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
  23
  24static struct vm_struct *switcher_vma;
  25static struct page **switcher_page;
  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        /*
  56         * We allocate an array of struct page pointers.  map_vm_area() wants
  57         * this, rather than just an array of pages.
  58         */
  59        switcher_page = kmalloc(sizeof(switcher_page[0])*TOTAL_SWITCHER_PAGES,
  60                                GFP_KERNEL);
  61        if (!switcher_page) {
  62                err = -ENOMEM;
  63                goto out;
  64        }
  65
  66        /*
  67         * Now we actually allocate the pages.  The Guest will see these pages,
  68         * so we make sure they're zeroed.
  69         */
  70        for (i = 0; i < TOTAL_SWITCHER_PAGES; i++) {
  71                switcher_page[i] = alloc_page(GFP_KERNEL|__GFP_ZERO);
  72                if (!switcher_page[i]) {
  73                        err = -ENOMEM;
  74                        goto free_some_pages;
  75                }
  76        }
  77
  78        /*
  79         * First we check that the Switcher won't overlap the fixmap area at
  80         * the top of memory.  It's currently nowhere near, but it could have
  81         * very strange effects if it ever happened.
  82         */
  83        if (SWITCHER_ADDR + (TOTAL_SWITCHER_PAGES+1)*PAGE_SIZE > FIXADDR_START){
  84                err = -ENOMEM;
  85                printk("lguest: mapping switcher would thwack fixmap\n");
  86                goto free_pages;
  87        }
  88
  89        /*
  90         * Now we reserve the "virtual memory area" we want: 0xFFC00000
  91         * (SWITCHER_ADDR).  We might not get it in theory, but in practice
  92         * it's worked so far.  The end address needs +1 because __get_vm_area
  93         * allocates an extra guard page, so we need space for that.
  94         */
  95        switcher_vma = __get_vm_area(TOTAL_SWITCHER_PAGES * PAGE_SIZE,
  96                                     VM_ALLOC, SWITCHER_ADDR, SWITCHER_ADDR
  97                                     + (TOTAL_SWITCHER_PAGES+1) * PAGE_SIZE);
  98        if (!switcher_vma) {
  99                err = -ENOMEM;
 100                printk("lguest: could not map switcher pages high\n");
 101                goto free_pages;
 102        }
 103
 104        /*
 105         * This code actually sets up the pages we've allocated to appear at
 106         * SWITCHER_ADDR.  map_vm_area() takes the vma we allocated above, the
 107         * kind of pages we're mapping (kernel pages), and a pointer to our
 108         * array of struct pages.  It increments that pointer, but we don't
 109         * care.
 110         */
 111        pagep = switcher_page;
 112        err = map_vm_area(switcher_vma, PAGE_KERNEL_EXEC, &pagep);
 113        if (err) {
 114                printk("lguest: map_vm_area failed: %i\n", err);
 115                goto free_vma;
 116        }
 117
 118        /*
 119         * Now the Switcher is mapped at the right address, we can't fail!
 120         * Copy in the compiled-in Switcher code (from x86/switcher_32.S).
 121         */
 122        memcpy(switcher_vma->addr, start_switcher_text,
 123               end_switcher_text - start_switcher_text);
 124
 125        printk(KERN_INFO "lguest: mapped switcher at %p\n",
 126               switcher_vma->addr);
 127        /* And we succeeded... */
 128        return 0;
 129
 130free_vma:
 131        vunmap(switcher_vma->addr);
 132free_pages:
 133        i = TOTAL_SWITCHER_PAGES;
 134free_some_pages:
 135        for (--i; i >= 0; i--)
 136                __free_pages(switcher_page[i], 0);
 137        kfree(switcher_page);
 138out:
 139        return err;
 140}
 141/*:*/
 142
 143/* Cleaning up the mapping when the module is unloaded is almost... too easy. */
 144static void unmap_switcher(void)
 145{
 146        unsigned int i;
 147
 148        /* vunmap() undoes *both* map_vm_area() and __get_vm_area(). */
 149        vunmap(switcher_vma->addr);
 150        /* Now we just need to free the pages we copied the switcher into */
 151        for (i = 0; i < TOTAL_SWITCHER_PAGES; i++)
 152                __free_pages(switcher_page[i], 0);
 153        kfree(switcher_page);
 154}
 155
 156/*H:032
 157 * Dealing With Guest Memory.
 158 *
 159 * Before we go too much further into the Host, we need to grok the routines
 160 * we use to deal with Guest memory.
 161 *
 162 * When the Guest gives us (what it thinks is) a physical address, we can use
 163 * the normal copy_from_user() & copy_to_user() on the corresponding place in
 164 * the memory region allocated by the Launcher.
 165 *
 166 * But we can't trust the Guest: it might be trying to access the Launcher
 167 * code.  We have to check that the range is below the pfn_limit the Launcher
 168 * gave us.  We have to make sure that addr + len doesn't give us a false
 169 * positive by overflowing, too.
 170 */
 171bool lguest_address_ok(const struct lguest *lg,
 172                       unsigned long addr, unsigned long len)
 173{
 174        return (addr+len) / PAGE_SIZE < lg->pfn_limit && (addr+len >= addr);
 175}
 176
 177/*
 178 * This routine copies memory from the Guest.  Here we can see how useful the
 179 * kill_lguest() routine we met in the Launcher can be: we return a random
 180 * value (all zeroes) instead of needing to return an error.
 181 */
 182void __lgread(struct lg_cpu *cpu, void *b, unsigned long addr, unsigned bytes)
 183{
 184        if (!lguest_address_ok(cpu->lg, addr, bytes)
 185            || copy_from_user(b, cpu->lg->mem_base + addr, bytes) != 0) {
 186                /* copy_from_user should do this, but as we rely on it... */
 187                memset(b, 0, bytes);
 188                kill_guest(cpu, "bad read address %#lx len %u", addr, bytes);
 189        }
 190}
 191
 192/* This is the write (copy into Guest) version. */
 193void __lgwrite(struct lg_cpu *cpu, unsigned long addr, const void *b,
 194               unsigned bytes)
 195{
 196        if (!lguest_address_ok(cpu->lg, addr, bytes)
 197            || copy_to_user(cpu->lg->mem_base + addr, b, bytes) != 0)
 198                kill_guest(cpu, "bad write address %#lx len %u", addr, bytes);
 199}
 200/*:*/
 201
 202/*H:030
 203 * Let's jump straight to the the main loop which runs the Guest.
 204 * Remember, this is called by the Launcher reading /dev/lguest, and we keep
 205 * going around and around until something interesting happens.
 206 */
 207int run_guest(struct lg_cpu *cpu, unsigned long __user *user)
 208{
 209        /* We stop running once the Guest is dead. */
 210        while (!cpu->lg->dead) {
 211                unsigned int irq;
 212                bool more;
 213
 214                /* First we run any hypercalls the Guest wants done. */
 215                if (cpu->hcall)
 216                        do_hypercalls(cpu);
 217
 218                /*
 219                 * It's possible the Guest did a NOTIFY hypercall to the
 220                 * Launcher.
 221                 */
 222                if (cpu->pending_notify) {
 223                        /*
 224                         * Does it just needs to write to a registered
 225                         * eventfd (ie. the appropriate virtqueue thread)?
 226                         */
 227                        if (!send_notify_to_eventfd(cpu)) {
 228                                /* OK, we tell the main Launcher. */
 229                                if (put_user(cpu->pending_notify, user))
 230                                        return -EFAULT;
 231                                return sizeof(cpu->pending_notify);
 232                        }
 233                }
 234
 235                /*
 236                 * All long-lived kernel loops need to check with this horrible
 237                 * thing called the freezer.  If the Host is trying to suspend,
 238                 * it stops us.
 239                 */
 240                try_to_freeze();
 241
 242                /* Check for signals */
 243                if (signal_pending(current))
 244                        return -ERESTARTSYS;
 245
 246                /*
 247                 * Check if there are any interrupts which can be delivered now:
 248                 * if so, this sets up the hander to be executed when we next
 249                 * run the Guest.
 250                 */
 251                irq = interrupt_pending(cpu, &more);
 252                if (irq < LGUEST_IRQS)
 253                        try_deliver_interrupt(cpu, irq, more);
 254
 255                /*
 256                 * Just make absolutely sure the Guest is still alive.  One of
 257                 * those hypercalls could have been fatal, for example.
 258                 */
 259                if (cpu->lg->dead)
 260                        break;
 261
 262                /*
 263                 * If the Guest asked to be stopped, we sleep.  The Guest's
 264                 * clock timer will wake us.
 265                 */
 266                if (cpu->halted) {
 267                        set_current_state(TASK_INTERRUPTIBLE);
 268                        /*
 269                         * Just before we sleep, make sure no interrupt snuck in
 270                         * which we should be doing.
 271                         */
 272                        if (interrupt_pending(cpu, &more) < LGUEST_IRQS)
 273                                set_current_state(TASK_RUNNING);
 274                        else
 275                                schedule();
 276                        continue;
 277                }
 278
 279                /*
 280                 * OK, now we're ready to jump into the Guest.  First we put up
 281                 * the "Do Not Disturb" sign:
 282                 */
 283                local_irq_disable();
 284
 285                /* Actually run the Guest until something happens. */
 286                lguest_arch_run_guest(cpu);
 287
 288                /* Now we're ready to be interrupted or moved to other CPUs */
 289                local_irq_enable();
 290
 291                /* Now we deal with whatever happened to the Guest. */
 292                lguest_arch_handle_trap(cpu);
 293        }
 294
 295        /* Special case: Guest is 'dead' but wants a reboot. */
 296        if (cpu->lg->dead == ERR_PTR(-ERESTART))
 297                return -ERESTART;
 298
 299        /* The Guest is dead => "No such file or directory" */
 300        return -ENOENT;
 301}
 302
 303/*H:000
 304 * Welcome to the Host!
 305 *
 306 * By this point your brain has been tickled by the Guest code and numbed by
 307 * the Launcher code; prepare for it to be stretched by the Host code.  This is
 308 * the heart.  Let's begin at the initialization routine for the Host's lg
 309 * module.
 310 */
 311static int __init init(void)
 312{
 313        int err;
 314
 315        /* Lguest can't run under Xen, VMI or itself.  It does Tricky Stuff. */
 316        if (get_kernel_rpl() != 0) {
 317                printk("lguest is afraid of being a guest\n");
 318                return -EPERM;
 319        }
 320
 321        /* First we put the Switcher up in very high virtual memory. */
 322        err = map_switcher();
 323        if (err)
 324                goto out;
 325
 326        /* Now we set up the pagetable implementation for the Guests. */
 327        err = init_pagetables(switcher_page, SHARED_SWITCHER_PAGES);
 328        if (err)
 329                goto unmap;
 330
 331        /* We might need to reserve an interrupt vector. */
 332        err = init_interrupts();
 333        if (err)
 334                goto free_pgtables;
 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();
 349free_pgtables:
 350        free_pagetables();
 351unmap:
 352        unmap_switcher();
 353out:
 354        return err;
 355}
 356
 357/* Cleaning up is just the same code, backwards.  With a little French. */
 358static void __exit fini(void)
 359{
 360        lguest_device_remove();
 361        free_interrupts();
 362        free_pagetables();
 363        unmap_switcher();
 364
 365        lguest_arch_host_fini();
 366}
 367/*:*/
 368
 369/*
 370 * The Host side of lguest can be a module.  This is a nice way for people to
 371 * play with it.
 372 */
 373module_init(init);
 374module_exit(fini);
 375MODULE_LICENSE("GPL");
 376MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.com.au>");
 377
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