() which actually calls into the Host<->Guest
   3 * Switcher and analyzes the return, such as determining if the Guest wants the
   4 * Host to do something.  This file also contains useful helper routines.
   5:*/
   6#include <linux/module.h>
   7#include <linux/stringify.h>
   8#include <linux/stddef.h>
   9#include <linux/io.h>
  10#include <linux/mm.h>
  11#include <linux/vmalloc.h>
  12#include <linux/cpu.h>
  13#include <linux/freezer.h>
  14#include <linux/highmem.h>
  15#include <linux/slab.h>
  16#include <asm/paravirt.h>
  17#include <asm/pgtable.h>
  18#include <asm/uaccess.h>
  19#include <asm/poll.h>
  20#include <asm/asm-offsets.h>
  21#include "lg.h"
  22
  23unsigned long switcher_addr;
  24struct page **lg_switcher_pages;
  25static struct vm_struct *switcher_vma;
  26
  27/* This One Big lock protects all inter-guest data structures. */
  28DEFINE_MUTEX(lguest_lock);
  29
  30/*H:010
  31 * We need to set up the Switcher at a high virtual address.  Remember the
  32 * Switcher is a few hundred bytes of assembler code which actually changes the
  33 * CPU to run the Guest, and then changes back to the Host when a trap or
  34 * interrupt happens.
  35 *
  36 * The Switcher code must be at the same virtual address in the Guest as the
  37 * Host since it will be running as the switchover occurs.
  38 *
  39 * Trying to map memory at a particular address is an unusual thing to do, so
  40 * it's not a simple one-liner.
  41 */
  42static __init int map_switcher(void)
  43{
  44        int i, err;
  45        struct page **pagep;
  46
  47        /*
  48         * Map the Switcher in to high memory.
  49         *
  50         * It turns out that if we choose the address 0xFFC00000 (4MB under the
  51         * top virtual address), it makes setting up the page tables really
  52         * easy.
  53         */
  54
  55        /* We assume Switcher text fits into a single page. */
  56        if (end_switcher_text - start_switcher_text > PAGE_SIZE) {
  57                printk(KERN_ERR "lguest: switcher text too large (%zu)\n",
  58                       end_switcher_text - start_switcher_text);
  59                return -EINVAL;
  60        }
  61
  62        /*
  63         * We allocate an array of struct page pointers.  map_vm_area() wants
  64         * this, rather than just an array of pages.
  65         */
  66        lg_switcher_pages = kmalloc(sizeof(lg_switcher_pages[0])
  67                                    * TOTAL_SWITCHER_PAGES,
  68                                    GFP_KERNEL);
  69        if (!lg_switcher_pages) {
  70                err = -ENOMEM;
  71                goto out;
  72        }
  73
  74        /*
  75         * Now we actually allocate the pages.  The Guest will see these pages,
  76         * so we make sure they're zeroed.
  77         */
  78        for (i = 0; i < TOTAL_SWITCHER_PAGES; i++) {
  79                lg_switcher_pages[i] = alloc_page(GFP_KERNEL|__GFP_ZERO);
  80                if (!lg_switcher_pages[i]) {
  81                        err = -ENOMEM;
  82                        goto free_some_pages;
  83                }
  84        }
  85
  86        /*
  87         * We place the Switcher underneath the fixmap area, which is the
  88         * highest virtual address we can get.  This is important, since we
  89         * tell the Guest it can't access this memory, so we want its ceiling
  90         * as high as possible.
  91         */
  92        switcher_addr = FIXADDR_START - (TOTAL_SWITCHER_PAGES+1)*PAGE_SIZE;
  93
  94        /*
  95         * Now we reserve the "virtual memory area" we want.  We might
  96         * not get it in theory, but in practice it's worked so far.
  97         * The end address needs +1 because __get_vm_area allocates an
  98         * extra guard page, so we need space for that.
  99         */
 100        switcher_vma = __get_vm_area(TOTAL_SWITCHER_PAGES * PAGE_SIZE,
 101                                     VM_ALLOC, switcher_addr, switcher_addr
 102                                     + (TOTAL_SWITCHER_PAGES+1) * PAGE_SIZE);
 103        if (!switcher_vma) {
 104                err = -ENOMEM;
 105                printk("lguest: could not map switcher pages high\n");
 106                goto free_pages;
 107        }
 108
 109        /*
 110         * This code actually sets up the pages we've allocated to appear at
 111         * switcher_addr.  map_vm_area() takes the vma we allocated above, the
 112         * kind of pages we're mapping (kernel pages), and a pointer to our
 113         * array of struct pages.  It increments that pointer, but we don't
 114         * care.
 115         */
 116        pagep = lg_switcher_pages;
 117        err = map_vm_area(switcher_vma, PAGE_KERNEL_EXEC, &pagep);
 118        if (err) {
 119                printk("lguest: map_vm_area failed: %i\n", err);
 120                goto free_vma;
 121        }
 122
 123        /*
 124         * Now the Switcher is mapped at the right address, we can't fail!
 125         * Copy in the compiled-in Switcher code (from x86/switcher_32.S).
 126         */
 127        memcpy(switcher_vma->addr, start_switcher_text,
 128               end_switcher_text - start_switcher_text);
 129
 130        printk(KERN_INFO "lguest: mapped switcher at %p\n",
 131               switcher_vma->addr);
 132        /* And we succeeded... */
 133        return 0;
 134
 135free_vma:
 136        vunmap(switcher_vma->addr);
 137free_pages:
 138        i = TOTAL_SWITCHER_PAGES;
 139free_some_pages:
 140        for (--i; i >= 0; i--)
 141                __free_pages(lg_switcher_pages[i], 0);
 142        kfree(lg_switcher_pages);
 143out:
 144        return err;
 145}
 146/*:*/
 147
 148/* Cleaning up the mapping when the module is unloaded is almost... too easy. */
 149static void unmap_switcher(void)
 150{
 151        unsigned int i;
 152
 153        /* vunmap() undoes *both* map_vm_area() and __get_vm_area(). */
 154        vunmap(switcher_vma->addr);
 155        /* Now we just need to free the pages we copied the switcher into */
 156        for (i = 0; i < TOTAL_SWITCHER_PAGES; i++)
 157                __free_pages(lg_switcher_pages[i], 0);
 158        kfree(lg_switcher_pages);
 159}
 160
 161/*H:032
 162 * Dealing With Guest Memory.
 163 *
 164 * Before we go too much further into the Host, we need to grok the routines
 165 * we use to deal with Guest memory.
 166 *
 167 * When the Guest gives us (what it thinks is) a physical address, we can use
 168 * the normal copy_from_user() & copy_to_user() on the corresponding place in
 169 * the memory region allocated by the Launcher.
 170 *
 171 * But we can't trust the Guest: it might be trying to access the Launcher
 172 * code.  We have to check that the range is below the pfn_limit the Launcher
 173 * gave us.  We have to make sure that addr + len doesn't give us a false
 174 * positive by overflowing, too.
 175 */
 176bool lguest_address_ok(const struct lguest *lg,
 177                       unsigned long addr, unsigned long len)
 178{
 179        return (addr+len) / PAGE_SIZE < lg->pfn_limit && (addr+len >= addr);
 180}
 181
 182/*
 183 * This routine copies memory from the Guest.  Here we can see how useful the
 184 * kill_lguest() routine we met in the Launcher can be: we return a random
 185 * value (all zeroes) instead of needing to return an error.
 186 */
 187void __lgread(struct lg_cpu *cpu, void *b, unsigned long addr, unsigned bytes)
 188{
 189        if (!lguest_address_ok(cpu->lg, addr, bytes)
 190            || copy_from_user(b, cpu->lg->mem_base + addr, bytes) != 0) {
 191                /* copy_from_user should do this, but as we rely on it... */
 192                memset(b, 0, bytes);
 193                kill_guest(cpu, "bad read address %#lx len %u", addr, bytes);
 194        }
 195}
 196
 197/* This is the write (copy into Guest) version. */
 198void __lgwrite(struct lg_cpu *cpu, unsigned long addr, const void *b,
 199               unsigned bytes)
 200{
 201        if (!lguest_address_ok(cpu->lg, addr, bytes)
 202            || copy_to_user(cpu->lg->mem_base + addr, b, bytes) != 0)
 203                kill_guest(cpu, "bad write address %#lx len %u", addr, bytes);
 204}
 205/*:*/
 206
 207/*H:030
 208 * Let's jump straight to the the main loop which runs the Guest.
 209 * Remember, this is called by the Launcher reading /dev/lguest, and we keep
 210 * going around and around until something interesting happens.
 211 */
 212int run_guest(struct lg_cpu *cpu, unsigned long __user *user)
 213{
 214        /* We stop running once the Guest is dead. */
 215        while (!cpu->lg->dead) {
 216                unsigned int irq;
 217                bool more;
 218
 219                /* First we run any hypercalls the Guest wants done. */
 220                if (cpu->hcall)
 221                        do_hypercalls(cpu);
 222
 223                /*
 224                 * It's possible the Guest did a NOTIFY hypercall to the
 225                 * Launcher.
 226                 */
 227                if (cpu->pending_notify) {
 228                        /*
 229                         * Does it just needs to write to a registered
 230                         * eventfd (ie. the appropriate virtqueue thread)?
 231                         */
 232                        if (!send_notify_to_eventfd(cpu)) {
 233                                /* OK, we tell the main Launcher. */
 234                                if (put_user(cpu->pending_notify, user))
 235                                        return -EFAULT;
 236                                return sizeof(cpu->pending_notify);
 237                        }
 238                }
 239
 240                /*
 241                 * All long-lived kernel loops need to check with this horrible
 242                 * thing called the freezer.  If the Host is trying to suspend,
 243                 * it stops us.
 244                 */
 245                try_to_freeze();
 246
 247                /* Check for signals */
 248                if (signal_pending(current))
 249                        return -ERESTARTSYS;
 250
 251                /*
 252                 * Check if there are any interrupts which can be delivered now:
 253                 * if so, this sets up the hander to be executed when we next
 254                 * run the Guest.
 255                 */
 256                irq = interrupt_pending(cpu, &more);
 257                if (irq < LGUEST_IRQS)
 258                        try_deliver_interrupt(cpu, irq, more);
 259
 260                /*
 261                 * Just make absolutely sure the Guest is still alive.  One of
 262                 * those hypercalls could have been fatal, for example.
 263                 */
 264                if (cpu->lg->dead)
 265                        break;
 266
 267                /*
 268                 * If the Guest asked to be stopped, we sleep.  The Guest's
 269                 * clock timer will wake us.
 270                 */
 271                if (cpu->halted) {
 272                        set_current_state(TASK_INTERRUPTIBLE);
 273                        /*
 274                         * Just before we sleep, make sure no interrupt snuck in
 275                         * which we should be doing.
 276                         */
 277                        if (interrupt_pending(cpu, &more) < LGUEST_IRQS)
 278                                set_current_state(TASK_RUNNING);
 279                        else
 280                                schedule();
 281                        continue;
 282                }
 283
 284                /*
 285                 * OK, now we're ready to jump into the Guest.  First we put up
 286                 * the "Do Not Disturb" sign:
 287                 */
 288                local_irq_disable();
 289
 290                /* Actually run the Guest until something happens. */
 291                lguest_arch_run_guest(cpu);
 292
 293                /* Now we're ready to be interrupted or moved to other CPUs */
 294                local_irq_enable();
 295
 296                /* Now we deal with whatever happened to the Guest. */
 297                lguest_arch_handle_trap(cpu);
 298        }
 299
 300        /* Special case: Guest is 'dead' but wants a reboot. */
 301        if (cpu->lg->dead == ERR_PTR(-ERESTART))
 302                return -ERESTART;
 303
 304        /* The Guest is dead => "No such file or directory" */
 305        return -ENOENT;
 306}
 307
 308/*H:000
 309 * Welcome to the Host!
 310 *
 311 * By this point your brain has been tickled by the Guest code and numbed by
 312 * the Launcher code; prepare for it to be stretched by the Host code.  This is
 313 * the heart.  Let's begin at the initialization routine for the Host's lg
 314 * module.
 315 */
 316static int __init init(void)
 317{
 318        int err;
 319
 320        /* Lguest can't run under Xen, VMI or itself.  It does Tricky Stuff. */
 321        if (get_kernel_rpl() != 0) {
 322                printk("lguest is afraid of being a guest\n");
 323                return -EPERM;
 324        }
 325
 326        /* First we put the Switcher up in very high virtual memory. */
 327        err = map_switcher();
 328        if (err)
 329                goto out;
 330
 331        /* We might need to reserve an interrupt vector. */
 332        err = init_interrupts();
 333        if (err)
 334                goto unmap;
 335
 336        /* /dev/lguest needs to be registered. */
 337        err = lguest_device_init();
 338        if (err)
 339                goto free_interrupts;
 340
 341        /* Finally we do some architecture-specific setup. */
 342        lguest_arch_host_init();
 343
 344        /* All good! */
 345        return 0;
 346
 347free_interrupts:
 348        free_interrupts();
 349unmap:
 350        unmap_switcher();
 351out:
 352        return err;
 353}
 354
 355/* Cleaning up is just the same code, backwards.  With a little French. */
 356static void __exit fini(void)
 357{
 358        lguest_device_remove();
 359        free_interrupts();
 360        unmap_switcher();
 361
 362        lguest_arch_host_fini();
 363}
 364/*:*/
 365
 366/*
 367 * The Host side of lguest can be a module.  This is a nice way for people to
 368 * play with it.
 369 */
 370module_init(init);
 371module_exit(fini);
 372MODULE_LICENSE("GPL");
 373MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.com.au>");
 374
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