Exemple #1
0
/*H:410
 * Updating a PTE entry is a little trickier.
 *
 * We keep track of several different page tables (the Guest uses one for each
 * process, so it makes sense to cache at least a few).  Each of these have
 * identical kernel parts: ie. every mapping above PAGE_OFFSET is the same for
 * all processes.  So when the page table above that address changes, we update
 * all the page tables, not just the current one.  This is rare.
 *
 * The benefit is that when we have to track a new page table, we can keep all
 * the kernel mappings.  This speeds up context switch immensely.
 */
void guest_set_pte(struct lg_cpu *cpu,
		   unsigned long gpgdir, unsigned long vaddr, pte_t gpte)
{
	/* We don't let you remap the Switcher; we need it to get back! */
	if (vaddr >= switcher_addr) {
		kill_guest(cpu, "attempt to set pte into Switcher pages");
		return;
	}

	/*
	 * Kernel mappings must be changed on all top levels.  Slow, but doesn't
	 * happen often.
	 */
	if (vaddr >= cpu->lg->kernel_address) {
		unsigned int i;
		for (i = 0; i < ARRAY_SIZE(cpu->lg->pgdirs); i++)
			if (cpu->lg->pgdirs[i].pgdir)
				__guest_set_pte(cpu, i, vaddr, gpte);
	} else {
		/* Is this page table one we have a shadow for? */
		int pgdir = find_pgdir(cpu->lg, gpgdir);
		if (pgdir != ARRAY_SIZE(cpu->lg->pgdirs))
			/* If so, do the update. */
			__guest_set_pte(cpu, pgdir, vaddr, gpte);
	}
}
Exemple #2
0
/*H:430
 * (iv) Switching page tables
 *
 * Now we've seen all the page table setting and manipulation, let's see
 * what happens when the Guest changes page tables (ie. changes the top-level
 * pgdir).  This occurs on almost every context switch.
 */
void guest_new_pagetable(struct lg_cpu *cpu, unsigned long pgtable)
{
	int newpgdir, repin = 0;

	/*
	 * The very first time they call this, we're actually running without
	 * any page tables; we've been making it up.  Throw them away now.
	 */
	if (unlikely(cpu->linear_pages)) {
		release_all_pagetables(cpu->lg);
		cpu->linear_pages = false;
		/* Force allocation of a new pgdir. */
		newpgdir = ARRAY_SIZE(cpu->lg->pgdirs);
	} else {
		/* Look to see if we have this one already. */
		newpgdir = find_pgdir(cpu->lg, pgtable);
	}

	/*
	 * If not, we allocate or mug an existing one: if it's a fresh one,
	 * repin gets set to 1.
	 */
	if (newpgdir == ARRAY_SIZE(cpu->lg->pgdirs))
		newpgdir = new_pgdir(cpu, pgtable, &repin);
	/* Change the current pgd index to the new one. */
	cpu->cpu_pgd = newpgdir;
	/* If it was completely blank, we map in the Guest kernel stack */
	if (repin)
		pin_stack_pages(cpu);
}
Exemple #3
0
/*H:400
 * (iii) Setting up a page table entry when the Guest tells us one has changed.
 *
 * Just like we did in interrupts_and_traps.c, it makes sense for us to deal
 * with the other side of page tables while we're here: what happens when the
 * Guest asks for a page table to be updated?
 *
 * We already saw that demand_page() will fill in the shadow page tables when
 * needed, so we can simply remove shadow page table entries whenever the Guest
 * tells us they've changed.  When the Guest tries to use the new entry it will
 * fault and demand_page() will fix it up.
 *
 * So with that in mind here's our code to update a (top-level) PGD entry:
 */
void guest_set_pgd(struct lguest *lg, unsigned long gpgdir, u32 idx)
{
	int pgdir;

	if (idx >= SWITCHER_PGD_INDEX)
		return;

	/* If they're talking about a page table we have a shadow for... */
	pgdir = find_pgdir(lg, gpgdir);
	if (pgdir < ARRAY_SIZE(lg->pgdirs))
		/* ... throw it away. */
		release_pgd(lg->pgdirs[pgdir].pgdir + idx);
}
Exemple #4
0
/*H:410
 * Updating a PTE entry is a little trickier.
 *
 * We keep track of several different page tables (the Guest uses one for each
 * process, so it makes sense to cache at least a few).  Each of these have
 * identical kernel parts: ie. every mapping above PAGE_OFFSET is the same for
 * all processes.  So when the page table above that address changes, we update
 * all the page tables, not just the current one.  This is rare.
 *
 * The benefit is that when we have to track a new page table, we can keep all
 * the kernel mappings.  This speeds up context switch immensely.
 */
void guest_set_pte(struct lg_cpu *cpu,
		   unsigned long gpgdir, unsigned long vaddr, pte_t gpte)
{
	/*
	 * Kernel mappings must be changed on all top levels.  Slow, but doesn't
	 * happen often.
	 */
	if (vaddr >= cpu->lg->kernel_address) {
		unsigned int i;
		for (i = 0; i < ARRAY_SIZE(cpu->lg->pgdirs); i++)
			if (cpu->lg->pgdirs[i].pgdir)
				do_set_pte(cpu, i, vaddr, gpte);
	} else {
		/* Is this page table one we have a shadow for? */
		int pgdir = find_pgdir(cpu->lg, gpgdir);
		if (pgdir != ARRAY_SIZE(cpu->lg->pgdirs))
			/* If so, do the update. */
			do_set_pte(cpu, pgdir, vaddr, gpte);
	}
}
Exemple #5
0
/*H:400
 * (iii) Setting up a page table entry when the Guest tells us one has changed.
 *
 * Just like we did in interrupts_and_traps.c, it makes sense for us to deal
 * with the other side of page tables while we're here: what happens when the
 * Guest asks for a page table to be updated?
 *
 * We already saw that demand_page() will fill in the shadow page tables when
 * needed, so we can simply remove shadow page table entries whenever the Guest
 * tells us they've changed.  When the Guest tries to use the new entry it will
 * fault and demand_page() will fix it up.
 *
 * So with that in mind here's our code to update a (top-level) PGD entry:
 */
void guest_set_pgd(struct lguest *lg, unsigned long gpgdir, u32 idx)
{
	int pgdir;

	if (idx > PTRS_PER_PGD) {
		kill_guest(&lg->cpus[0], "Attempt to set pgd %u/%u",
			   idx, PTRS_PER_PGD);
		return;
	}

	/* If they're talking about a page table we have a shadow for... */
	pgdir = find_pgdir(lg, gpgdir);
	if (pgdir < ARRAY_SIZE(lg->pgdirs)) {
		/* ... throw it away. */
		release_pgd(lg->pgdirs[pgdir].pgdir + idx);
		/* That might have been the Switcher mapping, remap it. */
		if (!allocate_switcher_mapping(&lg->cpus[0])) {
			kill_guest(&lg->cpus[0],
				   "Cannot populate switcher mapping");
		}
		lg->pgdirs[pgdir].last_host_cpu = -1;
	}
}