path: root/drivers/lguest/x86/core.c

/*
 * Copyright (C) 2006, Rusty Russell <rusty@rustcorp.com.au> IBM Corporation.
 * Copyright (C) 2007, Jes Sorensen <jes@sgi.com> SGI.
 *
 * 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, GOOD TITLE or
 * NON INFRINGEMENT.  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., 675 Mass Ave, Cambridge, MA 02139, USA.
 */
/*P:450
 * This file contains the x86-specific lguest code.  It used to be all
 * mixed in with drivers/lguest/core.c but several foolhardy code slashers
 * wrestled most of the dependencies out to here in preparation for porting
 * lguest to other architectures (see what I mean by foolhardy?).
 *
 * This also contains a couple of non-obvious setup and teardown pieces which
 * were implemented after days of debugging pain.
:*/
#include <linux/kernel.h>
#include <linux/start_kernel.h>
#include <linux/string.h>
#include <linux/console.h>
#include <linux/screen_info.h>
#include <linux/irq.h>
#include <linux/interrupt.h>
#include <linux/clocksource.h>
#include <linux/clockchips.h>
#include <linux/cpu.h>
#include <linux/lguest.h>
#include <linux/lguest_launcher.h>
#include <asm/paravirt.h>
#include <asm/param.h>
#include <asm/page.h>
#include <asm/pgtable.h>
#include <asm/desc.h>
#include <asm/setup.h>
#include <asm/lguest.h>
#include <asm/uaccess.h>
#include <asm/fpu/internal.h>
#include <asm/tlbflush.h>
#include "../lg.h"

static int cpu_had_pge;

static struct {
	unsigned long offset;
	unsigned short segment;
} lguest_entry;

/* Offset from where switcher.S was compiled to where we've copied it */
static unsigned long switcher_offset(void)
{
	return switcher_addr - (unsigned long)start_switcher_text;
}

/* This cpu's struct lguest_pages (after the Switcher text page) */
static struct lguest_pages *lguest_pages(unsigned int cpu)
{
	return &(((struct lguest_pages *)(switcher_addr + PAGE_SIZE))[cpu]);
}

static DEFINE_PER_CPU(struct lg_cpu *, lg_last_cpu);

/*S:010
 * We approach the Switcher.
 *
 * Remember that each CPU has two pages which are visible to the Guest when it
 * runs on that CPU.  This has to contain the state for that Guest: we copy the
 * state in just before we run the Guest.
 *
 * Each Guest has "changed" flags which indicate what has changed in the Guest
 * since it last ran.  We saw this set in interrupts_and_traps.c and
 * segments.c.
 */
static void copy_in_guest_info(struct lg_cpu *cpu, struct lguest_pages *pages)
{
	/*
	 * Copying all this data can be quite expensive.  We usually run the
	 * same Guest we ran last time (and that Guest hasn't run anywhere else
	 * meanwhile).  If that's not the case, we pretend everything in the
	 * Guest has changed.
	 */
	if (__this_cpu_read(lg_last_cpu) != cpu || cpu->last_pages != pages) {
		__this_cpu_write(lg_last_cpu, cpu);
		cpu->last_pages = pages;
		cpu->changed = CHANGED_ALL;
	}

	/*
	 * These copies are pretty cheap, so we do them unconditionally: */
	/* Save the current Host top-level page directory.
	 */
	pages->state.host_cr3 = __pa(current->mm->pgd);
	/*
	 * Set up the Guest's page tables to see this CPU's pages (and no
	 * other CPU's pages).
	 */
	map_switcher_in_guest(cpu, pages);
	/*
	 * Set up the two "TSS" members which tell the CPU what stack to use
	 * for traps which do directly into the Guest (ie. traps at privilege
	 * level 1).
	 */
	pages->state.guest_tss.sp1 = cpu->esp1;
	pages->state.guest_tss.ss1 = cpu->ss1;

	/* Copy direct-to-Guest trap entries. */
	if (cpu->changed & CHANGED_IDT)
		copy_traps(cpu, pages->state.guest_idt, default_idt_entries);

	/* Copy all GDT entries which the Guest can change. */
	if (cpu->changed & CHANGED_GDT)
		copy_gdt(cpu, pages->state.guest_gdt);
	/* If only the TLS entries have changed, copy them. */
	else if (cpu->changed & CHANGED_GDT_TLS)
		copy_gdt_tls(cpu, pages->state.guest_gdt);

	/* Mark the Guest as unchanged for next time. */
	cpu->changed = 0;
}

/* Finally: the code to actually call into the Switcher to run the Guest. */
static void run_guest_once(struct lg_cpu *cpu, struct lguest_pages *pages)
{
	/* This is a dummy value we need for GCC's sake. */
	unsigned int clobber;

	/*
	 * Copy the guest-specific information into this CPU's "struct
	 * lguest_pages".
	 */
	copy_in_guest_info(cpu, pages);

	/*
	 * Set the trap number to 256 (impossible value).  If we fault while
	 * switching to the Guest (bad segment registers or bug), this will
	 * cause us to abort the Guest.
	 */
	cpu->regs->trapnum = 256;

	/*
	 * Now: we push the "eflags" register on the stack, then do an "lcall".
	 * This is how we change from using the kernel code segment to using
	 * the dedicated lguest code segment, as well as jumping into the
	 * Switcher.
	 *
	 * The lcall also pushes the old code segment (KERNEL_CS) onto the
	 * stack, then the address of this call.  This stack layout happens to
	 * exactly match the stack layout created by an interrupt...
	 */
	asm volatile("pushf; lcall *%4"
		     /*
		      * This is how we tell GCC that %eax ("a") and %ebx ("b")
		      * are changed by this routine.  The "=" means output.
		      */
		     : "=a"(clobber), "=b"(clobber)
		     /*
		      * %eax contains the pages pointer.  ("0" refers to the
		      * 0-th argument above, ie "a").  %ebx contains the
		      * physical address of the Guest's top-level page
		      * directory.
		      */
		     : "0"(pages), 
		       "1"(__pa(cpu->lg->pgdirs[cpu->cpu_pgd].pgdir)),
		       "m"(lguest_entry)
		     /*
		      * We tell gcc that all these registers could change,
		      * which means we don't have to save and restore them in
		      * the Switcher.
		      */
		     : "memory", "%edx", "%ecx", "%edi", "%esi");
}
/*:*/

unsigned long *lguest_arch_regptr(struct lg_cpu *cpu, size_t reg_off, bool any)
{
	switch (reg_off) {
	case offsetof(struct pt_regs, bx):
		return &cpu->regs->ebx;
	case offsetof(struct pt_regs, cx):
		return &cpu->regs->ecx;
	case offsetof(struct pt_regs, dx):
		return &cpu->regs->edx;
	case offsetof(struct pt_regs, si):
		return &cpu->regs->esi;
	case offsetof(struct pt_regs, di):
		return &cpu->regs->edi;
	case offsetof(struct pt_regs, bp):
		return &cpu->regs->ebp;
	case offsetof(struct pt_regs, ax):
		return &cpu->regs->eax;
	case offsetof(struct pt_regs, ip):
		return &cpu->regs->eip;
	case offsetof(struct pt_regs, sp):
		return &cpu->regs->esp;
	}

	/* Launcher can read these, but we don't allow any setting. */
	if (any) {
		switch (reg_off) {
		case offsetof(struct pt_regs, ds):
			return &cpu->regs->ds;
		case offsetof(struct pt_regs, es):
			return &cpu->regs->es;
		case offsetof(struct pt_regs, fs):
			return &cpu->regs->fs;
		case offsetof(struct pt_regs, gs):
			return &cpu->regs->gs;
		case offsetof(struct pt_regs, cs):
			return &cpu->regs->cs;
		case offsetof(struct pt_regs, flags):
			return &cpu->regs->eflags;
		case offsetof(struct pt_regs, ss):
			return &