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_LGUEST_INIT:
  41                 /* You can't get here unless you're already initialized.  Don't
  42                  * do that. */
  43                 kill_guest(cpu, "already have lguest_data");
  44                 break;
  45         case LHCALL_SHUTDOWN: {
  46                 /* Shutdown is such a trivial hypercall that we do it in four
  47                  * lines right here. */
  48                 char msg[128];
  49                 /* If the lgread fails, it will call kill_guest() itself; the
  50                  * kill_guest() with the message will be ignored. */
  51                 __lgread(cpu, msg, args->arg1, sizeof(msg));
  52                 msg[sizeof(msg)-1] = '\0';
  53                 kill_guest(cpu, "CRASH: %s", msg);
  54                 if (args->arg2 == LGUEST_SHUTDOWN_RESTART)
  55                         cpu->lg->dead = ERR_PTR(-ERESTART);
  56                 break;
  57         }
  58         case LHCALL_FLUSH_TLB:
  59                 /* FLUSH_TLB comes in two flavors, depending on the
  60                  * argument: */
  61                 if (args->arg1)
  62                         guest_pagetable_clear_all(cpu);
  63                 else
  64                         guest_pagetable_flush_user(cpu);
  65                 break;
  66
  67         /* All these calls simply pass the arguments through to the right
  68          * routines. */
  69         case LHCALL_NEW_PGTABLE:
  70                 guest_new_pagetable(cpu, args->arg1);
  71                 break;
  72         case LHCALL_SET_STACK:
  73                 guest_set_stack(cpu, args->arg1, args->arg2, args->arg3);
  74                 break;
  75         case LHCALL_SET_PTE:
  76                 guest_set_pte(cpu, args->arg1, args->arg2, __pte(args->arg3));
  77                 break;
  78         case LHCALL_SET_PMD:
  79                 guest_set_pmd(cpu->lg, args->arg1, args->arg2);
  80                 break;
  81         case LHCALL_SET_CLOCKEVENT:
  82                 guest_set_clockevent(cpu, args->arg1);
  83                 break;
  84         case LHCALL_TS:
  85                 /* This sets the TS flag, as we saw used in run_guest(). */
  86                 cpu->ts = args->arg1;
  87                 break;
  88         case LHCALL_HALT:
  89                 /* Similarly, this sets the halted flag for run_guest(). */
  90                 cpu->halted = 1;
  91                 break;
  92         case LHCALL_NOTIFY:
  93                 cpu->pending_notify = args->arg1;
  94                 break;
  95         default:
  96                 /* It should be an architecture-specific hypercall. */
  97                 if (lguest_arch_do_hcall(cpu, args))
  98                         kill_guest(cpu, "Bad hypercall %li\n", args->arg0);
  99         }
 100 }
 101 /*:*/
 102
 103 /*H:124 Asynchronous hypercalls are easy: we just look in the array in the
 104  * Guest's "struct lguest_data" to see if any new ones are marked "ready".
 105  *
 106  * We are careful to do these in order: obviously we respect the order the
 107  * Guest put them in the ring, but we also promise the Guest that they will
 108  * happen before any normal hypercall (which is why we check this before
 109  * checking for a normal hcall). */
 110 static void do_async_hcalls(struct lg_cpu *cpu)
 111 {
 112         unsigned int i;
 113         u8 st[LHCALL_RING_SIZE];
 114
 115         /* For simplicity, we copy the entire call status array in at once. */
 116         if (copy_from_user(&st, &cpu->lg->lguest_data->hcall_status, sizeof(st)))
 117                 return;
 118
 119         /* We process "struct lguest_data"s hcalls[] ring once. */
 120         for (i = 0; i < ARRAY_SIZE(st); i++) {
 121                 struct hcall_args args;
 122                 /* We remember where we were up to from last time.  This makes
 123                  * sure that the hypercalls are done in the order the Guest
 124                  * places them in the ring. */
 125                 unsigned int n = cpu->next_hcall;
 126
 127                 /* 0xFF means there's no call here (yet). */
 128                 if (st[n] == 0xFF)
 129                         break;
 130
 131                 /* OK, we have hypercall.  Increment the "next_hcall" cursor,
 132                  * and wrap back to 0 if we reach the end. */
 133                 if (++cpu->next_hcall == LHCALL_RING_SIZE)
 134                         cpu->next_hcall = 0;
 135
 136                 /* Copy the hypercall arguments into a local copy of
 137                  * the hcall_args struct. */
 138                 if (copy_from_user(&args, &cpu->lg->lguest_data->hcalls[n],
 139                                    sizeof(struct hcall_args))) {
 140                         kill_guest(cpu, "Fetching async hypercalls");
 141                         break;
 142                 }
 143
 144                 /* Do the hypercall, same as a normal one. */
 145                 do_hcall(cpu, &args);
 146
 147                 /* Mark the hypercall done. */
 148                 if (put_user(0xFF, &cpu->lg->lguest_data->hcall_status[n])) {
 149                         kill_guest(cpu, "Writing result for async hypercall");
 150                         break;
 151                 }
 152
 153                 /* Stop doing hypercalls if they want to notify the Launcher:
 154                  * it needs to service this first. */
 155                 if (cpu->pending_notify)
 156                         break;
 157         }
 158 }
 159
 160 /* Last of all, we look at what happens first of all.  The very first time the
 161  * Guest makes a hypercall, we end up here to set things up: */
 162 static void initialize(struct lg_cpu *cpu)
 163 {
 164         /* You can't do anything until you're initialized.  The Guest knows the
 165          * rules, so we're unforgiving here. */
 166         if (cpu->hcall->arg0 != LHCALL_LGUEST_INIT) {
 167                 kill_guest(cpu, "hypercall %li before INIT", cpu->hcall->arg0);
 168                 return;
 169         }
 170
 171         if (lguest_arch_init_hypercalls(cpu))
 172                 kill_guest(cpu, "bad guest page %p", cpu->lg->lguest_data);
 173
 174         /* The Guest tells us where we're not to deliver interrupts by putting
 175          * the range of addresses into "struct lguest_data". */
 176         if (get_user(cpu->lg->noirq_start, &cpu->lg->lguest_data->noirq_start)
 177             || get_user(cpu->lg->noirq_end, &cpu->lg->lguest_data->noirq_end))
 178                 kill_guest(cpu, "bad guest page %p", cpu->lg->lguest_data);
 179
 180         /* We write the current time into the Guest's data page once so it can
 181          * set its clock. */
 182         write_timestamp(cpu);
 183
 184         /* page_tables.c will also do some setup. */
 185         page_table_guest_data_init(cpu);
 186
 187         /* This is the one case where the above accesses might have been the
 188          * first write to a Guest page.  This may have caused a copy-on-write
 189          * fault, but the old page might be (read-only) in the Guest
 190          * pagetable. */
 191         guest_pagetable_clear_all(cpu);
 192 }
 193 /*:*/
 194
 195 /*M:013 If a Guest reads from a page (so creates a mapping) that it has never
 196  * written to, and then the Launcher writes to it (ie. the output of a virtual
 197  * device), the Guest will still see the old page.  In practice, this never
 198  * happens: why would the Guest read a page which it has never written to?  But
 199  * a similar scenario might one day bite us, so it's worth mentioning. :*/
 200
 201 /*H:100
 202  * Hypercalls
 203  *
 204  * Remember from the Guest, hypercalls come in two flavors: normal and
 205  * asynchronous.  This file handles both of types.
 206  */
 207 void do_hypercalls(struct lg_cpu *cpu)
 208 {
 209         /* Not initialized yet?  This hypercall must do it. */
 210         if (unlikely(!cpu->lg->lguest_data)) {
 211                 /* Set up the "struct lguest_data" */
 212                 initialize(cpu);
 213                 /* Hcall is done. */
 214                 cpu->hcall = NULL;
 215                 return;
 216         }
 217
 218         /* The Guest has initialized.
 219          *
 220          * Look in the hypercall ring for the async hypercalls: */
 221         do_async_hcalls(cpu);
 222
 223         /* If we stopped reading the hypercall ring because the Guest did a
 224          * NOTIFY to the Launcher, we want to return now.  Otherwise we do
 225          * the hypercall. */
 226         if (!cpu->pending_notify) {
 227                 do_hcall(cpu, cpu->hcall);
 228                 /* Tricky point: we reset the hcall pointer to mark the
 229                  * hypercall as "done".  We use the hcall pointer rather than
 230                  * the trap number to indicate a hypercall is pending.
 231                  * Normally it doesn't matter: the Guest will run again and
 232                  * update the trap number before we come back here.
 233                  *
 234                  * However, if we are signalled or the Guest sends I/O to the
 235                  * Launcher, the run_guest() loop will exit without running the
 236                  * Guest.  When it comes back it would try to re-run the
 237                  * hypercall.  Finding that bug sucked. */
 238                 cpu->hcall = NULL;
 239         }
 240 }
 241
 242 /* This routine supplies the Guest with time: it's used for wallclock time at
 243  * initial boot and as a rough time source if the TSC isn't available. */
 244 void write_timestamp(struct lg_cpu *cpu)
 245 {
 246         struct timespec now;
 247         ktime_get_real_ts(&now);
 248         if (copy_to_user(&cpu->lg->lguest_data->time,
 249                          &now, sizeof(struct timespec)))
 250                 kill_guest(cpu, "Writing timestamp");
 251 }