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Subject[PATCH v10 23/25] arm64: Skip preemption when exiting an NMI
Date
Handling of an NMI should not set any TIF flags. For NMIs received from
EL0 the current exit path is safe to use.

However, an NMI received at EL1 could have interrupted some task context
that has set the TIF_NEED_RESCHED flag. Preempting a task should not
happen as a result of an NMI.

Skip preemption after handling an NMI from EL1.

Signed-off-by: Julien Thierry <julien.thierry@arm.com>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Marc Zyngier <marc.zyngier@arm.com>
---
arch/arm64/kernel/entry.S | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 35a47f6..acf1250 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -624,7 +624,15 @@ el1_irq:

#ifdef CONFIG_PREEMPT
ldr x24, [tsk, #TSK_TI_PREEMPT] // get preempt count
- cbnz x24, 1f // preempt count != 0
+alternative_if ARM64_HAS_IRQ_PRIO_MASKING
+ /*
+ * DA_F were cleared at start of handling. If anything is set in DAIF,
+ * we come back from an NMI, so skip preemption
+ */
+ mrs x0, daif
+ orr x24, x24, x0
+alternative_else_nop_endif
+ cbnz x24, 1f // preempt count != 0 || NMI return path
bl el1_preempt
1:
#endif
--
1.9.1
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