# HG changeset patch
# User Tim Deegan <tim.deegan@xxxxxxxxxxxxx>
# Node ID 4fdcccd2235213f32e7b2a37cd09206d0c710701
# Parent bd2be8a8fc7286f44d9fbde172e4a1bacf5cc739
[XEN] Fix race in shadow invlpg
This fixes a crash under mmstress in SMP linux guests, where one vcpu
could remove shadow entries when another was reading them for invlpg.
Signed-off-by: Tim Deegan <Tim.Deegan@xxxxxxxxxxxxx>
---
xen/arch/x86/mm/shadow/multi.c | 134 ++++++++++++++-------------------------
xen/include/asm-x86/perfc_defn.h | 4 -
2 files changed, 53 insertions(+), 85 deletions(-)
diff -r bd2be8a8fc72 -r 4fdcccd22352 xen/arch/x86/mm/shadow/multi.c
--- a/xen/arch/x86/mm/shadow/multi.c Thu Oct 12 10:56:41 2006 +0100
+++ b/xen/arch/x86/mm/shadow/multi.c Thu Oct 12 11:08:48 2006 +0100
@@ -1375,80 +1375,6 @@ static int shadow_set_l1e(struct vcpu *v
/**************************************************************************/
-/* These functions take a vcpu and a virtual address, and return a pointer
- * to the appropriate level N entry from the shadow tables.
- * If the necessary tables are not present in the shadow, they return NULL. */
-
-/* N.B. The use of GUEST_PAGING_LEVELS here is correct. If the shadow has
- * more levels than the guest, the upper levels are always fixed and do not
- * reflect any information from the guest, so we do not use these functions
- * to access them. */
-
-#if GUEST_PAGING_LEVELS >= 4
-static shadow_l4e_t *
-shadow_get_l4e(struct vcpu *v, unsigned long va)
-{
- /* Reading the top level table is always valid. */
- return sh_linear_l4_table(v) + shadow_l4_linear_offset(va);
-}
-#endif /* GUEST_PAGING_LEVELS >= 4 */
-
-
-#if GUEST_PAGING_LEVELS >= 3
-static shadow_l3e_t *
-shadow_get_l3e(struct vcpu *v, unsigned long va)
-{
-#if GUEST_PAGING_LEVELS >= 4 /* 64bit... */
- /* Get the l4 */
- shadow_l4e_t *sl4e = shadow_get_l4e(v, va);
- ASSERT(sl4e != NULL);
- if ( !(shadow_l4e_get_flags(*sl4e) & _PAGE_PRESENT) )
- return NULL;
- ASSERT(valid_mfn(shadow_l4e_get_mfn(*sl4e)));
- /* l4 was present; OK to get the l3 */
- return sh_linear_l3_table(v) + shadow_l3_linear_offset(va);
-#else /* PAE... */
- /* Top level is always mapped */
- ASSERT(v->arch.shadow_vtable);
- return ((shadow_l3e_t *)v->arch.shadow_vtable) +
shadow_l3_linear_offset(va);
-#endif
-}
-#endif /* GUEST_PAGING_LEVELS >= 3 */
-
-
-static shadow_l2e_t *
-shadow_get_l2e(struct vcpu *v, unsigned long va)
-{
-#if GUEST_PAGING_LEVELS >= 3 /* 64bit/PAE... */
- /* Get the l3 */
- shadow_l3e_t *sl3e = shadow_get_l3e(v, va);
- if ( sl3e == NULL || !(shadow_l3e_get_flags(*sl3e) & _PAGE_PRESENT) )
- return NULL;
- ASSERT(valid_mfn(shadow_l3e_get_mfn(*sl3e)));
- /* l3 was present; OK to get the l2 */
-#endif
- return sh_linear_l2_table(v) + shadow_l2_linear_offset(va);
-}
-
-
-#if 0 // avoid the compiler warning for now...
-
-static shadow_l1e_t *
-shadow_get_l1e(struct vcpu *v, unsigned long va)
-{
- /* Get the l2 */
- shadow_l2e_t *sl2e = shadow_get_l2e(v, va);
- if ( sl2e == NULL || !(shadow_l2e_get_flags(*sl2e) & _PAGE_PRESENT) )
- return NULL;
- ASSERT(valid_mfn(shadow_l2e_get_mfn(*sl2e)));
- /* l2 was present; OK to get the l1 */
- return sh_linear_l1_table(v) + shadow_l1_linear_offset(va);
-}
-
-#endif
-
-
-/**************************************************************************/
/* Macros to walk pagetables. These take the shadow of a pagetable and
* walk every "interesting" entry. That is, they don't touch Xen mappings,
* and for 32-bit l2s shadowed onto PAE or 64-bit, they only touch every
@@ -2050,6 +1976,12 @@ sh_make_monitor_table(struct vcpu *v)
* they are needed. The "demand" argument is non-zero when handling
* a demand fault (so we know what to do about accessed bits &c).
* If the necessary tables are not present in the guest, they return NULL. */
+
+/* N.B. The use of GUEST_PAGING_LEVELS here is correct. If the shadow has
+ * more levels than the guest, the upper levels are always fixed and do not
+ * reflect any information from the guest, so we do not use these functions
+ * to access them. */
+
#if GUEST_PAGING_LEVELS >= 4
static shadow_l4e_t * shadow_get_and_create_l4e(struct vcpu *v,
walk_t *gw,
@@ -3223,26 +3155,62 @@ sh_invlpg(struct vcpu *v, unsigned long
* instruction should be issued on the hardware, or 0 if it's safe not
* to do so. */
{
- shadow_l2e_t *ptr_sl2e = shadow_get_l2e(v, va);
-
- // XXX -- might be a good thing to prefetch the va into the shadow
-
- // no need to flush anything if there's no SL2...
- //
- if ( !ptr_sl2e )
+ shadow_l2e_t sl2e;
+
+ perfc_incrc(shadow_invlpg);
+
+ /* First check that we can safely read the shadow l2e. SMP/PAE linux can
+ * run as high as 6% of invlpg calls where we haven't shadowed the l2
+ * yet. */
+#if SHADOW_PAGING_LEVELS == 4
+ {
+ shadow_l3e_t sl3e;
+ if ( !(shadow_l4e_get_flags(
+ sh_linear_l4_table(v)[shadow_l4_linear_offset(va)])
+ & _PAGE_PRESENT) )
+ return 0;
+ /* This must still be a copy-from-user because we don't have the
+ * shadow lock, and the higher-level shadows might disappear
+ * under our feet. */
+ if ( __copy_from_user(&sl3e, (sh_linear_l3_table(v)
+ + shadow_l3_linear_offset(va)),
+ sizeof (sl3e)) != 0 )
+ {
+ perfc_incrc(shadow_invlpg_fault);
+ return 0;
+ }
+ if ( (!shadow_l3e_get_flags(sl3e) & _PAGE_PRESENT) )
+ return 0;
+ }
+#elif SHADOW_PAGING_LEVELS == 3
+ if ( !(shadow_l3e_get_flags(
+ ((shadow_l3e_t *)v->arch.shadow_vtable)[shadow_l3_linear_offset(va)])
+ & _PAGE_PRESENT) )
+ // no need to flush anything if there's no SL2...
return 0;
+#endif
+
+ /* This must still be a copy-from-user because we don't have the shadow
+ * lock, and the higher-level shadows might disappear under our feet. */
+ if ( __copy_from_user(&sl2e,
+ sh_linear_l2_table(v) + shadow_l2_linear_offset(va),
+ sizeof (sl2e)) != 0 )
+ {
+ perfc_incrc(shadow_invlpg_fault);
+ return 0;
+ }
// If there's nothing shadowed for this particular sl2e, then
// there is no need to do an invlpg, either...
//
- if ( !(shadow_l2e_get_flags(*ptr_sl2e) & _PAGE_PRESENT) )
+ if ( !(shadow_l2e_get_flags(sl2e) & _PAGE_PRESENT) )
return 0;
// Check to see if the SL2 is a splintered superpage...
// If so, then we'll need to flush the entire TLB (because that's
// easier than invalidating all of the individual 4K pages).
//
- if ( (mfn_to_page(shadow_l2e_get_mfn(*ptr_sl2e))->count_info &
+ if ( (mfn_to_page(shadow_l2e_get_mfn(sl2e))->count_info &
PGC_SH_type_mask) == PGC_SH_fl1_shadow )
{
local_flush_tlb();
diff -r bd2be8a8fc72 -r 4fdcccd22352 xen/include/asm-x86/perfc_defn.h
--- a/xen/include/asm-x86/perfc_defn.h Thu Oct 12 10:56:41 2006 +0100
+++ b/xen/include/asm-x86/perfc_defn.h Thu Oct 12 11:08:48 2006 +0100
@@ -81,8 +81,8 @@ PERFCOUNTER_CPU(shadow_unshadow_bf, "
PERFCOUNTER_CPU(shadow_unshadow_bf, "shadow unshadow brute-force")
PERFCOUNTER_CPU(shadow_get_page_fail, "shadow_get_page_from_l1e failed")
PERFCOUNTER_CPU(shadow_guest_walk, "shadow walks guest tables")
-PERFCOUNTER_CPU(shadow_walk_cache_hit, "shadow walk-cache hits")
-PERFCOUNTER_CPU(shadow_walk_cache_miss, "shadow walk-cache misses")
+PERFCOUNTER_CPU(shadow_invlpg, "shadow emulates invlpg")
+PERFCOUNTER_CPU(shadow_invlpg_fault, "shadow invlpg faults")
/*#endif*/ /* __XEN_PERFC_DEFN_H__ */
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