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Subject[PATCH v2 2/4] x86/split_lock: Align x86_capability to unsigned long to avoid split locked access
Date
set_cpu_cap() calls locked BTS and clear_cpu_cap() calls locked BTR to
operate on bitmap defined in x86_capability.

Locked BTS/BTR accesses a single unsigned long location. In 64-bit mode,
the location is at:
base address of x86_capability + (bit offset in x86_capability % 64) * 8

Since base address of x86_capability may not aligned to unsigned long,
the single unsigned long location may cross two cache lines and
accessing the location by locked BTS/BTR intructions will trigger #AC.

To fix the split lock issue, align x86_capability to unsigned long so that
the location will be always within one cache line.

Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
---
arch/x86/include/asm/processor.h | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index cfd29ee8c3da..5ad6ba4657a2 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -105,7 +105,8 @@ struct cpuinfo_x86 {
__u32 extended_cpuid_level;
/* Maximum supported CPUID level, -1=no CPUID: */
int cpuid_level;
- __u32 x86_capability[NCAPINTS + NBUGINTS];
+ __u32 x86_capability[NCAPINTS + NBUGINTS]
+ __aligned(sizeof(unsigned long));
char x86_vendor_id[16];
char x86_model_id[64];
/* in KB - valid for CPUS which support this call: */
--
2.5.0
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