arm64: entry: move NMI preempt logic to C

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@arm.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Joey Gouly <joey.gouly@arm.com>
Cc: James Morse <james.morse@arm.com>
Cc: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20210607094624.34689-6-mark.rutland@arm.com
Signed-off-by: Will Deacon <will@kernel.org>

diff --git a/arch/arm64/kernel/entry-common.c b/arch/arm64/kernel/entry-common.c
index 1fe6057..08d17eb 100644 (file)
--- a/arch/arm64/kernel/entry-common.c
+++ b/arch/arm64/kernel/entry-common.c
@@ -121,6 +121,15 @@ 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

diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 656f312..4496282 100644 (file)
--- 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