linux/drivers/lguest/hypercalls.c

/*P:500 Just as userspace programs request kernel operations through a system
 * call, the Guest requests Host operations through a "hypercall".  You might
 * notice this nomenclature doesn't really follow any logic, but the name has
 * been around for long enough that we're stuck with it.  As you'd expect, this
 * code is basically a one big switch statement. :*/

/*  Copyright (C) 2006 Rusty Russell IBM Corporation

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
*/
#include <linux/uaccess.h>
#include <linux/syscalls.h>
#include <linux/mm.h>
#include <asm/page.h>
#include <asm/pgtable.h>
#include "lg.h"

/*H:120 This is the core hypercall routine: where the Guest gets what it wants.
 * Or gets killed.  Or, in the case of LHCALL_CRASH, both. */
static void do_hcall(struct lguest *lg, struct hcall_args *args)
{
	switch (args->arg0) {
	case LHCALL_FLUSH_ASYNC:
		/* This call does nothing, except by breaking out of the Guest
		 * it makes us process all the asynchronous hypercalls. */
		break;
	case LHCALL_LGUEST_INIT:
		/* You can't get here unless you're already initialized.  Don't
		 * do that. */
		kill_guest(lg, "already have lguest_data");
		break;
	case LHCALL_CRASH: {
		/* Crash is such a trivial hypercall that we do it in four
		 * lines right here. */
		char msg[128];
		/* If the lgread fails, it will call kill_guest() itself; the
		 * kill_guest() with the message will be ignored. */
		lgread(lg, msg, args->arg1, sizeof(msg));
		msg[sizeof(msg)-1] = '\0';
		kill_guest(lg, "CRASH: %s", msg);
		break;
	}
	case LHCALL_FLUSH_TLB:
		/* FLUSH_TLB comes in two flavors, depending on the
		 * argument: */
		if (args->arg1)
			guest_pagetable_clear_all(lg);
		else
			guest_pagetable_flush_user(lg);
		break;
	case LHCALL_BIND_DMA:
		/* BIND_DMA really wants four arguments, but it's the only call
		 * which does.  So the Guest packs the number of buffers and
		 * the interrupt number into the final argument, and we decode
		 * it here.  This can legitimately fail, since we currently
		 * place a limit on the number of DMA pools a Guest can have.
		 * So we return true or false from this call. */
		args->arg0 = bind_dma(lg, args->arg1, args->arg2,
				     args->arg3 >> 8, args->arg3 & 0xFF);
		break;

	/* All these calls simply pass the arguments through to the right
	 * routines. */
	case LHCALL_SEND_DMA:
		send_dma(lg, args->arg1, args->arg2);
		break;
	case LHCALL_NEW_PGTABLE:
		guest_new_pagetable(lg, args->arg1);
		break;
	case LHCALL_SET_STACK:
		guest_set_stack(lg, args->arg1, args->arg2, args->arg3);
		break;
	case LHCALL_SET_PTE:
		guest_set_pte(lg, args->arg1, args->arg2, __pte(args->arg3));
		break;
	case LHCALL_SET_PMD:
		guest_set_pmd(lg, args->arg1, args->arg2);
		break;
	case LHCALL_SET_CLOCKEVENT:
		guest_set_clockevent(lg, args->arg1);
		break;
	case LHCALL_TS:
		/* This sets the TS flag, as we saw used in run_guest(). */
		lg->ts = args->arg1;
		break;
	case LHCALL_HALT:
		/* Similarly, this sets the halted flag for run_guest(). */
		lg->halted = 1;
		break;
	default:
		if (lguest_arch_do_hcall(lg, args))
			kill_guest(lg, "Bad hypercall %li\n", args->arg0);
	}
}
/*:*/

/*H:124 Asynchronous hypercalls are easy: we just look in the array in the
 * Guest's "struct lguest_data" to see if any new ones are marked "ready".
 *
 * We are careful to do these in order: obviously we respect the order the
 * Guest put them in the ring, but we also promise the Guest that they will
 * happen before any normal hypercall (which is why we check this before
 * checking for a normal hcall). */
static void do_async_hcalls(struct lguest *lg)
{
	unsigned int i;
	u8 st[LHCALL_RING_SIZE];

	/* For simplicity, we copy the entire call status array in at once. */
	if (copy_from_user(&st, &lg->lguest_data->hcall_status, sizeof(st)))
		return;

	/* We process "struct lguest_data"s hcalls[] ring once. */
	for (i = 0; i < ARRAY_SIZE(st); i++) {
		struct hcall_args args;
		/* We remember where we were up to from last time.  This makes
		 * sure that the hypercalls are done in the order the Guest
		 * places them in the ring. */
		unsigned int n = lg->next_hcall;

		/* 0xFF means there's no call here (yet). */
		if (st[n] == 0xFF)
			break;

		/* OK, we have hypercall.  Increment the "next_hcall" cursor,
		 * and wrap back to 0 if we reach the end. */
		if (++lg->next_hcall == LHCALL_RING_SIZE)
			lg->next_hcall = 0;

		/* Copy the hypercall arguments into a local copy of
		 * the hcall_args struct. */
		if (copy_from_user(&args, &lg->lguest_data->hcalls[n],
				   sizeof(struct hcall_args))) {
			kill_guest(lg, "Fetching async hypercalls");
			break;
		}

		/* Do the hypercall, same as a normal one. */
		do_hcall(lg, &args);

		/* Mark the hypercall done. */
		if (put_user(0xFF, &lg->lguest_data->hcall_status[n])) {
			kill_guest(lg, "Writing result for async hypercall");
			break;
		}

 		/* Stop doing hypercalls if we've just done a DMA to the
		 * Launcher: it needs to service this first. */
		if (lg->dma_is_pending)
			break;
	}
}

/* Last of all, we look at what happens first of all.  The very first time the
 * Guest makes a hypercall, we end up here to set things up: */
static void initialize(struct lguest *lg)
{

	/* You can't do anything until you're initialized.  The Guest knows the
	 * rules, so we're unforgiving here. */
	if (lg->hcall->arg0 != LHCALL_LGUEST_INIT) {
		kill_guest(lg, "hypercall %li before INIT", lg->hcall->arg0);
		return;
	}

	if (lguest_arch_init_hypercalls(lg))
		kill_guest(lg, "bad guest page %p", lg->lguest_data);

	/* The Guest tells us where we're not to deliver interrupts by putting
	 * the range of addresses into "struct lguest_data". */
	if (get_user(lg->noirq_start, &lg->lguest_data->noirq_start)
	    || get_user(lg->noirq_end, &lg->lguest_data->noirq_end))
		kill_guest(lg, "bad guest page %p", lg->lguest_data);

	/* We write the current time into the Guest's data page once now. */
	write_timestamp(lg);

	/* page_tables.c will also do some setup. */
	page_table_guest_data_init(lg);

	/* This is the one case where the above accesses might have been the
	 * first write to a Guest page.  This may have caused a copy-on-write
	 * fault, but the Guest might be referring to the old (read-only)
	 * page. */
	guest_pagetable_clear_all(lg);
}

/*H:100
 * Hypercalls
 *
 * Remember from the Guest, hypercalls come in two flavors: normal and
 * asynchronous.  This file handles both of types.
 */
void do_hypercalls(struct lguest *lg)
{
	/* Not initialized yet?  This hypercall must do it. */
	if (unlikely(!lg->lguest_data)) {
		/* Set up the "struct lguest_data" */
		initialize(lg);
		/* Hcall is done. */
		lg->hcall = NULL;
		return;
	}

	/* The Guest has initialized.
	 *
	 * Look in the hypercall ring for the async hypercalls: */
	do_async_hcalls(lg);

	/* If we stopped reading the hypercall ring because the Guest did a
	 * SEND_DMA to the Launcher, we want to return now.  Otherwise we do
	 * the hypercall. */
	if (!lg->dma_is_pending) {
		do_hcall(lg, lg->hcall);
		/* Tricky point: we reset the hcall pointer to mark the
		 * hypercall as "done".  We use the hcall pointer rather than
		 * the trap number to indicate a hypercall is pending.
		 * Normally it doesn't matter: the Guest will run again and
		 * update the trap number before we come back here.
		 *
		 * However, if we are signalled or the Guest sends DMA to the
		 * Launcher, the run_guest() loop will exit without running the
		 * Guest.  When it comes back it would try to re-run the
		 * hypercall. */
		lg->hcall = NULL;
	}
}

/* This routine supplies the Guest with time: it's used for wallclock time at
 * initial boot and as a rough time source if the TSC isn't available. */
void write_timestamp(struct lguest *lg)
{
	struct timespec now;
	ktime_get_real_ts(&now);
	if (copy_to_user(&lg->lguest_data->time, &now, sizeof(struct timespec)))
		kill_guest(lg, "Writing timestamp");
}