lguest: map Switcher text whenever we allocate a new pagetable.
It's always to same, so no need to put in the PTE every time we're
about to run. Keep a flag to track whether the pagetable has the
Switcher entries allocated, and when allocating always initialize the
Switcher text PTE.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
diff --git a/drivers/lguest/lg.h b/drivers/lguest/lg.h
index faac9fc..005929a 100644
--- a/drivers/lguest/lg.h
+++ b/drivers/lguest/lg.h
@@ -16,6 +16,7 @@
struct pgdir {
unsigned long gpgdir;
+ bool switcher_mapped;
pgd_t *pgdir;
};
diff --git a/drivers/lguest/page_tables.c b/drivers/lguest/page_tables.c
index 1f48f27..d1a5de4 100644
--- a/drivers/lguest/page_tables.c
+++ b/drivers/lguest/page_tables.c
@@ -736,18 +736,39 @@
/*H:501
* We do need the Switcher code mapped at all times, so we allocate that
- * part of the Guest page table here, and populate it when we're about to run
- * the guest.
+ * part of the Guest page table here. We map the Switcher code immediately,
+ * but defer mapping of the guest register page and IDT/LDT etc page until
+ * just before we run the guest in map_switcher_in_guest().
+ *
+ * We *could* do this setup in map_switcher_in_guest(), but at that point
+ * we've interrupts disabled, and allocating pages like that is fraught: we
+ * can't sleep if we need to free up some memory.
*/
static bool allocate_switcher_mapping(struct lg_cpu *cpu)
{
int i;
for (i = 0; i < TOTAL_SWITCHER_PAGES; i++) {
- if (!find_spte(cpu, switcher_addr + i * PAGE_SIZE, true,
- CHECK_GPGD_MASK, _PAGE_TABLE))
+ pte_t *pte = find_spte(cpu, switcher_addr + i * PAGE_SIZE, true,
+ CHECK_GPGD_MASK, _PAGE_TABLE);
+ if (!pte)
return false;
+
+ /*
+ * Map the switcher page if not already there. It might
+ * already be there because we call allocate_switcher_mapping()
+ * in guest_set_pgd() just in case it did discard our Switcher
+ * mapping, but it probably didn't.
+ */
+ if (i == 0 && !(pte_flags(*pte) & _PAGE_PRESENT)) {
+ /* Get a reference to the Switcher page. */
+ get_page(lg_switcher_pages[0]);
+ /* Create a read-only, exectuable, kernel-style PTE */
+ set_pte(pte,
+ mk_pte(lg_switcher_pages[0], PAGE_KERNEL_RX));
+ }
}
+ cpu->lg->pgdirs[cpu->cpu_pgd].switcher_mapped = true;
return true;
}
@@ -768,6 +789,7 @@
/* Every PGD entry. */
for (j = 0; j < PTRS_PER_PGD; j++)
release_pgd(lg->pgdirs[i].pgdir + j);
+ lg->pgdirs[i].switcher_mapped = false;
}
}
@@ -827,8 +849,10 @@
if (repin)
pin_stack_pages(cpu);
- if (!allocate_switcher_mapping(cpu))
- kill_guest(cpu, "Cannot populate switcher mapping");
+ if (!cpu->lg->pgdirs[cpu->cpu_pgd].switcher_mapped) {
+ if (!allocate_switcher_mapping(cpu))
+ kill_guest(cpu, "Cannot populate switcher mapping");
+ }
}
/*:*/
@@ -1076,10 +1100,8 @@
struct page *percpu_switcher_page, *regs_page;
pte_t *pte;
- /* Code page should always be mapped, and executable. */
- pte = find_spte(cpu, switcher_addr, false, 0, 0);
- get_page(lg_switcher_pages[0]);
- set_pte(pte, mk_pte(lg_switcher_pages[0], PAGE_KERNEL_RX));
+ /* Switcher page should always be mapped! */
+ BUG_ON(!cpu->lg->pgdirs[cpu->cpu_pgd].switcher_mapped);
/* Clear all the Switcher mappings for any other CPUs. */
/* FIXME: This is dumb: update only when Host CPU changes. */