drivers/lguest/hypercalls.c

   1 /*P:500
   2  * Just as userspace programs request kernel operations through a system
   3  * call, the Guest requests Host operations through a "hypercall".  You might
   4  * notice this nomenclature doesn't really follow any logic, but the name has
   5  * been around for long enough that we're stuck with it.  As you'd expect, this
   6  * code is basically a one big switch statement.
   7 :*/
   8
   9 /*  Copyright (C) 2006 Rusty Russell IBM Corporation
  10
  11     This program is free software; you can redistribute it and/or modify
  12     it under the terms of the GNU General Public License as published by
  13     the Free Software Foundation; either version 2 of the License, or
  14     (at your option) any later version.
  15
  16     This program is distributed in the hope that it will be useful,
  17     but WITHOUT ANY WARRANTY; without even the implied warranty of
  18     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  19     GNU General Public License for more details.
  20
  21     You should have received a copy of the GNU General Public License
  22     along with this program; if not, write to the Free Software
  23     Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
  24 */
  25 #include <linux/uaccess.h>
  26 #include <linux/syscalls.h>
  27 #include <linux/mm.h>
  28 #include <linux/ktime.h>
  29 #include <asm/page.h>
  30 #include <asm/pgtable.h>
  31 #include "lg.h"
  32
  33 /*H:120
  34  * This is the core hypercall routine: where the Guest gets what it wants.
  35  * Or gets killed.  Or, in the case of LHCALL_SHUTDOWN, both.
  36  */
  37 static void do_hcall(struct lg_cpu *cpu, struct hcall_args *args)
  38 {
  39         switch (args->arg0) {
  40         case LHCALL_FLUSH_ASYNC:
  41                 /*
  42                  * This call does nothing, except by breaking out of the Guest
  43                  * it makes us process all the asynchronous hypercalls.
  44                  */
  45                 break;
  46         case LHCALL_SEND_INTERRUPTS:
  47                 /*
  48                  * This call does nothing too, but by breaking out of the Guest
  49                  * it makes us process any pending interrupts.
  50                  */
  51                 break;
  52         case LHCALL_LGUEST_INIT:
  53                 /*
  54                  * You can't get here unless you're already initialized.  Don't
  55                  * do that.
  56                  */
  57                 kill_guest(cpu, "already have lguest_data");
  58                 break;
  59         case LHCALL_SHUTDOWN: {
  60                 char msg[128];
  61                 /*
  62                  * Shutdown is such a trivial hypercall that we do it in five
  63                  * lines right here.
  64                  *
  65                  * If the lgread fails, it will call kill_guest() itself; the
  66                  * kill_guest() with the message will be ignored.
  67                  */
  68                 __lgread(cpu, msg, args->arg1, sizeof(msg));
  69                 msg[sizeof(msg)-1] = '\0';
  70                 kill_guest(cpu, "CRASH: %s", msg);
  71                 if (args->arg2 == LGUEST_SHUTDOWN_RESTART)
  72                         cpu->lg->dead = ERR_PTR(-ERESTART);
  73                 break;
  74         }
  75         case LHCALL_FLUSH_TLB:
  76                 /* FLUSH_TLB comes in two flavors, depending on the argument: */
  77                 if (args->arg1)
  78                         guest_pagetable_clear_all(cpu);
  79                 else
  80                         guest_pagetable_flush_user(cpu);
  81                 break;
  82
  83         /*
  84          * All these calls simply pass the arguments through to the right
  85          * routines.
  86          */
  87         case LHCALL_NEW_PGTABLE:
  88                 guest_new_pagetable(cpu, args->arg1);
  89                 break;
  90         case LHCALL_SET_STACK:
  91                 guest_set_stack(cpu, args->arg1, args->arg2, args->arg3);
  92                 break;
  93         case LHCALL_SET_PTE:
  94 #ifdef CONFIG_X86_PAE
  95                 guest_set_pte(cpu, args->arg1, args->arg2,
  96                                 __pte(args->arg3 | (u64)args->arg4 << 32));
  97 #else
  98                 guest_set_pte(cpu, args->arg1, args->arg2, __pte(args->arg3));
  99 #endif
 100                 break;
 101         case LHCALL_SET_PGD:
 102                 guest_set_pgd(cpu->lg, args->arg1, args->arg2);
 103                 break;
 104 #ifdef CONFIG_X86_PAE
 105         case LHCALL_SET_PMD:
 106                 guest_set_pmd(cpu->lg, args->arg1, args->arg2);
 107                 break;
 108 #endif
 109         case LHCALL_SET_CLOCKEVENT:
 110                 guest_set_clockevent(cpu, args->arg1);
 111                 break;
 112         case LHCALL_TS:
 113                 /* This sets the TS flag, as we saw used in run_guest(). */
 114                 cpu->ts = args->arg1;
 115                 break;
 116         case LHCALL_HALT:
 117                 /* Similarly, this sets the halted flag for run_guest(). */
 118                 cpu->halted = 1;
 119                 break;
 120         case LHCALL_NOTIFY:
 121                 cpu->pending_notify = args->arg1;
 122                 break;
 123         default:
 124                 /* It should be an architecture-specific hypercall. */
 125                 if (lguest_arch_do_hcall(cpu, args))
 126                         kill_guest(cpu, "Bad hypercall %li\n", args->arg0);
 127         }
 128 }
 129
 130 /*H:124
 131  * Asynchronous hypercalls are easy: we just look in the array in the
 132  * Guest's "struct lguest_data" to see if any new ones are marked "ready".
 133  *
 134  * We are careful to do these in order: obviously we respect the order the
 135  * Guest put them in the ring, but we also promise the Guest that they will
 136  * happen before any normal hypercall (which is why we check this before
 137  * checking for a normal hcall).
 138  */
 139 static void do_async_hcalls(struct lg_cpu *cpu)
 140 {
 141         unsigned int i;
 142         u8 st[LHCALL_RING_SIZE];
 143
 144         /* For simplicity, we copy the entire call status array in at once. */
 145         if (copy_from_user(&st, &cpu->lg->lguest_data->hcall_status, sizeof(st)))
 146                 return;
 147
 148         /* We process "struct lguest_data"s hcalls[] ring once. */
 149         for (i = 0; i < ARRAY_SIZE(st); i++) {
 150                 struct hcall_args args;
 151                 /*
 152                  * We remember where we were up to from last time.  This makes
 153                  * sure that the hypercalls are done in the order the Guest
 154                  * places them in the ring.
 155                  */
 156                 unsigned int n = cpu->next_hcall;
 157
 158                 /* 0xFF means there's no call here (yet). */
 159                 if (st[n] == 0xFF)
 160                         break;
 161
 162                 /*
 163                  * OK, we have hypercall.  Increment the "next_hcall" cursor,
 164                  * and wrap back to 0 if we reach the end.
 165                  */
 166                 if (++cpu->next_hcall == LHCALL_RING_SIZE)
 167                         cpu->next_hcall = 0;
 168
 169                 /*
 170                  * Copy the hypercall arguments into a local copy of the
 171                  * hcall_args struct.
 172                  */
 173                 if (copy_from_user(&args, &cpu->lg->lguest_data->hcalls[n],
 174                                    sizeof(struct hcall_args))) {
 175                         kill_guest(cpu, "Fetching async hypercalls");
 176                         break;
 177                 }
 178
 179                 /* Do the hypercall, same as a normal one. */
 180                 do_hcall(cpu, &args);
 181
 182                 /* Mark the hypercall done. */
 183                 if (put_user(0xFF, &cpu->lg->lguest_data->hcall_status[n])) {
 184                         kill_guest(cpu, "Writing result for async hypercall");
 185                         break;
 186                 }
 187
 188                 /*
 189                  * Stop doing hypercalls if they want to notify the Launcher:
 190                  * it needs to service this first.
 191                  */
 192                 if (cpu->pending_notify)
 193                         break;
 194         }
 195 }
 196
 197 /*
 198  * Last of all, we look at what happens first of all.  The very first time the
 199  * Guest makes a hypercall, we end up here to set things up:
 200  */
 201 static void initialize(struct lg_cpu *cpu)
 202 {
 203         /*
 204          * You can't do anything until you're initialized.  The Guest knows the
 205          * rules, so we're unforgiving here.
 206          */
 207         if (cpu->hcall->arg0 != LHCALL_LGUEST_INIT) {
 208                 kill_guest(cpu, "hypercall %li before INIT", cpu->hcall->arg0);
 209                 return;
 210         }
 211
 212         if (lguest_arch_init_hypercalls(cpu))
 213                 kill_guest(cpu, "bad guest page %p", cpu->lg->lguest_data);
 214
 215         /*
 216          * The Guest tells us where we're not to deliver interrupts by putting
 217          * the range of addresses into "struct lguest_data".
 218          */
 219         if (get_user(cpu->lg->noirq_start, &cpu->lg->lguest_data->noirq_start)
 220             || get_user(cpu->lg->noirq_end, &cpu->lg->lguest_data->noirq_end))
 221                 kill_guest(cpu, "bad guest page %p", cpu->lg->lguest_data);
 222
 223         /*
 224          * We write the current time into the Guest's data page once so it can
 225          * set its clock.
 226          */
 227         write_timestamp(cpu);
 228
 229         /* page_tables.c will also do some setup. */
 230         page_table_guest_data_init(cpu);
 231
 232         /*
 233          * This is the one case where the above accesses might have been the
 234          * first write to a Guest page.  This may have caused a copy-on-write
 235          * fault, but the old page might be (read-only) in the Guest
 236          * pagetable.
 237          */
 238         guest_pagetable_clear_all(cpu);
 239 }
 240 /*:*/
 241
 242 /*M:013
 243  * If a Guest reads from a page (so creates a mapping) that it has never
 244  * written to, and then the Launcher writes to it (ie. the output of a virtual
 245  * device), the Guest will still see the old page.  In practice, this never
 246  * happens: why would the Guest read a page which it has never written to?  But
 247  * a similar scenario might one day bite us, so it's worth mentioning.
 248  *
 249  * Note that if we used a shared anonymous mapping in the Launcher instead of
 250  * mapping /dev/zero private, we wouldn't worry about cop-on-write.  And we
 251  * need that to switch the Launcher to processes (away from threads) anyway.
 252 :*/
 253
 254 /*H:100
 255  * Hypercalls
 256  *
 257  * Remember from the Guest, hypercalls come in two flavors: normal and
 258  * asynchronous.  This file handles both of types.
 259  */
 260 void do_hypercalls(struct lg_cpu *cpu)
 261 {
 262         /* Not initialized yet?  This hypercall must do it. */
 263         if (unlikely(!cpu->lg->lguest_data)) {
 264                 /* Set up the "struct lguest_data" */
 265                 initialize(cpu);
 266                 /* Hcall is done. */
 267                 cpu->hcall = NULL;
 268                 return;
 269         }
 270
 271         /*
 272          * The Guest has initialized.
 273          *
 274          * Look in the hypercall ring for the async hypercalls:
 275          */
 276         do_async_hcalls(cpu);
 277
 278         /*
 279          * If we stopped reading the hypercall ring because the Guest did a
 280          * NOTIFY to the Launcher, we want to return now.  Otherwise we do
 281          * the hypercall.
 282          */
 283         if (!cpu->pending_notify) {
 284                 do_hcall(cpu, cpu->hcall);
 285                 /*
 286                  * Tricky point: we reset the hcall pointer to mark the
 287                  * hypercall as "done".  We use the hcall pointer rather than
 288                  * the trap number to indicate a hypercall is pending.
 289                  * Normally it doesn't matter: the Guest will run again and
 290                  * update the trap number before we come back here.
 291                  *
 292                  * However, if we are signalled or the Guest sends I/O to the
 293                  * Launcher, the run_guest() loop will exit without running the
 294                  * Guest.  When it comes back it would try to re-run the
 295                  * hypercall.  Finding that bug sucked.
 296                  */
 297                 cpu->hcall = NULL;
 298         }
 299 }
 300
 301 /*
 302  * This routine supplies the Guest with time: it's used for wallclock time at
 303  * initial boot and as a rough time source if the TSC isn't available.
 304  */
 305 void write_timestamp(struct lg_cpu *cpu)
 306 {
 307         struct timespec now;
 308         ktime_get_real_ts(&now);
 309         if (copy_to_user(&cpu->lg->lguest_data->time,
 310                          &now, sizeof(struct timespec)))
 311                 kill_guest(cpu, "Writing timestamp");
 312 }