drivers/lguest/hypercalls.c

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