[PATCH v4 09/10] arm64: irqchip/gic-v3: Simplify NMI handling in IRQs disabled context

[Liao Chang]

After the recent refactoring to the exception entry code, the value of
PMR is not set to GIC_PRIO_IRQ_ON | GIC_PRIO_IRQ_I_SET unconditionally.
If kernel traps from IRQs disabled context, the PMR happens to
GIC_PRIO_IRQ_OFF, which allow only PESUDO_NMI could be acknowledged.
This patch leverage this fact to remove the unnecessary dropping of PMR
in NMI handler.

Signed-off-by: Liao Chang <liaochang1@xxxxxxxxxx>
---
 arch/arm64/kernel/entry-common.c |  4 ++--
 drivers/irqchip/irq-gic-v3.c     | 23 +----------------------
 2 files changed, 3 insertions(+), 24 deletions(-)

diff --git a/arch/arm64/kernel/entry-common.c b/arch/arm64/kernel/entry-common.c
index eabfc80df6fb..fb3f5b772f57 100644
--- a/arch/arm64/kernel/entry-common.c
+++ b/arch/arm64/kernel/entry-common.c
@@ -531,6 +531,8 @@ static __always_inline void __el1_pnmi(struct pt_regs *regs,
 static __always_inline void __el1_irq(struct pt_regs *regs,
 				      void (*handler)(struct pt_regs *))
 {
+	local_nmi_disable();
+
 	enter_from_kernel_mode(regs);
 
 	irq_enter_rcu();
@@ -544,8 +546,6 @@ static __always_inline void __el1_irq(struct pt_regs *regs,
 static void noinstr el1_interrupt(struct pt_regs *regs,
 				  void (*handler)(struct pt_regs *))
 {
-	local_nmi_disable();
-
 	if (IS_ENABLED(CONFIG_ARM64_PSEUDO_NMI) && !interrupts_enabled(regs))
 		__el1_pnmi(regs, handler);
 	else
diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
index ed7d8d87768f..de869051039b 100644
--- a/drivers/irqchip/irq-gic-v3.c
+++ b/drivers/irqchip/irq-gic-v3.c
@@ -831,28 +831,7 @@ static void __gic_handle_irq_from_irqson(struct pt_regs *regs)
  */
 static void __gic_handle_irq_from_irqsoff(struct pt_regs *regs)
 {
-	u64 pmr;
-	u32 irqnr;
-
-	/*
-	 * We were in a context with IRQs disabled. However, the
-	 * entry code has set PMR to a value that allows any
-	 * interrupt to be acknowledged, and not just NMIs. This can
-	 * lead to surprising effects if the NMI has been retired in
-	 * the meantime, and that there is an IRQ pending. The IRQ
-	 * would then be taken in NMI context, something that nobody
-	 * wants to debug twice.
-	 *
-	 * Until we sort this, drop PMR again to a level that will
-	 * actually only allow NMIs before reading IAR, and then
-	 * restore it to what it was.
-	 */
-	pmr = gic_read_pmr();
-	gic_pmr_mask_irqs();
-	isb();
-	irqnr = gic_read_iar();
-	gic_write_pmr(pmr);
-
+	u32 irqnr = gic_read_iar();
 	__gic_handle_nmi(irqnr, regs);
 }
 
-- 
2.34.1