From: Suresh Siddha Date: Thu, 17 Dec 2009 00:25:42 +0000 (-0800) Subject: x86, cpuid: Add "volatile" to asm in native_cpuid() X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=45a94d7cd45ed991914011919e7d40eb6d2546d1;p=GitHub%2Fexynos8895%2Fandroid_kernel_samsung_universal8895.git 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 --- 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),