/*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);
}
}
/*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);
}
/*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);
}
/*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);
}
}
/*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;
}
}