[PATCH v2 3/3] KVM: PPC: Use ppc_hard_irq_disable before guest entry

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

After applying preempt disable patch, i.e PATCH 2/3, 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.

That local_irq_disable was necessary for PPC32 to track the lockdep
state etc. On PPC64 hard_irq_disable is good enough. There is no need to
do both. Use the new irq api to do the necessary one.

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 | 14 +++-----------
 1 file changed, 3 insertions(+), 11 deletions(-)

diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
index 9194cf492d1c..4ee3d7bfe917 100644
--- a/arch/powerpc/kvm/powerpc.c
+++ b/arch/powerpc/kvm/powerpc.c
@@ -81,13 +81,7 @@ int kvmppc_prepare_to_enter(struct kvm_vcpu *vcpu)
 	int r;
 
 	WARN_ON(irqs_disabled());
-	/*
-	 * local_irq_disable() first: on 32-bit, hard_irq_disable() alone is a
-	 * raw MSR[EE] clear that bypasses the lockdep/irq-tracing state, and
-	 * the xfer_to_guest_mode helpers assert IRQs are seen as disabled.
-	 */
-	local_irq_disable();
-	hard_irq_disable();
+	ppc_hard_irq_disable();
 
 	while (true) {
 		xfer_to_guest_mode_prepare();
@@ -101,8 +95,7 @@ int kvmppc_prepare_to_enter(struct kvm_vcpu *vcpu)
 			 */
 			local_irq_enable();
 			r = kvm_xfer_to_guest_mode_handle_work(vcpu);
-			local_irq_disable();
-			hard_irq_disable();
+			ppc_hard_irq_disable();
 			if (r) {
 				/*
 				 * The generic helper does not set the exit
@@ -134,8 +127,7 @@ int kvmppc_prepare_to_enter(struct kvm_vcpu *vcpu)
 			local_irq_enable();
 			trace_kvm_check_requests(vcpu);
 			r = kvmppc_core_check_requests(vcpu);
-			local_irq_disable();
-			hard_irq_disable();
+			ppc_hard_irq_disable();
 			if (r > 0)
 				continue;
 			break;
-- 
2.52.0