From a97439aa1aec10387797b4abae3cf117de1c90d7 Mon Sep 17 00:00:00 2001 From: Andy Lutomirski Date: Wed, 15 Jul 2015 10:29:41 -0700 Subject: [PATCH] x86/entry/64, x86/nmi/64: Add CONFIG_DEBUG_ENTRY NMI testing code It turns out to be rather tedious to test the NMI nesting code. Make it easier: add a new CONFIG_DEBUG_ENTRY option that causes the NMI handler to pre-emptively unmask NMIs. With this option set, errors in the repeat_nmi logic or failures to detect that we're in a nested NMI will result in quick panics under perf (especially if multiple counters are running at high frequency) instead of requiring an unusual workload that generates page faults or breakpoints inside NMIs. I called it CONFIG_DEBUG_ENTRY instead of CONFIG_DEBUG_NMI_ENTRY because I want to add new non-NMI checks elsewhere in the entry code in the future, and I'd rather not add too many new config options or add this option and then immediately rename it. Signed-off-by: Andy Lutomirski Reviewed-by: Steven Rostedt Cc: Borislav Petkov Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Signed-off-by: Ingo Molnar --- arch/x86/Kconfig.debug | 12 ++++++++++++ arch/x86/entry/entry_64.S | 15 +++++++++++++++ 2 files changed, 27 insertions(+) diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug index a15893d17c55..d8c0d3266173 100644 --- a/arch/x86/Kconfig.debug +++ b/arch/x86/Kconfig.debug @@ -297,6 +297,18 @@ config OPTIMIZE_INLINING If unsure, say N. +config DEBUG_ENTRY + bool "Debug low-level entry code" + depends on DEBUG_KERNEL + ---help--- + This option enables sanity checks in x86's low-level entry code. + Some of these sanity checks may slow down kernel entries and + exits or otherwise impact performance. + + This is currently used to help test NMI code. + + If unsure, say N. + config DEBUG_NMI_SELFTEST bool "NMI Selftest" depends on DEBUG_KERNEL && X86_LOCAL_APIC diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S index 5422bd20bdf4..8cb3e438f21e 100644 --- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -1454,6 +1454,21 @@ first_nmi: /* Everything up to here is safe from nested NMIs */ +#ifdef CONFIG_DEBUG_ENTRY + /* + * For ease of testing, unmask NMIs right away. Disabled by + * default because IRET is very expensive. + */ + pushq $0 /* SS */ + pushq %rsp /* RSP (minus 8 because of the previous push) */ + addq $8, (%rsp) /* Fix up RSP */ + pushfq /* RFLAGS */ + pushq $__KERNEL_CS /* CS */ + pushq $1f /* RIP */ + INTERRUPT_RETURN /* continues at repeat_nmi below */ +1: +#endif + repeat_nmi: /* * If there was a nested NMI, the first NMI's iret will return -- 2.34.1