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 <linux/ktime.h>
  27 #include <asm/page.h>
  28 #include <asm/pgtable.h>
  29 #include "lg.h"
  30
  31 /*H:120 This is the core hypercall routine: where the Guest gets what it wants.
  32  * Or gets killed.  Or, in the case of LHCALL_SHUTDOWN, both. */
  33 static void do_hcall(struct lg_cpu *cpu, struct hcall_args *args)
  34 {
  35         switch (args->arg0) {
  36         case LHCALL_FLUSH_ASYNC:
  37                 /* This call does nothing, except by breaking out of the Guest
  38                  * it makes us process all the asynchronous hypercalls. */
  39                 break;
  40         case LHCALL_SEND_INTERRUPTS:
  41                 /* This call does nothing too, but by breaking out of the Guest
  42                  * it makes us process any pending interrupts. */
  43                 break;
  44         case LHCALL_LGUEST_INIT:
  45                 /* You can't get here unless you're already initialized.  Don't
  46                  * do that. */
  47                 kill_guest(cpu, "already have lguest_data");
  48                 break;
  49         case LHCALL_SHUTDOWN: {
  50                 /* Shutdown is such a trivial hypercall that we do it in four
  51                  * lines right here. */
  52                 char msg[128];
  53                 /* If the lgread fails, it will call kill_guest() itself; the
  54                  * kill_guest() with the message will be ignored. */
  55                 __lgread(cpu, msg, args->arg1, sizeof(msg));
  56                 msg[sizeof(msg)-1] = '\0';
  57                 kill_guest(cpu, "CRASH: %s", msg);
  58                 if (args->arg2 == LGUEST_SHUTDOWN_RESTART)
  59                         cpu->lg->dead = ERR_PTR(-ERESTART);
  60                 break;
  61         }
  62         case LHCALL_FLUSH_TLB:
  63                 /* FLUSH_TLB comes in two flavors, depending on the
  64                  * argument: */
  65                 if (args->arg1)
  66                         guest_pagetable_clear_all(cpu);
  67                 else
  68                         guest_pagetable_flush_user(cpu);
  69                 break;
  70
  71         /* All these calls simply pass the arguments through to the right
  72          * routines. */
  73         case LHCALL_NEW_PGTABLE:
  74                 guest_new_pagetable(cpu, args->arg1);
  75                 break;
  76         case LHCALL_SET_STACK:
  77                 guest_set_stack(cpu, args->arg1, args->arg2, args->arg3);
  78                 break;
  79         case LHCALL_SET_PTE:
  80 #ifdef CONFIG_X86_PAE
  81                 guest_set_pte(cpu, args->arg1, args->arg2,
  82                                 __pte(args->arg3 | (u64)args->arg4 << 32));
  83 #else
  84                 guest_set_pte(cpu, args->arg1, args->arg2, __pte(args->arg3));
  85 #endif
  86                 break;
  87         case LHCALL_SET_PGD:
  88                 guest_set_pgd(cpu->lg, args->arg1, args->arg2);
  89                 break;
  90 #ifdef CONFIG_X86_PAE
  91         case LHCALL_SET_PMD:
  92                 guest_set_pmd(cpu->lg, args->arg1, args->arg2);
  93                 break;
  94 #endif
  95         case LHCALL_SET_CLOCKEVENT:
  96                 guest_set_clockevent(cpu, args->arg1);
  97                 break;
  98         case LHCALL_TS:
  99                 /* This sets the TS flag, as we saw used in run_guest(). */
 100                 cpu->ts = args->arg1;
 101                 break;
 102         case LHCALL_HALT:
 103                 /* Similarly, this sets the halted flag for run_guest(). */
 104                 cpu->halted = 1;
 105                 break;
 106         case LHCALL_NOTIFY:
 107                 cpu->pending_notify = args->arg1;
 108                 break;
 109         default:
 110                 /* It should be an architecture-specific hypercall. */
 111                 if (lguest_arch_do_hcall(cpu, args))
 112                         kill_guest(cpu, "Bad hypercall %li\n", args->arg0);
 113         }
 114 }
 115 /*:*/
 116
 117 /*H:124 Asynchronous hypercalls are easy: we just look in the array in the
 118  * Guest's "struct lguest_data" to see if any new ones are marked "ready".
 119  *
 120  * We are careful to do these in order: obviously we respect the order the
 121  * Guest put them in the ring, but we also promise the Guest that they will
 122  * happen before any normal hypercall (which is why we check this before
 123  * checking for a normal hcall). */
 124 static void do_async_hcalls(struct lg_cpu *cpu)
 125 {
 126         unsigned int i;
 127         u8 st[LHCALL_RING_SIZE];
 128
 129         /* For simplicity, we copy the entire call status array in at once. */
 130         if (copy_from_user(&st, &cpu->lg->lguest_data->hcall_status, sizeof(st)))
 131                 return;
 132
 133         /* We process "struct lguest_data"s hcalls[] ring once. */
 134         for (i = 0; i < ARRAY_SIZE(st); i++) {
 135                 struct hcall_args args;
 136                 /* We remember where we were up to from last time.  This makes
 137                  * sure that the hypercalls are done in the order the Guest
 138                  * places them in the ring. */
 139                 unsigned int n = cpu->next_hcall;
 140
 141                 /* 0xFF means there's no call here (yet). */
 142                 if (st[n] == 0xFF)
 143                         break;
 144
 145                 /* OK, we have hypercall.  Increment the "next_hcall" cursor,
 146                  * and wrap back to 0 if we reach the end. */
 147                 if (++cpu->next_hcall == LHCALL_RING_SIZE)
 148                         cpu->next_hcall = 0;
 149
 150                 /* Copy the hypercall arguments into a local copy of
 151                  * the hcall_args struct. */
 152                 if (copy_from_user(&args, &cpu->lg->lguest_data->hcalls[n],
 153                                    sizeof(struct hcall_args))) {
 154                         kill_guest(cpu, "Fetching async hypercalls");
 155                         break;
 156                 }
 157
 158                 /* Do the hypercall, same as a normal one. */
 159                 do_hcall(cpu, &args);
 160
 161                 /* Mark the hypercall done. */
 162                 if (put_user(0xFF, &cpu->lg->lguest_data->hcall_status[n])) {
 163                         kill_guest(cpu, "Writing result for async hypercall");
 164                         break;
 165                 }
 166
 167                 /* Stop doing hypercalls if they want to notify the Launcher:
 168                  * it needs to service this first. */
 169                 if (cpu->pending_notify)
 170                         break;
 171         }
 172 }
 173
 174 /* Last of all, we look at what happens first of all.  The very first time the
 175  * Guest makes a hypercall, we end up here to set things up: */
 176 static void initialize(struct lg_cpu *cpu)
 177 {
 178         /* You can't do anything until you're initialized.  The Guest knows the
 179          * rules, so we're unforgiving here. */
 180         if (cpu->hcall->arg0 != LHCALL_LGUEST_INIT) {
 181                 kill_guest(cpu, "hypercall %li before INIT", cpu->hcall->arg0);
 182                 return;
 183         }
 184
 185         if (lguest_arch_init_hypercalls(cpu))
 186                 kill_guest(cpu, "bad guest page %p", cpu->lg->lguest_data);
 187
 188         /* The Guest tells us where we're not to deliver interrupts by putting
 189          * the range of addresses into "struct lguest_data". */
 190         if (get_user(cpu->lg->noirq_start, &cpu->lg->lguest_data->noirq_start)
 191             || get_user(cpu->lg->noirq_end, &cpu->lg->lguest_data->noirq_end))
 192                 kill_guest(cpu, "bad guest page %p", cpu->lg->lguest_data);
 193
 194         /* We write the current time into the Guest's data page once so it can
 195          * set its clock. */
 196         write_timestamp(cpu);
 197
 198         /* page_tables.c will also do some setup. */
 199         page_table_guest_data_init(cpu);
 200
 201         /* This is the one case where the above accesses might have been the
 202          * first write to a Guest page.  This may have caused a copy-on-write
 203          * fault, but the old page might be (read-only) in the Guest
 204          * pagetable. */
 205         guest_pagetable_clear_all(cpu);
 206 }
 207 /*:*/
 208
 209 /*M:013 If a Guest reads from a page (so creates a mapping) that it has never
 210  * written to, and then the Launcher writes to it (ie. the output of a virtual
 211  * device), the Guest will still see the old page.  In practice, this never
 212  * happens: why would the Guest read a page which it has never written to?  But
 213  * a similar scenario might one day bite us, so it's worth mentioning. :*/
 214
 215 /*H:100
 216  * Hypercalls
 217  *
 218  * Remember from the Guest, hypercalls come in two flavors: normal and
 219  * asynchronous.  This file handles both of types.
 220  */
 221 void do_hypercalls(struct lg_cpu *cpu)
 222 {
 223         /* Not initialized yet?  This hypercall must do it. */
 224         if (unlikely(!cpu->lg->lguest_data)) {
 225                 /* Set up the "struct lguest_data" */
 226                 initialize(cpu);
 227                 /* Hcall is done. */
 228                 cpu->hcall = NULL;
 229                 return;
 230         }
 231
 232         /* The Guest has initialized.
 233          *
 234          * Look in the hypercall ring for the async hypercalls: */
 235         do_async_hcalls(cpu);
 236
 237         /* If we stopped reading the hypercall ring because the Guest did a
 238          * NOTIFY to the Launcher, we want to return now.  Otherwise we do
 239          * the hypercall. */
 240         if (!cpu->pending_notify) {
 241                 do_hcall(cpu, cpu->hcall);
 242                 /* Tricky point: we reset the hcall pointer to mark the
 243                  * hypercall as "done".  We use the hcall pointer rather than
 244                  * the trap number to indicate a hypercall is pending.
 245                  * Normally it doesn't matter: the Guest will run again and
 246                  * update the trap number before we come back here.
 247                  *
 248                  * However, if we are signalled or the Guest sends I/O to the
 249                  * Launcher, the run_guest() loop will exit without running the
 250                  * Guest.  When it comes back it would try to re-run the
 251                  * hypercall.  Finding that bug sucked. */
 252                 cpu->hcall = NULL;
 253         }
 254 }
 255
 256 /* This routine supplies the Guest with time: it's used for wallclock time at
 257  * initial boot and as a rough time source if the TSC isn't available. */
 258 void write_timestamp(struct lg_cpu *cpu)
 259 {
 260         struct timespec now;
 261         ktime_get_real_ts(&now);
 262         if (copy_to_user(&cpu->lg->lguest_data->time,
 263                          &now, sizeof(struct timespec)))
 264                 kill_guest(cpu, "Writing timestamp");
 265 }