Commit 52f46079 authored by Sean Christopherson's avatar Sean Christopherson Committed by Paolo Bonzini
Browse files

KVM: x86: Further clarify the logic and comments for toggling log dirty 



Add a sanity check in kvm_mmu_slot_apply_flags to assert that the
LOG_DIRTY_PAGES flag is indeed being toggled, and explicitly rely on
that holding true when zapping collapsible SPTEs.  Manipulating the
CPU dirty log (PML) and write-protection also relies on this assertion,
but that's not obvious in the current code.

Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
Message-Id: <20210213005015.1651772-11-seanjc@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent a018eba5

arch/x86/kvm/x86.c

+11 −4
Original line number Original line Diff line number Diff line
@@ -10761,12 +10761,20 @@ static void kvm_mmu_slot_apply_flags(struct kvm *kvm, 
				     enum kvm_mr_change change)

				     enum kvm_mr_change change)

{

{

	/*

	/*

	 * Nothing to do for RO slots or CREATE/MOVE/DELETE of a slot.

	 * Nothing to do for RO slots (which can't be dirtied and can't be made

	 * See comments below.

	 * writable) or CREATE/MOVE/DELETE of a slot.  See comments below.

	 */

	 */

	if ((change != KVM_MR_FLAGS_ONLY) || (new->flags & KVM_MEM_READONLY))

	if ((change != KVM_MR_FLAGS_ONLY) || (new->flags & KVM_MEM_READONLY))

		return;

		return;





	/*

	 * READONLY and non-flags changes were filtered out above, and the only

	 * other flag is LOG_DIRTY_PAGES, i.e. something is wrong if dirty

	 * logging isn't being toggled on or off.

	 */

	if (WARN_ON_ONCE(!((old->flags ^ new->flags) & KVM_MEM_LOG_DIRTY_PAGES)))

		return;



	/*

	/*

	 * Dirty logging tracks sptes in 4k granularity, meaning that large

	 * Dirty logging tracks sptes in 4k granularity, meaning that large

	 * sptes have to be split.  If live migration is successful, the guest

	 * sptes have to be split.  If live migration is successful, the guest
@@ -10784,8 +10792,7 @@ static void kvm_mmu_slot_apply_flags(struct kvm *kvm, 
	 * MOVE/DELETE: The old mappings will already have been cleaned up by

	 * MOVE/DELETE: The old mappings will already have been cleaned up by

	 *		kvm_arch_flush_shadow_memslot()

	 *		kvm_arch_flush_shadow_memslot()

	 */

	 */

	if ((old->flags & KVM_MEM_LOG_DIRTY_PAGES) &&

	if (!(new->flags & KVM_MEM_LOG_DIRTY_PAGES))

	    !(new->flags & KVM_MEM_LOG_DIRTY_PAGES))

		kvm_mmu_zap_collapsible_sptes(kvm, new);

		kvm_mmu_zap_collapsible_sptes(kvm, new);





	/*

	/*