lguest: cache last cpu we ran on.
This optimizes the frobbing of our Switcher map.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
diff --git a/drivers/lguest/page_tables.c b/drivers/lguest/page_tables.c
index d1a5de4..19611b0 100644
--- a/drivers/lguest/page_tables.c
+++ b/drivers/lguest/page_tables.c
@@ -7,7 +7,7 @@
* converted Guest pages when running the Guest.
:*/
-/* Copyright (C) Rusty Russell IBM Corporation 2006.
+/* Copyright (C) Rusty Russell IBM Corporation 2013.
* GPL v2 and any later version */
#include <linux/mm.h>
#include <linux/gfp.h>
@@ -731,6 +731,9 @@
/* Release all the non-kernel mappings. */
flush_user_mappings(cpu->lg, next);
+ /* This hasn't run on any CPU at all. */
+ cpu->lg->pgdirs[next].last_host_cpu = -1;
+
return next;
}
@@ -790,6 +793,7 @@
for (j = 0; j < PTRS_PER_PGD; j++)
release_pgd(lg->pgdirs[i].pgdir + j);
lg->pgdirs[i].switcher_mapped = false;
+ lg->pgdirs[i].last_host_cpu = -1;
}
}
@@ -1086,37 +1090,62 @@
free_page((long)lg->pgdirs[i].pgdir);
}
+/*H:481
+ * This clears the Switcher mappings for cpu #i.
+ */
+static void remove_switcher_percpu_map(struct lg_cpu *cpu, unsigned int i)
+{
+ unsigned long base = switcher_addr + PAGE_SIZE + i * PAGE_SIZE*2;
+ pte_t *pte;
+
+ /* Clear the mappings for both pages. */
+ pte = find_spte(cpu, base, false, 0, 0);
+ release_pte(*pte);
+ set_pte(pte, __pte(0));
+
+ pte = find_spte(cpu, base + PAGE_SIZE, false, 0, 0);
+ release_pte(*pte);
+ set_pte(pte, __pte(0));
+}
+
/*H:480
* (vi) Mapping the Switcher when the Guest is about to run.
*
- * The Switcher and the two pages for this CPU need to be visible in the
- * Guest (and not the pages for other CPUs).
+ * The Switcher and the two pages for this CPU need to be visible in the Guest
+ * (and not the pages for other CPUs).
*
- * The pages have all been allocate
+ * The pages for the pagetables have all been allocated before: we just need
+ * to make sure the actual PTEs are up-to-date for the CPU we're about to run
+ * on.
*/
void map_switcher_in_guest(struct lg_cpu *cpu, struct lguest_pages *pages)
{
- unsigned long base, i;
+ unsigned long base;
struct page *percpu_switcher_page, *regs_page;
pte_t *pte;
+ struct pgdir *pgdir = &cpu->lg->pgdirs[cpu->cpu_pgd];
- /* Switcher page should always be mapped! */
- BUG_ON(!cpu->lg->pgdirs[cpu->cpu_pgd].switcher_mapped);
+ /* Switcher page should always be mapped by now! */
+ BUG_ON(!pgdir->switcher_mapped);
- /* Clear all the Switcher mappings for any other CPUs. */
- /* FIXME: This is dumb: update only when Host CPU changes. */
- for_each_possible_cpu(i) {
- /* Get location of lguest_pages (indexed by Host CPU) */
- base = switcher_addr + PAGE_SIZE
- + i * sizeof(struct lguest_pages);
+ /*
+ * Remember that we have two pages for each Host CPU, so we can run a
+ * Guest on each CPU without them interfering. We need to make sure
+ * those pages are mapped correctly in the Guest, but since we usually
+ * run on the same CPU, we cache that, and only update the mappings
+ * when we move.
+ */
+ if (pgdir->last_host_cpu == raw_smp_processor_id())
+ return;
- /* Get shadow PTE for first page (where we put guest regs). */
- pte = find_spte(cpu, base, false, 0, 0);
- set_pte(pte, __pte(0));
-
- /* This is where we put R/O state. */
- pte = find_spte(cpu, base + PAGE_SIZE, false, 0, 0);
- set_pte(pte, __pte(0));
+ /* -1 means unknown so we remove everything. */
+ if (pgdir->last_host_cpu == -1) {
+ unsigned int i;
+ for_each_possible_cpu(i)
+ remove_switcher_percpu_map(cpu, i);
+ } else {
+ /* We know exactly what CPU mapping to remove. */
+ remove_switcher_percpu_map(cpu, pgdir->last_host_cpu);
}
/*
@@ -1140,18 +1169,17 @@
* the Guest: the IDT, GDT and other things it's not supposed to
* change.
*/
- base += PAGE_SIZE;
- pte = find_spte(cpu, base, false, 0, 0);
-
+ pte = find_spte(cpu, base + PAGE_SIZE, false, 0, 0);
percpu_switcher_page
= lg_switcher_pages[1 + raw_smp_processor_id()*2 + 1];
get_page(percpu_switcher_page);
set_pte(pte, mk_pte(percpu_switcher_page,
__pgprot(__PAGE_KERNEL_RO & ~_PAGE_GLOBAL)));
-}
-/*:*/
-/*
+ pgdir->last_host_cpu = raw_smp_processor_id();
+}
+
+/*H:490
* We've made it through the page table code. Perhaps our tired brains are
* still processing the details, or perhaps we're simply glad it's over.
*