Commit 4b442955 authored Jun 02, 2020 by Anthony Yznaga Committed by Paolo Bonzini Jun 04, 2020

KVM: x86: avoid unnecessary rmap walks when creating/moving slots

On large memory guests it has been observed that creating a memslot
for a very large range can take noticeable amount of time.
Investigation showed that the time is spent walking the rmaps to update
existing sptes to remove write access or set/clear dirty bits to support
dirty logging. These rmap walks are unnecessary when creating or moving
a memslot. A newly created memslot will not have any existing mappings,
and the existing mappings of a moved memslot will have been invalidated
and flushed. Any mappings established once the new/moved memslot becomes
visible will be set using the properties of the new slot.

Signed-off-by: Anthony Yznaga <anthony.yznaga@oracle.com>
Message-Id: <1591128450-11977-3-git-send-email-anthony.yznaga@oracle.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

parent 5688fed6

arch/x86/kvm/x86.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -10242,7 +10242,7 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
		*
		* FIXME: const-ify all uses of struct kvm_memory_slot.
		*/
		if (change != KVM_MR_DELETE)
		if (change == KVM_MR_FLAGS_ONLY)
		kvm_mmu_slot_apply_flags(kvm, (struct kvm_memory_slot *) new);

		/* Free the arrays associated with the old memslot. */

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