Re: [Xen-devel] [PATCH] x86: cap address bits CPUID output

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 09.05.16 at 14:35, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 02/05/16 16:11, Jan Beulich wrote:
>> --- a/xen/arch/x86/e820.c
>> +++ b/xen/arch/x86/e820.c
>> @@ -451,11 +451,11 @@ static uint64_t __init mtrr_top_of_ram(v
>>           return 0;
>>  
>>      /* Find the physical address size for this CPU. */
>> -    cpuid(0x80000000, &eax, &ebx, &ecx, &edx);
>> -    if ( eax >= 0x80000008 )
>> +    if ( cpuid_eax(0x80000000) >= 0x80000008 )
> 
> You indicated in review of my cpuid series that this check is buggy, and
> the upper half needs comparing exactly to 0x8000.

Oh, indeed. How did I forget?

> It occurs to me that early_cpu_detect() really should be callled
> earlier, to avoid needing to recalculate this information.

Well, I had (briefly) looked at that option, but iirc it didn't
seem feasible to move it up as early as we'd need it to be.

Jan


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