[PATCH 2/7] KVM: arm64: Move OUTSIDE_GUEST_MODE publication past context being saved

[Marc Zyngier]

OUTSIDE_GUEST_MODE indicates to the rest of KVM that the vcpu has
exited. So far, this is set as soon as we return from the notional
hypervisor (which with VHE is just a function call away).

However, code that uses OUTSIDE_GUEST_MODE as a synchronisation point
relies on the vcpu state to have been written back to the in-memory
structures. Clearly, this is not what is happening

Move the publication of OUTSIDE_GUEST_MODE to the point where the state
is actually written, and give this write release semantics to ensure the
correct ordering.

Signed-off-by: Marc Zyngier <maz at kernel.org>
Cc: stable at vger.kernel.org
---
 arch/arm64/kvm/arm.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 73706464d2653..8b46fafdd3494 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -1334,13 +1334,13 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
 		smp_store_mb(vcpu->mode, IN_GUEST_MODE);
 
 		if (ret <= 0 || kvm_vcpu_exit_request(vcpu, &ret)) {
-			vcpu->mode = OUTSIDE_GUEST_MODE;
 			isb(); /* Ensure work in x_flush_hwstate is committed */
 			if (kvm_vcpu_has_pmu(vcpu))
 				kvm_pmu_sync_hwstate(vcpu);
 			if (unlikely(!irqchip_in_kernel(vcpu->kvm)))
 				kvm_timer_sync_user(vcpu);
 			kvm_vgic_sync_hwstate(vcpu);
+			smp_store_release(&vcpu->mode, OUTSIDE_GUEST_MODE);
 			local_irq_enable();
 			preempt_enable();
 			continue;
@@ -1356,7 +1356,6 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
 
 		ret = kvm_arm_vcpu_enter_exit(vcpu);
 
-		vcpu->mode = OUTSIDE_GUEST_MODE;
 		vcpu->stat.exits++;
 		/*
 		 * Back from guest
@@ -1390,6 +1389,12 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
 
 		kvm_arch_vcpu_ctxsync_fp(vcpu);
 
+		/*
+		 * All the state has been synchronised, let advertise
+		 * we're outside of the guest.
+		 */
+		smp_store_release(&vcpu->mode, OUTSIDE_GUEST_MODE);
+
 		/*
 		 * We must ensure that any pending interrupts are taken before
 		 * we exit guest timing so that timer ticks are accounted as
-- 
2.47.3