From e7f89001797148e8dc7060c335df2c56e73a8c7a Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Wed, 10 Feb 2021 00:40:43 +0100 Subject: x86/irq: Sanitize irq stack tracking The recursion protection for hard interrupt stacks is an unsigned int per CPU variable initialized to -1 named __irq_count. The irq stack switching is only done when the variable is -1, which creates worse code than just checking for 0. When the stack switching happens it uses this_cpu_add/sub(1), but there is no reason to do so. It simply can use straight writes. This is a historical leftover from the low level ASM code which used inc and jz to make a decision. Rename it to hardirq_stack_inuse, make it a bool and use plain stores. Signed-off-by: Thomas Gleixner Reviewed-by: Kees Cook Link: https://lore.kernel.org/r/20210210002512.228830141@linutronix.de --- arch/x86/kernel/process_64.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'arch/x86/kernel/process_64.c') diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c index ad582f9ac5a6..d08307df69ad 100644 --- a/arch/x86/kernel/process_64.c +++ b/arch/x86/kernel/process_64.c @@ -539,7 +539,7 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p) int cpu = smp_processor_id(); WARN_ON_ONCE(IS_ENABLED(CONFIG_DEBUG_ENTRY) && - this_cpu_read(irq_count) != -1); + this_cpu_read(hardirq_stack_inuse)); if (!test_thread_flag(TIF_NEED_FPU_LOAD)) switch_fpu_prepare(prev_fpu, cpu); -- cgit v1.2.3