arm64: Skip preemption when exiting an NMI

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: Will Deacon <will.deacon@arm.com>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 02f809a..35ed484 100644 (file)
--- 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      preempt_schedule_irq            // irq en/disable is done inside
 1:
 #endif