KVM: PPC: set IN_GUEST_MODE before checking requests
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>
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 @@
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 @@
#endif
kvm_guest_enter();
-
- /* Going into guest context! Yay! */
- vcpu->mode = IN_GUEST_MODE;
- smp_wmb();
-
break;
}