Messages in this thread Patch in this message | | | Date | Tue, 05 Jan 2010 12:02:14 -0800 | From | Greg KH <> | Subject | [18/39] x86, cpuid: Add "volatile" to asm in native_cpuid() |
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2.6.31-stable review patch. If anyone has any objections, please let us know.
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From: Suresh Siddha <suresh.b.siddha@intel.com>
commit 45a94d7cd45ed991914011919e7d40eb6d2546d1 upstream.
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 <suresh.b.siddha@intel.com> LKML-Reference: <1261009542.2745.55.camel@sbs-t61.sc.intel.com> Signed-off-by: H. Peter Anvin <hpa@zytor.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
--- arch/x86/include/asm/processor.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/arch/x86/include/asm/processor.h +++ b/arch/x86/include/asm/processor.h @@ -179,7 +179,7 @@ static inline void native_cpuid(unsigned 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),
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