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Date:   Thu, 04 Feb 2021 21:49:12 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     x86@...nel.org, Josh Poimboeuf <jpoimboe@...hat.com>,
        Kees Cook <keescook@...omium.org>
Subject: [patch 09/12] x86/softirq: Remove indirection in do_softirq_own_stack()

Use the new inline stack switching and remove the old ASM indirect call
implementation.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
 arch/x86/entry/entry_64.S        |   39 -----------------------------
 arch/x86/include/asm/irq_stack.h |   52 ++++++++++++---------------------------
 arch/x86/kernel/irq_64.c         |    2 -
 3 files changed, 17 insertions(+), 76 deletions(-)

--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -756,45 +756,6 @@ SYM_CODE_START_LOCAL_NOALIGN(.Lbad_gs)
 SYM_CODE_END(.Lbad_gs)
 	.previous
 
-/*
- * rdi: New stack pointer points to the top word of the stack
- * rsi: Function pointer
- * rdx: Function argument (can be NULL if none)
- */
-SYM_FUNC_START(asm_call_on_stack)
-	/*
-	 * Save the frame pointer unconditionally. This allows the ORC
-	 * unwinder to handle the stack switch.
-	 */
-	pushq		%rbp
-	mov		%rsp, %rbp
-
-	/*
-	 * The unwinder relies on the word at the top of the new stack
-	 * page linking back to the previous RSP.
-	 */
-	mov		%rsp, (%rdi)
-	mov		%rdi, %rsp
-	/* Move the argument to the right place */
-	mov		%rdx, %rdi
-
-1:
-	.pushsection .discard.instr_begin
-	.long 1b - .
-	.popsection
-
-	CALL_NOSPEC	rsi
-
-2:
-	.pushsection .discard.instr_end
-	.long 2b - .
-	.popsection
-
-	/* Restore the previous stack pointer from RBP. */
-	leaveq
-	ret
-SYM_FUNC_END(asm_call_on_stack)
-
 #ifdef CONFIG_XEN_PV
 /*
  * A note on the "critical region" in our callback handler.
--- a/arch/x86/include/asm/irq_stack.h
+++ b/arch/x86/include/asm/irq_stack.h
@@ -191,20 +191,23 @@
 			      IRQ_CONSTRAINTS, regs, vector);		\
 }
 
-static __always_inline bool irqstack_active(void)
-{
-	return __this_cpu_read(hardirq_stack_inuse);
-}
-
-void asm_call_on_stack(void *sp, void (*func)(void), void *arg);
+#define ASM_CALL_SOFTIRQ						\
+	"call %P[__func]				\n"
 
-static __always_inline void __run_on_irqstack(void (*func)(void))
-{
-	void *tos = __this_cpu_read(hardirq_stack_ptr);
-
-	__this_cpu_write(hardirq_stack_inuse, true);
-	asm_call_on_stack(tos, func, NULL);
-	__this_cpu_write(hardirq_stack_inuse, false);
+/*
+ * Macro to invoke __do_softirq on the irq stack. Contrary to the above
+ * the only check which is necessary is whether the interrupt stack is
+ * in use already.
+ */
+#define run_softirq_on_irqstack_cond()					\
+{									\
+	if (__this_cpu_read(hardirq_stack_inuse)) {			\
+		__do_softirq();						\
+	} else {							\
+		__this_cpu_write(hardirq_stack_inuse, true);		\
+		__call_on_irqstack(__do_softirq, ASM_CALL_SOFTIRQ);	\
+		__this_cpu_write(hardirq_stack_inuse, false);		\
+	}								\
 }
 
 #else /* CONFIG_X86_64 */
@@ -225,29 +228,6 @@ static __always_inline void __run_on_irq
 	irq_exit_rcu();							\
 }
 
-static inline bool irqstack_active(void) { return false; }
-static inline void __run_on_irqstack(void (*func)(void)) { }
 #endif /* !CONFIG_X86_64 */
 
-static __always_inline bool irq_needs_irq_stack(struct pt_regs *regs)
-{
-	if (IS_ENABLED(CONFIG_X86_32))
-		return false;
-	if (!regs)
-		return !irqstack_active();
-	return !user_mode(regs) && !irqstack_active();
-}
-
-
-static __always_inline void run_on_irqstack_cond(void (*func)(void),
-						 struct pt_regs *regs)
-{
-	lockdep_assert_irqs_disabled();
-
-	if (irq_needs_irq_stack(regs))
-		__run_on_irqstack(func);
-	else
-		func();
-}
-
 #endif
--- a/arch/x86/kernel/irq_64.c
+++ b/arch/x86/kernel/irq_64.c
@@ -76,5 +76,5 @@ int irq_init_percpu_irqstack(unsigned in
 
 void do_softirq_own_stack(void)
 {
-	run_on_irqstack_cond(__do_softirq, NULL);
+	run_softirq_on_irqstack_cond();
 }

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