From 45a94d7cd45ed991914011919e7d40eb6d2546d1 Mon Sep 17 00:00:00 2001 From: Suresh Siddha Date: Wed, 16 Dec 2009 16:25:42 -0800 Subject: [PATCH] x86, cpuid: Add "volatile" to asm in native_cpuid() xsave_cntxt_init() does something like: cpuid(0xd, ..); // find out what features FP/SSE/.. etc are supported xsetbv(); // enable the features known to OS cpuid(0xd, ..); // find out the size of the context for features enabled Depending on what features get enabled in xsetbv(), value of the cpuid.eax=0xd.ecx=0.ebx changes correspondingly (representing the size of the context that is enabled). As we don't have volatile keyword for native_cpuid(), gcc 4.1.2 optimizes away the second cpuid and the kernel continues to use the cpuid information obtained before xsetbv(), ultimately leading to kernel crash on processors supporting more state than the legacy FP/SSE. Add "volatile" for native_cpuid(). Signed-off-by: Suresh Siddha LKML-Reference: <1261009542.2745.55.camel@sbs-t61.sc.intel.com> Cc: stable@kernel.org Signed-off-by: H. Peter Anvin --- arch/x86/include/asm/processor.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h index 6f8ec1c37e0a..fc801bab1b3b 100644 --- a/arch/x86/include/asm/processor.h +++ b/arch/x86/include/asm/processor.h @@ -181,7 +181,7 @@ static inline void native_cpuid(unsigned int *eax, unsigned int *ebx, unsigned int *ecx, unsigned int *edx) { /* ecx is often an input as well as an output. */ - asm("cpuid" + asm volatile("cpuid" : "=a" (*eax), "=b" (*ebx), "=c" (*ecx), -- 2.30.2