From c0093f1a38a0fd6c32a2269f0533bb13fb95143d Mon Sep 17 00:00:00 2001
From: Paul Mackerras <paulus@ozlabs.org>
Date: Mon, 20 Nov 2017 16:12:25 +1100
Subject: [PATCH] KVM: PPC: Book3S HV: Fix conditions for starting vcpu

References: bsc#1061840
Patch-mainline: v4.16-rc1
Git-commit: c0093f1a38a0fd6c32a2269f0533bb13fb95143d

This corrects the test that determines whether a vcpu that has just
become able to run in the guest (e.g. it has just finished handling
a hypercall or hypervisor page fault) and whose virtual core is
already running somewhere as a "piggybacked" vcore can start
immediately or not.  (A piggybacked vcore is one which is executing
along with another vcore as a result of dynamic micro-threading.)

Previously the test tried to lock the piggybacked vcore using
spin_trylock, which would always fail because the vcore was already
locked, and so the vcpu would have to wait until its vcore exited
the guest before it could enter.

In fact the vcpu can enter if its vcore is in VCORE_PIGGYBACK state
and not already exiting (or exited) the guest, so the test in
VCORE_PIGGYBACK state is basically the same as for VCORE_RUNNING
state.

Coverity detected this as a double unlock issue, which it isn't
because the spin_trylock would always fail.  This will fix the
apparent double unlock as well.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
Acked-by: Michal Suchanek <msuchanek@suse.de>
---
 arch/powerpc/kvm/book3s_hv.c | 13 ++-----------
 1 file changed, 2 insertions(+), 11 deletions(-)

diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 597498d6db2e..c4f0bebfc5ba 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -3175,17 +3175,8 @@ static int kvmppc_run_vcpu(struct kvm_run *kvm_run, struct kvm_vcpu *vcpu)
 	 * this thread straight away and have it join in.
 	 */
 	if (!signal_pending(current)) {
-		if (vc->vcore_state == VCORE_PIGGYBACK) {
-			if (spin_trylock(&vc->lock)) {
-				if (vc->vcore_state == VCORE_RUNNING &&
-				    !VCORE_IS_EXITING(vc)) {
-					kvmppc_create_dtl_entry(vcpu, vc);
-					kvmppc_start_thread(vcpu, vc);
-					trace_kvm_guest_enter(vcpu);
-				}
-				spin_unlock(&vc->lock);
-			}
-		} else if (vc->vcore_state == VCORE_RUNNING &&
+		if ((vc->vcore_state == VCORE_PIGGYBACK ||
+		     vc->vcore_state == VCORE_RUNNING) &&
 			   !VCORE_IS_EXITING(vc)) {
 			kvmppc_create_dtl_entry(vcpu, vc);
 			kvmppc_start_thread(vcpu, vc);
-- 
2.13.7