linux-kernel - [RFC][PATCH 1/3] x86/entry: Collapse the 3 IRQ stack instances into a single macro

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Date:   Thu, 07 May 2020 18:10:21 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     tglx@...utronix.de
Cc:     jpoimboe@...hat.com, x86@...nel.org, linux-kernel@...r.kernel.org,
        luto@...nel.org, peterz@...radead.org
Subject: [RFC][PATCH 1/3] x86/entry: Collapse the 3 IRQ stack instances into a single macro

Because 1 copy of this magic is plenty.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
--- a/arch/x86/include/asm/irq_stack.h
+++ b/arch/x86/include/asm/irq_stack.h
@@ -12,10 +12,8 @@ static __always_inline bool irqstack_act
 	return __this_cpu_read(irq_count) != -1;
 }
 
-/*
- * Macro to emit code for running @func on the irq stack.
- */
-#define RUN_ON_IRQSTACK(func)	{					\
+#define __RUN_ON_IRQSTACK(_asm, ...)					\
+do {									\
 	unsigned long tos;						\
 									\
 	lockdep_assert_irqs_disabled();					\
@@ -30,45 +28,27 @@ static __always_inline bool irqstack_act
 		"	.pushsection .discard.instr_begin	\n"	\
 		"	.long 1b - .				\n"	\
 		"	.popsection				\n"	\
-		"call	" __ASM_FORM(func) "			\n"	\
+		_asm "                                          \n"	\
 		"2:						\n"	\
 		"	.pushsection .discard.instr_end		\n"	\
 		"	.long 2b - .				\n"	\
 		"	.popsection				\n"	\
 		"popq	%%rsp					\n"	\
 		:							\
-		: [ts] "r" (tos)					\
+		: [ts] "r" (tos), ##__VA_ARGS__				\
 		: "memory"						\
 		);							\
 	__this_cpu_sub(irq_count, 1);					\
-}
+} while (0)
 
-#define RUN_ON_IRQSTACK_ARG1(func, arg) {				\
-	unsigned long tos;						\
-									\
-	tos = ((unsigned long)__this_cpu_read(hardirq_stack_ptr)) - 8;	\
-									\
-	__this_cpu_add(irq_count, 1);					\
-	asm volatile(							\
-		"movq	%%rsp, (%[ts])				\n"	\
-		"movq	%[ts], %%rsp				\n"	\
-		"1:						\n"	\
-		"	.pushsection .discard.instr_begin	\n"	\
-		"	.long 1b - .				\n"	\
-		"	.popsection				\n"	\
-		"call	" __ASM_FORM(func) "			\n"	\
-		"2:						\n"	\
-		"	.pushsection .discard.instr_end		\n"	\
-		"	.long 2b - .				\n"	\
-		"	.popsection				\n"	\
-		"popq	%%rsp					\n"	\
-		:							\
-		: [ts] "r" (tos),					\
-		  "D" (arg)						\
-		: "memory"						\
-		);							\
-	__this_cpu_sub(irq_count, 1);					\
-}
+/*
+ * Macro to emit code for running @func on the irq stack.
+ */
+#define RUN_ON_IRQSTACK(func) \
+	__RUN_ON_IRQSTACK("call" __ASM_FORM(func))
+
+#define RUN_ON_IRQSTACK_ARG1(func, arg) \
+	__RUN_ON_IRQSTACK("call" __ASM_FORM(func), "D" (arg))
 
 #else /* CONFIG_X86_64 */
 static __always_inline bool irqstack_active(void) { return false; }
--- a/arch/x86/kernel/irq_64.c
+++ b/arch/x86/kernel/irq_64.c
@@ -74,35 +74,7 @@ int irq_init_percpu_irqstack(unsigned in
 
 static noinstr void handle_irq_on_irqstack(struct irq_desc *desc)
 {
-	unsigned long tos;
-
-	tos = (unsigned long) __this_cpu_read(hardirq_stack_ptr) - 8;
-
-	__this_cpu_add(irq_count, 1);
-	/*
-	 * The unwinder requires that the top of the IRQ stack links back
-	 * to the previous stack and RBP is set up.
-	 */
-	asm volatile(
-		"movq	%%rsp, (%[ts])				\n"
-		"movq	%[ts], %%rsp				\n"
-		"1:						\n"
-		"	.pushsection .discard.instr_begin	\n"
-		"	.long 1b - .				\n"
-		"	.popsection				\n"
-		CALL_NOSPEC
-		"2:						\n"
-		"	.pushsection .discard.instr_end		\n"
-		"	.long 2b - .				\n"
-		"	.popsection				\n"
-		"popq	%%rsp					\n"
-		:
-		: [ts] "r" (tos),
-		  [thunk_target] "r" (desc->handle_irq),
-		  "D" (desc)
-		: "memory"
-		);
-	__this_cpu_sub(irq_count, 1);
+	__RUN_ON_IRQSTACK(CALL_NOSPEC, THUNK_TARGET(desc->handle_irq), "D" (desc));
 }
 
 void handle_irq(struct irq_desc *desc, struct pt_regs *regs)