[PATCH v2 05/19] arm64: entry: move preempt logic to C

Mark Rutland
2021-05-19T13:08:40Z

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@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: James Morse <james.morse@arm.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Will Deacon <will@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 1fe60578e556..dbe0bb09fe86 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