Patchwork [52/56] KVM: PPC: set IN_GUEST_MODE before checking requests

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Submitter Alexander Graf
Date Oct. 4, 2012, 1:37 p.m.
Message ID <1349357844-11288-53-git-send-email-agraf@suse.de>
Download mbox | patch
Permalink /patch/189146/
State New
Headers show

Comments

Alexander Graf - Oct. 4, 2012, 1:37 p.m.
From: Scott Wood <scottwood@freescale.com>

Avoid a race as described in the code comment.

Also remove a related smp_wmb() from booke's kvmppc_prepare_to_enter().
I can't see any reason for it, and the book3s_pr version doesn't have it.

Signed-off-by: Scott Wood <scottwood@freescale.com>
Signed-off-by: Alexander Graf <agraf@suse.de>
---
 arch/powerpc/kvm/booke.c   |    1 -
 arch/powerpc/kvm/powerpc.c |   14 +++++++++-----
 2 files changed, 9 insertions(+), 6 deletions(-)

Patch

diff --git a/arch/powerpc/kvm/booke.c b/arch/powerpc/kvm/booke.c
index 69d047c..3d1f35d 100644
--- a/arch/powerpc/kvm/booke.c
+++ b/arch/powerpc/kvm/booke.c
@@ -674,7 +674,6 @@  int kvmppc_vcpu_run(struct kvm_run *kvm_run, struct kvm_vcpu *vcpu)
 
 out:
 	vcpu->mode = OUTSIDE_GUEST_MODE;
-	smp_wmb();
 	return ret;
 }
 
diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
index 6002ea9..deb0d59 100644
--- a/arch/powerpc/kvm/powerpc.c
+++ b/arch/powerpc/kvm/powerpc.c
@@ -78,7 +78,16 @@  int kvmppc_prepare_to_enter(struct kvm_vcpu *vcpu)
 			break;
 		}
 
+		vcpu->mode = IN_GUEST_MODE;
+
+		/*
+		 * Reading vcpu->requests must happen after setting vcpu->mode,
+		 * so we don't miss a request because the requester sees
+		 * OUTSIDE_GUEST_MODE and assumes we'll be checking requests
+		 * before next entering the guest (and thus doesn't IPI).
+		 */
 		smp_mb();
+
 		if (vcpu->requests) {
 			/* Make sure we process requests preemptable */
 			local_irq_enable();
@@ -111,11 +120,6 @@  int kvmppc_prepare_to_enter(struct kvm_vcpu *vcpu)
 #endif
 
 		kvm_guest_enter();
-
-		/* Going into guest context! Yay! */
-		vcpu->mode = IN_GUEST_MODE;
-		smp_wmb();
-
 		break;
 	}