[PATCH 05/14] arm64: entry: move preempt logic to C

[Mark Rutland]

Currently portions of our preempt logic are written in C while other
parts are written in assembly. There's no reason any of this needs to
live in assembly, so let's move the rest of the lgoic to C. At the same
time, let's make the comment a bit clearer.

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>
Cc: Catalin Marinas <catalin.marinas at arm.com>
Cc: James Morse <james.morse at arm.com>
Cc: Marc Zyngier <maz at kernel.org>
Cc: Will Deacon <will at kernel.org>
---
 arch/arm64/kernel/entry-common.c | 12 ++++++++++++
 arch/arm64/kernel/entry.S        | 13 -------------
 2 files changed, 12 insertions(+), 13 deletions(-)

diff --git a/arch/arm64/kernel/entry-common.c b/arch/arm64/kernel/entry-common.c
index 33b3660beea3..87997a4a0936 100644
--- a/arch/arm64/kernel/entry-common.c
+++ b/arch/arm64/kernel/entry-common.c
@@ -121,6 +121,18 @@ asmlinkage void __sched arm64_preempt_schedule_irq(void)
 {
 	lockdep_assert_irqs_disabled();
 
+	if (preempt_count() != 0)
+		return;
+
+	/*
+	 * 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
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 656f3129bfef..8c7ddd651756 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -561,20 +561,7 @@ tsk	.req	x28		// current thread_info
 	irq_handler	\handler
 
 #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
 	bl	arm64_preempt_schedule_irq	// irq en/disable is done inside
-1:
 #endif
 
 	mov	x0, sp
-- 
2.11.0