[PATCH v3 4/7] powerpc/64s: Fix irq state management in runlatch functions

From: Nicholas Piggin <npiggin@gmail.com>
To: linuxppc-dev@lists.ozlabs.org
Cc: Nicholas Piggin <npiggin@gmail.com>
Subject: [PATCH v3 4/7] powerpc/64s: Fix irq state management in runlatch functions
Date: Mon, 26 Sep 2022 15:43:02 +1000	[thread overview]
Message-ID: <20220926054305.2671436-5-npiggin@gmail.com> (raw)
In-Reply-To: <20220926054305.2671436-1-npiggin@gmail.com>

When irqs are soft-disabled, MSR[EE] is volatile and can change from
1 to 0 asynchronously (if a PACA_IRQ_MUST_HARD_MASK interrupt hits).
So it can not be used to check hard IRQ enabled status, except to
confirm it is disabled.

ppc64_runlatch_on/off functions use MSR this way to decide whether to
re-enable MSR[EE] after disabling it, which leads to MSR[EE] being
enabled when it shouldn't be (when a PACA_IRQ_MUST_HARD_MASK had
disabled it between reading the MSR and clearing EE).

This has been tolerated in the kernel previously, and it doesn't seem
to cause a problem, but it is unexpected and may trip warnings or cause
other problems as we tighten up this state management. Fix this by only
re-enabling if PACA_IRQ_HARD_DIS is clear.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
 arch/powerpc/include/asm/runlatch.h | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/arch/powerpc/include/asm/runlatch.h b/arch/powerpc/include/asm/runlatch.h
index cfb390edf7d0..ceb66d761fe1 100644
--- a/arch/powerpc/include/asm/runlatch.h
+++ b/arch/powerpc/include/asm/runlatch.h
@@ -19,10 +19,9 @@ extern void __ppc64_runlatch_off(void);
 	do {							\
 		if (cpu_has_feature(CPU_FTR_CTRL) &&		\
 		    test_thread_local_flags(_TLF_RUNLATCH)) {	\
-			unsigned long msr = mfmsr();		\
 			__hard_irq_disable();			\
 			__ppc64_runlatch_off();			\
-			if (msr & MSR_EE)			\
+			if (!(local_paca->irq_happened & PACA_IRQ_HARD_DIS)) \
 				__hard_irq_enable();		\
 		}      						\
 	} while (0)
@@ -31,10 +30,9 @@ extern void __ppc64_runlatch_off(void);
 	do {							\
 		if (cpu_has_feature(CPU_FTR_CTRL) &&		\
 		    !test_thread_local_flags(_TLF_RUNLATCH)) {	\
-			unsigned long msr = mfmsr();		\
 			__hard_irq_disable();			\
 			__ppc64_runlatch_on();			\
-			if (msr & MSR_EE)			\
+			if (!(local_paca->irq_happened & PACA_IRQ_HARD_DIS)) \
 				__hard_irq_enable();		\
 		}      						\
 	} while (0)
-- 
2.37.2

