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KVM: MMU: do not write-protect large mappings

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There is not much point in write protecting large mappings. This
can only happen when a page is shadowed during the window between
is_largepage_backed and mmu_lock acquision. Zap the entry instead, so
the next pagefault will find a shadowed page via is_largepage_backed and
fallback to 4k translations.

Simplifies out of sync shadow.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
This commit is contained in:
Marcelo Tosatti 2008-09-23 13:18:32 -03:00 committed by Avi Kivity
parent a378b4e64c
commit 38187c830c
1 changed files with 8 additions and 2 deletions
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10
arch/x86/kvm/mmu.c
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@ -1180,11 +1180,16 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *shadow_pte,
|| (write_fault && !is_write_protection(vcpu) && !user_fault)) {
struct kvm_mmu_page *shadow;
if (largepage && has_wrprotected_page(vcpu->kvm, gfn)) {
ret = 1;
spte = shadow_trap_nonpresent_pte;
goto set_pte;
}
spte |= PT_WRITABLE_MASK;
shadow = kvm_mmu_lookup_page(vcpu->kvm, gfn);
if (shadow ||
(largepage && has_wrprotected_page(vcpu->kvm, gfn))) {
if (shadow) {
pgprintk("%s: found shadow page for %lx, marking ro\n",
__func__, gfn);
ret = 1;
@ -1197,6 +1202,7 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *shadow_pte,
if (pte_access & ACC_WRITE_MASK)
mark_page_dirty(vcpu->kvm, gfn);
set_pte:
set_shadow_pte(shadow_pte, spte);
return ret;
}