diff mbox series

[V2,7/8] kvm: x86/mmu: Reduce the update to the spte in FNAME(sync_page)

Message ID 20230207155735.2845-8-jiangshanlai@gmail.com (mailing list archive)
State New, archived
Headers show
Series [V2,1/8] kvm: x86/mmu: Use KVM_MMU_ROOT_XXX for kvm_mmu_invalidate_gva() | expand

Commit Message

Lai Jiangshan Feb. 7, 2023, 3:57 p.m. UTC 
From: Lai Jiangshan <jiangshan.ljs@antgroup.com>

Sometimes when the guest updates its pagetable, it adds only new gptes
to it without changing any existed one, so there is no point to update
the sptes for these existed gptes.

Also when the sptes for these unchanged gptes are updated, the AD
bits are also removed since make_spte() is called with prefetch=true
which might result unneeded TLB flushing.

Do nothing if the gpte's permissions are unchanged.

Signed-off-by: Lai Jiangshan <jiangshan.ljs@antgroup.com>
---
 arch/x86/kvm/mmu/paging_tmpl.h | 5 +++++
 1 file changed, 5 insertions(+)
diff mbox series

Patch

diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h
index 0031fe22af3d..fca5ce349d9d 100644
--- a/arch/x86/kvm/mmu/paging_tmpl.h
+++ b/arch/x86/kvm/mmu/paging_tmpl.h
@@ -967,6 +967,11 @@  static int FNAME(sync_spte)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp, int
 		drop_spte(vcpu->kvm, &sp->spt[i]);
 		return 1;
 	}
+	/*
+	 * Do nothing if the permissions are unchanged.
+	 */
+	if (kvm_mmu_page_get_access(sp, i) == pte_access)
+		return 0;
 
 	/* Update the shadowed access bits in case they changed. */
 	kvm_mmu_page_set_access(sp, i, pte_access);