linux-kernel - [PATCH] KVM: SVM: unconditionally wake up VCPU on IOMMU interrupt

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Date:   Tue, 10 Oct 2017 12:57:29 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     suravee.suthikulpanit@....com, rkrcmar@...hat.com
Subject: [PATCH] KVM: SVM: unconditionally wake up VCPU on IOMMU interrupt

Checking the mode is unnecessary, and is done without a memory barrier
separating the LAPIC write from the vcpu->mode read; in addition,
kvm_vcpu_wake_up is already doing a check for waiters on the wait queue
that has the same effect.

In practice it's safe because spin_lock has full-barrier semantics on x86,
but don't be too clever.

Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
 arch/x86/kvm/svm.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 01e6e8fab5d6..712406f725a2 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1034,15 +1034,12 @@ static int avic_ga_log_notifier(u32 ga_tag)
 	}
 	spin_unlock_irqrestore(&svm_vm_data_hash_lock, flags);
 
-	if (!vcpu)
-		return 0;
-
 	/* Note:
 	 * At this point, the IOMMU should have already set the pending
 	 * bit in the vAPIC backing page. So, we just need to schedule
 	 * in the vcpu.
 	 */
-	if (vcpu->mode == OUTSIDE_GUEST_MODE)
+	if (vcpu)
 		kvm_vcpu_wake_up(vcpu);
 
 	return 0;
-- 
1.8.3.1