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From: Anthony Yznaga <anthony.yznaga@oracle.com>
To: kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Cc: pbonzini@redhat.com, sean.j.christopherson@intel.com,
	vkuznets@redhat.com, wanpengli@tencent.com, jmattson@google.com,
	joro@8bytes.org, tglx@linutronix.de, mingo@redhat.com,
	bp@alien8.de, x86@kernel.org, hpa@zytor.com,
	steven.sistare@oracle.com, anthony.yznaga@oracle.com
Subject: [PATCH 2/3] KVM: x86: avoid unnecessary rmap walks when creating/moving slots
Date: Tue,  2 Jun 2020 13:07:29 -0700	[thread overview]
Message-ID: <1591128450-11977-3-git-send-email-anthony.yznaga@oracle.com> (raw)
In-Reply-To: <1591128450-11977-1-git-send-email-anthony.yznaga@oracle.com>

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>
---
 arch/x86/kvm/x86.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 23fd888e52ee..d211c8ced6bb 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -10138,7 +10138,7 @@ 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. */
-- 
2.13.3


  parent reply	other threads:[~2020-06-02 20:09 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-02 20:07 [PATCH 0/3] avoid unnecessary memslot rmap walks Anthony Yznaga
2020-06-02 20:07 ` [PATCH 1/3] KVM: x86: remove unnecessary rmap walk of read-only memslots Anthony Yznaga
2020-06-02 20:07 ` Anthony Yznaga [this message]
2020-06-02 20:07 ` [PATCH 3/3] KVM: x86: minor code refactor and comments fixup around dirty logging Anthony Yznaga
2020-06-04 18:42 ` [PATCH 0/3] avoid unnecessary memslot rmap walks Paolo Bonzini

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