lguest: cache last cpu we ran on.

This optimizes the frobbing of our Switcher map.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

2 files changed, 54 insertions, 25 deletions

diff --git a/drivers/lguest/lg.h b/drivers/lguest/lg.h
index 005929a3fd52..2eef40be4c04 100644
--- a/drivers/lguest/lg.h
+++ b/drivers/lguest/lg.h
@@ -17,6 +17,7 @@
 struct pgdir {
         unsigned long gpgdir;
         bool switcher_mapped;
+        int last_host_cpu;
         pgd_t *pgdir;
 };
 
diff --git a/drivers/lguest/page_tables.c b/drivers/lguest/page_tables.c
index d1a5de45be02..19611b0551cd 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 @@ static unsigned int new_pgdir(struct lg_cpu *cpu,
         /* 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 @@ static void release_all_pagetables(struct lguest *lg)
                 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 @@ void free_guest_pagetable(struct lguest *lg)
                 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);
-
-        /* 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);
+        /* Switcher page should always be mapped by now! */
+        BUG_ON(!pgdir->switcher_mapped);
 
-                /* Get shadow PTE for first page (where we put guest regs). */
-                pte = find_spte(cpu, base, false, 0, 0);
-                set_pte(pte, __pte(0));
+        /* 
+         * 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;
 
-                /* 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 @@ void map_switcher_in_guest(struct lg_cpu *cpu, struct lguest_pages *pages)
          * 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.
  *