[patch 09/12] x86/softirq: Remove indirection in do_softirq_own_stack()

Thomas Gleixner
2021-02-05T01:00:11Z

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

Signed-off-by: Thomas Gleixner <tglx@linutronix.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();
}