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Commit 38187c83 authored by Marcelo Tosatti's avatar Marcelo Tosatti Committed by Avi Kivity
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KVM: MMU: do not write-protect large mappings 



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: default avatarMarcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: default avatarAvi Kivity <avi@redhat.com>
parent a378b4e6

arch/x86/kvm/mmu.c

+8 −2
Original line number Diff line number Diff line
@@ -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;

}