xcp-1.6-updates/xen-4.1.hg
changeset 23249:b5051d40e1cc
x86/mm/shadow: adjust early-unshadow heuristic for PAE guests.
PAE guests have 8-byte PTEs but tend to clear memory with 4-byte
writes.
This means that when zeroing a former pagetable every second 4-byte
write is unaligned and so the consecutive-zeroes --> unshadow
heuristic never kicks in. Adjust the heuristic not to reset when
a write is >= 4 bytes and writing zero but not PTE-aligned.
Signed-off-by: Tim Deegan <Tim.Deegan@citrix.com>
xen-unstable changeset: 23554:c91255b2f0a0
xen-unstable date: Mon Jun 20 13:16:14 2011 +0100
PAE guests have 8-byte PTEs but tend to clear memory with 4-byte
writes.
This means that when zeroing a former pagetable every second 4-byte
write is unaligned and so the consecutive-zeroes --> unshadow
heuristic never kicks in. Adjust the heuristic not to reset when
a write is >= 4 bytes and writing zero but not PTE-aligned.
Signed-off-by: Tim Deegan <Tim.Deegan@citrix.com>
xen-unstable changeset: 23554:c91255b2f0a0
xen-unstable date: Mon Jun 20 13:16:14 2011 +0100
| author | Tim Deegan <Tim.Deegan@citrix.com> |
|---|---|
| date | Wed Mar 07 09:22:58 2012 +0000 (2012-03-07) |
| parents | b0bf2fc4eff9 |
| children | a168569a7659 |
| files | xen/arch/x86/mm/shadow/multi.c |
line diff
1.1 --- a/xen/arch/x86/mm/shadow/multi.c Wed Mar 07 08:43:28 2012 +0000 1.2 +++ b/xen/arch/x86/mm/shadow/multi.c Wed Mar 07 09:22:58 2012 +0000 1.3 @@ -4943,11 +4943,14 @@ static void emulate_unmap_dest(struct vc 1.4 ASSERT(mfn_valid(sh_ctxt->mfn1)); 1.5 1.6 /* If we are writing lots of PTE-aligned zeros, might want to unshadow */ 1.7 - if ( likely(bytes >= 4) 1.8 - && (*(u32 *)addr == 0) 1.9 - && ((unsigned long) addr & ((sizeof (guest_intpte_t)) - 1)) == 0 ) 1.10 - check_for_early_unshadow(v, sh_ctxt->mfn1); 1.11 - else 1.12 + if ( likely(bytes >= 4) && (*(u32 *)addr == 0) ) 1.13 + { 1.14 + if ( ((unsigned long) addr & ((sizeof (guest_intpte_t)) - 1)) == 0 ) 1.15 + check_for_early_unshadow(v, sh_ctxt->mfn1); 1.16 + /* Don't reset the heuristic if we're writing zeros at non-aligned 1.17 + * addresses, otherwise it doesn't catch REP MOVSD on PAE guests */ 1.18 + } 1.19 + else 1.20 reset_early_unshadow(v); 1.21 1.22 /* We can avoid re-verifying the page contents after the write if: