Commit 07dc4f35 authored by Sean Christopherson's avatar Sean Christopherson Committed by Paolo Bonzini
Browse files

KVM: x86/mmu: comment on kvm_mmu_get_page's syncing of pages 



Explain the usage of sync_page() in kvm_mmu_get_page(), which is
subtle in how and why it differs from mmu_sync_children().

Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
[Split out of a different patch by Sean. - Paolo]
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 2640b086

arch/x86/kvm/mmu/mmu.c

+11 −2
Original line number Diff line number Diff line
@@ -2008,8 +2008,17 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu, 
			goto trace_get_page;



		if (sp->unsync) {

			/* The page is good, but __kvm_sync_page might still end

			 * up zapping it.  If so, break in order to rebuild it.

			/*

			 * The page is good, but is stale.  __kvm_sync_page does

			 * get the latest guest state, but (unlike mmu_unsync_children)

			 * it doesn't write-protect the page or mark it synchronized!

			 * This way the validity of the mapping is ensured, but the

			 * overhead of write protection is not incurred until the

			 * guest invalidates the TLB mapping.  This allows multiple

			 * SPs for a single gfn to be unsync.

			 *

			 * If the sync fails, the page is zapped.  If so, break

			 * in order to rebuild it.

			 */

			if (!__kvm_sync_page(vcpu, sp, &invalid_list))

				break;