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         default:
 121                 /* It should be an architecture-specific hypercall. */
 122                 if (lguest_arch_do_hcall(cpu, args))
 123                         kill_guest(cpu, "Bad hypercall %li\n", args->arg0);
 124         }
 125 }
 126
 127 /*H:124
 128  * Asynchronous hypercalls are easy: we just look in the array in the
 129  * Guest's "struct lguest_data" to see if any new ones are marked "ready".
 130  *
 131  * We are careful to do these in order: obviously we respect the order the
 132  * Guest put them in the ring, but we also promise the Guest that they will
 133  * happen before any normal hypercall (which is why we check this before
 134  * checking for a normal hcall).
 135  */
 136 static void do_async_hcalls(struct lg_cpu *cpu)
 137 {
 138         unsigned int i;
 139         u8 st[LHCALL_RING_SIZE];
 140
 141         /* For simplicity, we copy the entire call status array in at once. */
 142         if (copy_from_user(&st, &cpu->lg->lguest_data->hcall_status, sizeof(st)))
 143                 return;
 144
 145         /* We process "struct lguest_data"s hcalls[] ring once. */
 146         for (i = 0; i < ARRAY_SIZE(st); i++) {
 147                 struct hcall_args args;
 148                 /*
 149                  * We remember where we were up to from last time.  This makes
 150                  * sure that the hypercalls are done in the order the Guest
 151                  * places them in the ring.
 152                  */
 153                 unsigned int n = cpu->next_hcall;
 154
 155                 /* 0xFF means there's no call here (yet). */
 156                 if (st[n] == 0xFF)
 157                         break;
 158
 159                 /*
 160                  * OK, we have hypercall.  Increment the "next_hcall" cursor,
 161                  * and wrap back to 0 if we reach the end.
 162                  */
 163                 if (++cpu->next_hcall == LHCALL_RING_SIZE)
 164                         cpu->next_hcall = 0;
 165
 166                 /*
 167                  * Copy the hypercall arguments into a local copy of the
 168                  * hcall_args struct.
 169                  */
 170                 if (copy_from_user(&args, &cpu->lg->lguest_data->hcalls[n],
 171                                    sizeof(struct hcall_args))) {
 172                         kill_guest(cpu, "Fetching async hypercalls");
 173                         break;
 174                 }
 175
 176                 /* Do the hypercall, same as a normal one. */
 177                 do_hcall(cpu, &args);
 178
 179                 /* Mark the hypercall done. */
 180                 if (put_user(0xFF, &cpu->lg->lguest_data->hcall_status[n])) {
 181                         kill_guest(cpu, "Writing result for async hypercall");
 182                         break;
 183                 }
 184
 185                 /*
 186                  * Stop doing hypercalls if they want to notify the Launcher:
 187                  * it needs to service this first.
 188                  */
 189                 if (cpu->pending.trap)
 190                         break;
 191         }
 192 }
 193
 194 /*
 195  * Last of all, we look at what happens first of all.  The very first time the
 196  * Guest makes a hypercall, we end up here to set things up:
 197  */
 198 static void initialize(struct lg_cpu *cpu)
 199 {
 200         /*
 201          * You can't do anything until you're initialized.  The Guest knows the
 202          * rules, so we're unforgiving here.
 203          */
 204         if (cpu->hcall->arg0 != LHCALL_LGUEST_INIT) {
 205                 kill_guest(cpu, "hypercall %li before INIT", cpu->hcall->arg0);
 206                 return;
 207         }
 208
 209         if (lguest_arch_init_hypercalls(cpu))
 210                 kill_guest(cpu, "bad guest page %p", cpu->lg->lguest_data);
 211
 212         /*
 213          * The Guest tells us where we're not to deliver interrupts by putting
 214          * the instruction address into "struct lguest_data".
 215          */
 216         if (get_user(cpu->lg->noirq_iret, &cpu->lg->lguest_data->noirq_iret))
 217                 kill_guest(cpu, "bad guest page %p", cpu->lg->lguest_data);
 218
 219         /*
 220          * We write the current time into the Guest's data page once so it can
 221          * set its clock.
 222          */
 223         write_timestamp(cpu);
 224
 225         /* page_tables.c will also do some setup. */
 226         page_table_guest_data_init(cpu);
 227
 228         /*
 229          * This is the one case where the above accesses might have been the
 230          * first write to a Guest page.  This may have caused a copy-on-write
 231          * fault, but the old page might be (read-only) in the Guest
 232          * pagetable.
 233          */
 234         guest_pagetable_clear_all(cpu);
 235 }
 236 /*:*/
 237
 238 /*M:013
 239  * If a Guest reads from a page (so creates a mapping) that it has never
 240  * written to, and then the Launcher writes to it (ie. the output of a virtual
 241  * device), the Guest will still see the old page.  In practice, this never
 242  * happens: why would the Guest read a page which it has never written to?  But
 243  * a similar scenario might one day bite us, so it's worth mentioning.
 244  *
 245  * Note that if we used a shared anonymous mapping in the Launcher instead of
 246  * mapping /dev/zero private, we wouldn't worry about cop-on-write.  And we
 247  * need that to switch the Launcher to processes (away from threads) anyway.
 248 :*/
 249
 250 /*H:100
 251  * Hypercalls
 252  *
 253  * Remember from the Guest, hypercalls come in two flavors: normal and
 254  * asynchronous.  This file handles both of types.
 255  */
 256 void do_hypercalls(struct lg_cpu *cpu)
 257 {
 258         /* Not initialized yet?  This hypercall must do it. */
 259         if (unlikely(!cpu->lg->lguest_data)) {
 260                 /* Set up the "struct lguest_data" */
 261                 initialize(cpu);
 262                 /* Hcall is done. */
 263                 cpu->hcall = NULL;
 264                 return;
 265         }
 266
 267         /*
 268          * The Guest has initialized.
 269          *
 270          * Look in the hypercall ring for the async hypercalls:
 271          */
 272         do_async_hcalls(cpu);
 273
 274         /*
 275          * If we stopped reading the hypercall ring because the Guest did a
 276          * NOTIFY to the Launcher, we want to return now.  Otherwise we do
 277          * the hypercall.
 278          */
 279         if (!cpu->pending.trap) {
 280                 do_hcall(cpu, cpu->hcall);
 281                 /*
 282                  * Tricky point: we reset the hcall pointer to mark the
 283                  * hypercall as "done".  We use the hcall pointer rather than
 284                  * the trap number to indicate a hypercall is pending.
 285                  * Normally it doesn't matter: the Guest will run again and
 286                  * update the trap number before we come back here.
 287                  *
 288                  * However, if we are signalled or the Guest sends I/O to the
 289                  * Launcher, the run_guest() loop will exit without running the
 290                  * Guest.  When it comes back it would try to re-run the
 291                  * hypercall.  Finding that bug sucked.
 292                  */
 293                 cpu->hcall = NULL;
 294         }
 295 }
 296
 297 /*
 298  * This routine supplies the Guest with time: it's used for wallclock time at
 299  * initial boot and as a rough time source if the TSC isn't available.
 300  */
 301 void write_timestamp(struct lg_cpu *cpu)
 302 {
 303         struct timespec now;
 304         ktime_get_real_ts(&now);
 305         if (copy_to_user(&cpu->lg->lguest_data->time,
 306                          &now, sizeof(struct timespec)))
 307                 kill_guest(cpu, "Writing timestamp");
 308 }