[PATCH v4 05/20] arm64: entry: move NMI preempt logic to C

[Mark Rutland]

Currently portions of our preempt logic are written in C while other
parts are written in assembly. Let's clean this up a little bit by
moving the NMI preempt checks to C. For now, the preempt count (and
need_resched) checking is left in assembly, and will be converted
with the body of the IRQ handler in subsequent patches.

Other than the increased lockdep coverage there should be no functional
change as a result of this patch.

Signed-off-by: Mark Rutland <mark.rutland at arm.com>
Acked-by: Catalin Marinas <catalin.marinas at arm.com>
Acked-by: Marc Zyngier <maz at kernel.org>
Reviewed-by: Joey Gouly <joey.gouly at arm.com>
Cc: James Morse <james.morse at arm.com>
Cc: Will Deacon <will at kernel.org>
---
 arch/arm64/kernel/entry-common.c |  9 +++++++++
 arch/arm64/kernel/entry.S        | 12 +-----------
 2 files changed, 10 insertions(+), 11 deletions(-)

diff --git a/arch/arm64/kernel/entry-common.c b/arch/arm64/kernel/entry-common.c
index 1fe60578e556..08d17eb0ce13 100644
--- a/arch/arm64/kernel/entry-common.c
+++ b/arch/arm64/kernel/entry-common.c
@@ -122,6 +122,15 @@ asmlinkage void __sched arm64_preempt_schedule_irq(void)
 	lockdep_assert_irqs_disabled();
 
 	/*
+	 * DAIF.DA are cleared at the start of IRQ/FIQ handling, and when GIC
+	 * priority masking is used the GIC irqchip driver will clear DAIF.IF
+	 * using gic_arch_enable_irqs() for normal IRQs. If anything is set in
+	 * DAIF we must have handled an NMI, so skip preemption.
+	 */
+	if (system_uses_irq_prio_masking() && read_sysreg(daif))
+		return;
+
+	/*
 	 * Preempting a task from an IRQ means we leave copies of PSTATE
 	 * on the stack. cpufeature's enable calls may modify PSTATE, but
 	 * resuming one of these preempted tasks would undo those changes.
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 656f3129bfef..449628290ce8 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -562,17 +562,7 @@ tsk	.req	x28		// current thread_info
 
 #ifdef CONFIG_PREEMPTION
 	ldr	x24, [tsk, #TSK_TI_PREEMPT]	// get preempt count
-alternative_if ARM64_HAS_IRQ_PRIO_MASKING
-	/*
-	 * DA were cleared at start of handling, and IF are cleared by
-	 * the GIC irqchip driver using gic_arch_enable_irqs() for
-	 * normal IRQs. If anything is set, it means we come back from
-	 * an NMI instead of a normal IRQ, so skip preemption
-	 */
-	mrs	x0, daif
-	orr	x24, x24, x0
-alternative_else_nop_endif
-	cbnz	x24, 1f				// preempt count != 0 || NMI return path
+	cbnz	x24, 1f				// preempt count != 0
 	bl	arm64_preempt_schedule_irq	// irq en/disable is done inside
 1:
 #endif
-- 
2.11.0