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-rw-r--r--arch/x86/Kconfig.debug12
-rw-r--r--arch/x86/entry/entry_64.S15
2 files changed, 27 insertions, 0 deletions
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