Re: [Xen-devel] [PATCH v2 2/3] x86/AMD: support further feature masking MSRs

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 04/07/2014 05:43 AM, Jan Beulich wrote:

@@ -179,11 +196,39 @@ static void __devinit set_cpuidmask(cons
        printk("Writing CPUID extended feature mask ECX:EDX -> %08Xh:%08Xh\n",
               extfeat_ecx, extfeat_edx);
 
+	if (c->cpuid_level >= 7)
+               cpuid_count(7, 0, &eax, &ebx, &ecx, &edx);
+       else
+               ebx = eax = 0;
+       if ((eax | ebx) && ~(l7s0_eax & l7s0_ebx)) {
+               if (l7s0_eax > eax)
+                       l7s0_eax = eax;
+               l7s0_ebx &= ebx;


Can you explain why eax is treated differently here (i.e. not ANDing it 
as is done with ebx)?
-boris


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