linux-kernel - [PATCH 4/7] KVM/x86: Call smp_wmb() before increasing tlbs

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Date:	Sun, 13 Mar 2016 11:10:27 +0800
From:	Lan Tianyu <tianyu.lan@...el.com>
To:	gleb@...nel.org, pbonzini@...hat.com, tglx@...utronix.de,
	mingo@...hat.com, hpa@...or.com, x86@...nel.org,
	guangrong.xiao@...ux.intel.com
Cc:	Lan Tianyu <tianyu.lan@...el.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH 4/7] KVM/x86: Call smp_wmb() before increasing tlbs_dirty

Update spte before increasing tlbs_dirty to make sure no tlb flush
in lost after spte is zapped. This pairs with the barrier in the
kvm_flush_remote_tlbs().

Signed-off-by: Lan Tianyu <tianyu.lan@...el.com>
---
 arch/x86/kvm/paging_tmpl.h | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index e159a81..d34475e 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -949,6 +949,12 @@ static int FNAME(sync_page)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp)
 			return 0;
 
 		if (FNAME(prefetch_invalid_gpte)(vcpu, sp, &sp->spt[i], gpte)) {
+			/*
+			 * Update spte before increasing tlbs_dirty to make sure
+			 * no tlb flush in lost after spte is zapped, see the
+			 * comments in kvm_flush_remote_tlbs().
+			 */
+			smp_wmb();
 			vcpu->kvm->tlbs_dirty++;
 			continue;
 		}
@@ -964,6 +970,11 @@ static int FNAME(sync_page)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp)
 
 		if (gfn != sp->gfns[i]) {
 			drop_spte(vcpu->kvm, &sp->spt[i]);
+			/*
+			 * The same as above where we are doing
+			 * prefetch_invalid_gpte().
+			 */
+			smp_wmb();
 			vcpu->kvm->tlbs_dirty++;
 			continue;
 		}
-- 
1.8.4.rc0.1.g8f6a3e5.dirty