[PATCH for-4.7] xen/hvm: Fix advertisment of available xstates following c/s c52319642

[Andrew Cooper <andrew.cooper3@citrix.com>]

PKU lives in CPUID.7[0].ECX, not EBX.  This causes hardware with BMI1 to
accidentally advertise PKU in CPUID.0xD[0].EAX.  Any OS which proceeds to
blindly write this into %xcr0 takes a #GP fault.  (Experimentally, Windows
Vista 32bit falls into this category.)

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
CC: Jan Beulich <JBeulich@suse.com>
CC: Wei Liu <wei.liu2@citrix.com>

This is all going to be far less error prone when I have guest_has_$FEATURE(v)
helpers which read the bits out of a flat array...
---
 xen/arch/x86/hvm/hvm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index e664b34..78db903 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -3466,7 +3466,7 @@ void hvm_cpuid(unsigned int input, unsigned int *eax, unsigned int *ebx,
                                   xstate_sizes[_XSTATE_BNDCSR]);
             }
 
-            if ( _ebx & cpufeat_mask(X86_FEATURE_PKU) )
+            if ( _ecx & cpufeat_mask(X86_FEATURE_PKU) )
             {
                 xfeature_mask |= XSTATE_PKRU;
                 xstate_size = max(xstate_size,
-- 
2.1.4


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