# HG changeset patch
# User George Dunlap <gdunlap@xxxxxxxxxxxxx>
# Date 1190199484 -3600
# Node ID 91a5b7eaede33414a6bade9ef50c9b2d1ffa4686
# Parent fadd1f8222b3fc3e41977863825871dbc8514344
[shadow] Be smarter about what we check to avoid unnecessary brute-force
searches
The old code checked only if the page was still a pagetable before
doing a brute-force search, rather than checking if it was still
shadowed as the type indicated. This meant that if a page was shadowed
as two different types, it was guaranteed to do a full brute-force search
even if all references could be found by up-pointers.
This checks the proper thing so that it will only do a brute-force if
necessary.
It also re-orders the unshadows so that higher levels are done first. In
many cases, lower-level shadows will be destroyed in the process of
higher-level shadows being destroyed, again saving brute-force searches.
---
xen/arch/x86/mm/shadow/common.c | 59 +++++++++++++++++++++-------------------
1 files changed, 31 insertions(+), 28 deletions(-)
diff -r fadd1f8222b3 -r 91a5b7eaede3 xen/arch/x86/mm/shadow/common.c
--- a/xen/arch/x86/mm/shadow/common.c Wed Sep 19 11:42:05 2007 +0100
+++ b/xen/arch/x86/mm/shadow/common.c Wed Sep 19 11:58:04 2007 +0100
@@ -1981,7 +1981,6 @@ void sh_remove_shadows(struct vcpu *v, m
{
struct page_info *pg = mfn_to_page(gmfn);
mfn_t smfn;
- u32 sh_flags;
int do_locking;
unsigned char t;
@@ -2065,42 +2064,46 @@ void sh_remove_shadows(struct vcpu *v, m
/* Search for this shadow in all appropriate shadows */
perfc_incr(shadow_unshadow);
- sh_flags = pg->shadow_flags;
/* Lower-level shadows need to be excised from upper-level shadows.
* This call to hash_foreach() looks dangerous but is in fact OK: each
* call will remove at most one shadow, and terminate immediately when
* it does remove it, so we never walk the hash after doing a deletion. */
-#define DO_UNSHADOW(_type) do { \
- t = (_type); \
- smfn = shadow_hash_lookup(v, mfn_x(gmfn), t); \
- if ( unlikely(!mfn_valid(smfn)) ) \
- { \
- SHADOW_ERROR(": gmfn %#lx has flags 0x%"PRIx32 \
- " but no type-0x%"PRIx32" shadow\n", \
- mfn_x(gmfn), sh_flags, t); \
- break; \
- } \
- if ( sh_type_is_pinnable(v, t) ) \
- sh_unpin(v, smfn); \
- else \
- sh_remove_shadow_via_pointer(v, smfn); \
- if ( (pg->count_info & PGC_page_table) && !fast ) \
- hash_foreach(v, masks[t], callbacks, smfn); \
+#define DO_UNSHADOW(_type) do { \
+ t = (_type); \
+ if( !(pg->count_info & PGC_page_table) \
+ || !(pg->shadow_flags & (1 << t)) ) \
+ break; \
+ smfn = shadow_hash_lookup(v, mfn_x(gmfn), t); \
+ if ( unlikely(!mfn_valid(smfn)) ) \
+ { \
+ SHADOW_ERROR(": gmfn %#lx has flags 0x%"PRIx32 \
+ " but no type-0x%"PRIx32" shadow\n", \
+ mfn_x(gmfn), (uint32_t)pg->shadow_flags, t); \
+ break; \
+ } \
+ if ( sh_type_is_pinnable(v, t) ) \
+ sh_unpin(v, smfn); \
+ else \
+ sh_remove_shadow_via_pointer(v, smfn); \
+ if( !fast \
+ && (pg->count_info & PGC_page_table) \
+ && (pg->shadow_flags & (1 << t)) ) \
+ hash_foreach(v, masks[t], callbacks, smfn); \
} while (0)
- if ( sh_flags & SHF_L1_32 ) DO_UNSHADOW(SH_type_l1_32_shadow);
- if ( sh_flags & SHF_L2_32 ) DO_UNSHADOW(SH_type_l2_32_shadow);
+ DO_UNSHADOW(SH_type_l2_32_shadow);
+ DO_UNSHADOW(SH_type_l1_32_shadow);
#if CONFIG_PAGING_LEVELS >= 3
- if ( sh_flags & SHF_L1_PAE ) DO_UNSHADOW(SH_type_l1_pae_shadow);
- if ( sh_flags & SHF_L2_PAE ) DO_UNSHADOW(SH_type_l2_pae_shadow);
- if ( sh_flags & SHF_L2H_PAE ) DO_UNSHADOW(SH_type_l2h_pae_shadow);
+ DO_UNSHADOW(SH_type_l2h_pae_shadow);
+ DO_UNSHADOW(SH_type_l2_pae_shadow);
+ DO_UNSHADOW(SH_type_l1_pae_shadow);
#if CONFIG_PAGING_LEVELS >= 4
- if ( sh_flags & SHF_L1_64 ) DO_UNSHADOW(SH_type_l1_64_shadow);
- if ( sh_flags & SHF_L2_64 ) DO_UNSHADOW(SH_type_l2_64_shadow);
- if ( sh_flags & SHF_L2H_64 ) DO_UNSHADOW(SH_type_l2h_64_shadow);
- if ( sh_flags & SHF_L3_64 ) DO_UNSHADOW(SH_type_l3_64_shadow);
- if ( sh_flags & SHF_L4_64 ) DO_UNSHADOW(SH_type_l4_64_shadow);
+ DO_UNSHADOW(SH_type_l4_64_shadow);
+ DO_UNSHADOW(SH_type_l3_64_shadow);
+ DO_UNSHADOW(SH_type_l2h_64_shadow);
+ DO_UNSHADOW(SH_type_l2_64_shadow);
+ DO_UNSHADOW(SH_type_l1_64_shadow);
#endif
#endif
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