Re: RE: [PATCH 01/13] Nested Virtualization: tools

[Andre Przywara <andre.przywara@amd.com>]

Dong, Eddie wrote:
> Dong, Eddie wrote:
>> # HG changeset patch
>> # User cegger
>> # Date 1283345869 -7200
>> tools: Add nestedhvm guest config option
>>
>> diff -r 80ef08613ec2 -r ecec3d163efa tools/libxc/xc_cpuid_x86.c
>> --- a/tools/libxc/xc_cpuid_x86.c
>> +++ b/tools/libxc/xc_cpuid_x86.c
>> @@ -30,7 +30,7 @@
>>  #define set_bit(idx, dst)   ((dst) |= (1u << ((idx) & 31)))
>>
>>  #define DEF_MAX_BASE 0x0000000du
>> -#define DEF_MAX_EXT  0x80000008u
>> +#define DEF_MAX_EXT  0x8000000au
> 
> How can this make Intel CPU happy?
> You may refer to my previous comments in V2.
Correct me if I am wrong, but this is only a max boundary:
tools/libxc/xc_cpuid_x86.c:234
     case 0x80000000:
         if ( regs[0] > DEF_MAX_EXT )
             regs[0] = DEF_MAX_EXT;
         break;
So if an Intel CPU returns 0x80000008 here, this will be in the regs[0] 
field and thus any higher value in DEF_MAX_EXT does not affect the 
guest's CPUID response.
So as long as Intel CPUs don't return higher values which don't match 
the AMD assignment (which is extremely unlikely), extending DEF_MAX_EXT 
is fine.

Regards,
Andre.

-- 
Andre Przywara
AMD-OSRC (Dresden)
Tel: x29712