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/lg.h b/drivers/lguest/lg.h
index 005929a..2eef40b 100644 (file)
--- 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 d1a5de4..19611b0 100644 (file)
--- 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.
  *