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KVM: Assume that writes smaller than 4 bytes are to non-pagetable pages 

This allows us to remove write protection earlier than otherwise.  Should
some mad OS choose to use byte writes to update pagetables, it will suffer
a performance hit, but still work correctly.

Signed-off-by: Avi Kivity <avi@qumranet.com>
This commit is contained in:
Avi Kivity 2007-04-30 14:47:02 +03:00
parent c86813393f
commit e925c5ba93
1 changed files with 1 additions and 0 deletions
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1
drivers/kvm/mmu.c
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@ -1169,6 +1169,7 @@ void kvm_mmu_pre_write(struct kvm_vcpu *vcpu, gpa_t gpa, int bytes)
continue; continue;
pte_size = page->role.glevels == PT32_ROOT_LEVEL ? 4 : 8; pte_size = page->role.glevels == PT32_ROOT_LEVEL ? 4 : 8;
misaligned = (offset ^ (offset + bytes - 1)) & ~(pte_size - 1); misaligned = (offset ^ (offset + bytes - 1)) & ~(pte_size - 1);
misaligned |= bytes < 4;
if (misaligned || flooded) { if (misaligned || flooded) {
/* /*
* Misaligned accesses are too much trouble to fix * Misaligned accesses are too much trouble to fix