[PATCH 12/43] KVM: arm64: gic-v5: Clear db_fired flag before making VPE non-resident

[Sascha Bischoff]

The GICv5 VPE doorbells are used to notify KVM that a non-resident VPE
has an interrupt to handle. We use the db_fired flag to track this,
and therefore need to ensure that the flag is cleared once it has been
consumed.

Explicitly set the db_fired flag to false before making a VPE
non-resident as any state is stale at this stage. This also ensures
that any incoming doorbells, if requested, will be observed.

Signed-off-by: Sascha Bischoff <sascha.bischoff at arm.com>
---
 arch/arm64/kvm/hyp/vgic-v5-sr.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/arm64/kvm/hyp/vgic-v5-sr.c b/arch/arm64/kvm/hyp/vgic-v5-sr.c
index 04c5846b9abac..d27fe2911df3f 100644
--- a/arch/arm64/kvm/hyp/vgic-v5-sr.c
+++ b/arch/arm64/kvm/hyp/vgic-v5-sr.c
@@ -22,6 +22,15 @@ void __vgic_v5_make_resident(struct vgic_v5_cpu_if *cpu_if)
 
 void __vgic_v5_make_non_resident(struct vgic_v5_cpu_if *cpu_if)
 {
+	/*
+	 * Clear the db_fired state to ensure that we're ready for the next
+	 * doorbell when it is requested. If a doorbell firing caused us to
+	 * enter the guest, then we've already consumed that state at this
+	 * point, so this is safe to clear. Use WRITE_ONCE() to ensure we're not
+	 * racing with the doorbell firing and setting the state true again.
+	 */
+	WRITE_ONCE(cpu_if->gicv5_vpe.db_fired, false);
+
 	/*
 	 * Make as non-resident before actually making non-resident. Avoids race
 	 * with doorbell arriving.
-- 
2.34.1