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x86/irq: Sanitize irq stack tracking

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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 <tglx@linutronix.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20210210002512.228830141@linutronix.de
This commit is contained in:
Thomas Gleixner
2021-02-10 00:40:43 +01:00
parent 15f720aabe
commit e7f8900179
4 changed files with 10 additions and 10 deletions
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2
arch/x86/include/asm/processor.h
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@@ -454,7 +454,7 @@ static inline unsigned long cpu_kernelmode_gs_base(int cpu)
return (unsigned long)per_cpu(fixed_percpu_data.gs_base, cpu);
}
DECLARE_PER_CPU(unsigned int, irq_count);
DECLARE_PER_CPU(bool, hardirq_stack_inuse);
extern asmlinkage void ignore_sysret(void);
/* Save actual FS/GS selectors and bases to current->thread */