[PATCH 2/2] KVM: PPC: Replay pending interrupts before entering the guest

[Shrikanth Hegde <sshegde@linux.ibm.com>]

After applying preempt disable patch, i.e PATCH 1/2, Christian reported
a subsequent warning stopping his board to boot properly.

WARNING: at .kvmppc_fix_ee_before_entry+0x10/0x28, CPU#0: qemu-system-ppc/4667
CPU: 0 UID: 1000 PID: 4667 Comm: qemu-system-ppc Tainted: G        W           7.3.0-rc4-2-powerpc64-smp #1 PREEMPT
Tainted: [W]=WARN
Hardware name: varisys,CYRUS5040 e5500 0x80240012 CoreNet Generic
NIP [c00000000005dc3c] .kvmppc_fix_ee_before_entry+0x10/0x28
LR [c00000000005f298] .kvmppc_handle_exit+0x5b4/0x5e8
Call Trace:
[c000000086587780] [c00000000005ee10] .kvmppc_handle_exit+0x12c/0x5e8 (unreliable)
[c000000086587830] [c000000000062068] .kvmppc_resume_host+0xb8/0x10c

It triggers below warning...

static inline void kvmppc_fix_ee_before_entry(void)
{
        trace_hardirqs_on();

        /*
         * To avoid races, the caller must have gone directly from having
         * interrupts fully-enabled to hard-disabled.
         */
        WARN_ON(local_paca->irq_happened != PACA_IRQ_HARD_DIS);

This happens since kvmppc_prepare_to_enter does first local_irq_disable
followed by hard_irq_disable. This leaves a small window where interrupt
may occur and it could set the irq pending bit in PACA. When that
happens replay that interrupt before entering the guest.

Fixes: 12013e3d4695 ("KVM: powerpc: Use generic xfer to guest work function")
Reported-by: Christian Zigotzky <chzigotzky@xenosoft.de>
Closes: https://lore.kernel.org/all/b8f82519-9ae5-c247-e020-e79c627e57df@xenosoft.de/
Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
---
 arch/powerpc/kvm/powerpc.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
index 9194cf492d1c..847ff07c364b 100644
--- a/arch/powerpc/kvm/powerpc.c
+++ b/arch/powerpc/kvm/powerpc.c
@@ -147,6 +147,19 @@ int kvmppc_prepare_to_enter(struct kvm_vcpu *vcpu)
 			continue;
 		}
 
+#ifdef CONFIG_PPC64
+		/*
+		 * Interrupt arrived between the soft and hard
+		 * disable. Replay it and retry guest entry.
+		 */
+		if (unlikely(local_paca->irq_happened != PACA_IRQ_HARD_DIS)) {
+			local_irq_enable();
+			local_irq_disable();
+			hard_irq_disable();
+			continue;
+		}
+#endif
+
 		guest_enter_irqoff();
 		return 1;
 	}
-- 
2.52.0