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

[Boris Ostrovsky <boris.ostrovsky@oracle.com>]

On 04/08/2014 03:15 AM, Jan Beulich wrote:
>>>> On 07.04.14 at 17:21, <boris.ostrovsky@oracle.com> wrote:
>> 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)?
> Generally I think code like this implies that you know the specification:
> eax here represents the maximum supported subleaf, and hence
> needs to be limited rather than masked.

All specs that I have say that bits of CPUID Fn0000_0007_EAX_x0 are 
reserved.

-boris