x86: Tell about irq stack coverage
x86-64 runs irq_exit() under the irq stack. So it can afford
to run softirqs in hardirq exit without the need to switch
the stacks. The hardirq stack is good enough for that.
Now x86-64 runs softirqs in the hardirq stack anyway, so what we
mostly skip is some needless per cpu refcounting updates there.
x86-32 is not concerned because it only runs the irq handler on
the irq stack.
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@au1.ibm.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul Mackerras <paulus@au1.ibm.com>
Cc: James Hogan <james.hogan@imgtec.com>
Cc: James E.J. Bottomley <jejb@parisc-linux.org>
Cc: Helge Deller <deller@gmx.de>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Andrew Morton <akpm@linux-foundation.org>
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index ee2fb9d..99eb1cc 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -123,6 +123,7 @@
select COMPAT_OLD_SIGACTION if IA32_EMULATION
select RTC_LIB
select HAVE_DEBUG_STACKOVERFLOW
+ select HAVE_IRQ_EXIT_ON_IRQ_STACK if X86_64
config INSTRUCTION_DECODER
def_bool y