[PATCH v7 23/25] arm64: Skip preemption when exiting an NMI

From: Julien Thierry
Date: Wed Dec 12 2018 - 11:49:02 EST

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@xxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Cc: Marc Zyngier <marc.zyngier@xxxxxxx>
arch/arm64/kernel/entry.S | 8 ++++++++
1 file changed, 8 insertions(+)

diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 2804c81..7c9555c 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -637,6 +637,14 @@ el1_irq:

ldr w24, [tsk, #TSK_TI_PREEMPT] // get preempt count
+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 w24, w24, w0
cbnz w24, 1f // preempt count != 0
ldr x0, [tsk, #TSK_TI_FLAGS] // get flags
tbz x0, #TIF_NEED_RESCHED, 1f // needs rescheduling?