[RFC 10/12] riscv: Enable NMIs during interrupt handling

[Xu Lu]

Hardware automatically clearing SIE field of CSR_STATUS whenever
thread traps into kernel by interrupt, disabling all irqs including NMIs
during interrupt handling.

This commit re-enable NMIs during interrupt handling by setting the SIE
field in CSR_STATUS and restoring NMIs bits in CSR_IE. Normal interrupts
are still disabled during interrupt handling and NMIs are also disabled
during NMIs handling to avoid nesting.

Signed-off-by: Xu Lu <luxu.kernel at bytedance.com>
Signed-off-by: Hangjing Li <lihangjing at bytedance.com>
Reviewed-by: Liang Deng <dengliang.1214 at bytedance.com>
Reviewed-by: Yu Li <liyu.yukiteru at bytedance.com>
---
 arch/riscv/kernel/traps.c        | 44 +++++++++++++++++++++++---------
 drivers/irqchip/irq-riscv-intc.c |  2 ++
 2 files changed, 34 insertions(+), 12 deletions(-)

diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
index 63d3c1417563..185743edfa09 100644
--- a/arch/riscv/kernel/traps.c
+++ b/arch/riscv/kernel/traps.c
@@ -356,20 +356,11 @@ asmlinkage __visible noinstr void do_page_fault(struct pt_regs *regs)
 }
 #endif
 
-static void noinstr handle_riscv_irq(struct pt_regs *regs)
+static void noinstr do_interrupt(struct pt_regs *regs)
 {
 	struct pt_regs *old_regs;
 
-	irq_enter_rcu();
 	old_regs = set_irq_regs(regs);
-	handle_arch_irq(regs);
-	set_irq_regs(old_regs);
-	irq_exit_rcu();
-}
-
-asmlinkage void noinstr do_irq(struct pt_regs *regs)
-{
-	irqentry_state_t state = irqentry_enter(regs);
 #ifdef CONFIG_IRQ_STACKS
 	if (on_thread_stack()) {
 		ulong *sp = per_cpu(irq_stack_ptr, smp_processor_id())
@@ -382,7 +373,9 @@ asmlinkage void noinstr do_irq(struct pt_regs *regs)
 		"addi	s0, sp, 2*"RISCV_SZPTR "\n"
 		"move	sp, %[sp]		\n"
 		"move	a0, %[regs]		\n"
-		"call	handle_riscv_irq	\n"
+		"la	t0, handle_arch_irq	\n"
+		REG_L"	t1, (t0)		\n"
+		"jalr	t1			\n"
 		"addi	sp, s0, -2*"RISCV_SZPTR"\n"
 		REG_L"  s0, (sp)		\n"
 		"addi	sp, sp, "RISCV_SZPTR   "\n"
@@ -398,11 +391,38 @@ asmlinkage void noinstr do_irq(struct pt_regs *regs)
 		  "memory");
 	} else
 #endif
-		handle_riscv_irq(regs);
+		handle_arch_irq(regs);
+	set_irq_regs(old_regs);
+}
+
+static __always_inline void __do_nmi(struct pt_regs *regs)
+{
+	irqentry_state_t state = irqentry_nmi_enter(regs);
+
+	do_interrupt(regs);
+
+	irqentry_nmi_exit(regs, state);
+}
+
+static __always_inline void __do_irq(struct pt_regs *regs)
+{
+	irqentry_state_t state = irqentry_enter(regs);
+
+	irq_enter_rcu();
+	do_interrupt(regs);
+	irq_exit_rcu();
 
 	irqentry_exit(regs, state);
 }
 
+asmlinkage void noinstr do_irq(struct pt_regs *regs)
+{
+	if (IS_ENABLED(CONFIG_RISCV_PSEUDO_NMI) && regs_irqs_disabled(regs))
+		__do_nmi(regs);
+	else
+		__do_irq(regs);
+}
+
 #ifdef CONFIG_GENERIC_BUG
 int is_valid_bugaddr(unsigned long pc)
 {
diff --git a/drivers/irqchip/irq-riscv-intc.c b/drivers/irqchip/irq-riscv-intc.c
index c672c0c64d5d..80ed8606e04d 100644
--- a/drivers/irqchip/irq-riscv-intc.c
+++ b/drivers/irqchip/irq-riscv-intc.c
@@ -34,7 +34,9 @@ static asmlinkage void riscv_intc_irq(struct pt_regs *regs)
 		generic_handle_domain_nmi(intc_domain, cause);
 		nmi_exit();
 	} else {
+		enable_nmis();
 		generic_handle_domain_irq(intc_domain, cause);
+		disable_nmis();
 	}
 }
 
-- 
2.20.1