[Xen-devel] [PATCH v2 01/30] xen/x86: Drop X86_FEATURE_3DNOW_ALT

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

Introducing an X86_FEATURE aliased value turns out to complicate automatic
processing of the feature list.  Drop X86_FEATURE_3DNOW_ALT and use
X86_FEATURE_PBE, extending the comment accordingly.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>

New in v2
---
 xen/arch/x86/cpu/amd.c           | 9 ++++++---
 xen/include/asm-x86/cpufeature.h | 1 -
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/xen/arch/x86/cpu/amd.c b/xen/arch/x86/cpu/amd.c
index 8ec841b..1ac44e0 100644
--- a/xen/arch/x86/cpu/amd.c
+++ b/xen/arch/x86/cpu/amd.c
@@ -440,9 +440,12 @@ static void init_amd(struct cpuinfo_x86 *c)
                wrmsrl(MSR_K7_HWCR, value);
        }
 
-       /* Bit 31 in normal CPUID used for nonstandard 3DNow ID;
-          3DNow is IDd by bit 31 in extended CPUID (1*32+31) anyway */
-       __clear_bit(X86_FEATURE_3DNOW_ALT, c->x86_capability);
+       /*
+        * Some AMD CPUs duplicate the 3DNow bit in base and extended CPUID
+        * leaves.  Unfortunately, this aliases PBE on Intel CPUs. Clobber the
+        * alias, leaving 3DNow in the extended leaf.
+        */
+       __clear_bit(X86_FEATURE_PBE, c->x86_capability);
        
        if (c->x86 == 0xf && c->x86_model < 0x14
            && cpu_has(c, X86_FEATURE_LAHF_LM)) {
diff --git a/xen/include/asm-x86/cpufeature.h b/xen/include/asm-x86/cpufeature.h
index 23f9fb2..6583039 100644
--- a/xen/include/asm-x86/cpufeature.h
+++ b/xen/include/asm-x86/cpufeature.h
@@ -45,7 +45,6 @@
 #define X86_FEATURE_ACC                (0*32+29) /* Automatic clock control */
 #define X86_FEATURE_IA64       (0*32+30) /* IA-64 processor */
 #define X86_FEATURE_PBE                (0*32+31) /* Pending Break Enable */
-#define X86_FEATURE_3DNOW_ALT  (0*32+31) /* AMD nonstandard 3DNow (Aliases 
PBE) */
 
 /* AMD-defined CPU features, CPUID level 0x80000001, word 1 */
 /* Don't duplicate feature flags which are redundant with Intel! */
-- 
2.1.4


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