Re: [Xen-devel] [PATCH] Fix PV CPUID virtualization of XSave

[Haitao Shan <maillists.shan@xxxxxxxxx>]

2011/9/16 Jan Beulich <JBeulich@xxxxxxxx>:
>>>> On 16.09.11 at 02:46, Haitao Shan <maillists.shan@xxxxxxxxx> wrote:
>> Hi, Keir,
>>
>> The patch will fix XSave CPUID virtualization for PV guests. The XSave
>> area size returned by CPUID leaf D is changed dynamically depending on
>> the XCR0. Tools/libxc only assigns a static value. The fix will adjust
>> xsave area size during runtime.
>>
>> Note: This fix is already in HVM cpuid virtualization. And Dom0 is not
>> affected, either.
>>
>> Signed-off-by:  Shan Haitao <haitao.shan@xxxxxxxxx>
>>
>> Shan Haitao
>>
>> diff -r 5fe770c8a8a3 xen/arch/x86/traps.c
>> --- a/xen/arch/x86/traps.c    Tue Sep 06 15:49:40 2011 +0100
>> +++ b/xen/arch/x86/traps.c    Wed Sep 07 02:09:12 2011 +0800
>> @@ -770,6 +770,30 @@ static void pv_cpuid(struct cpu_user_reg
>>      {
>>          if ( !cpuid_hypervisor_leaves(a, c, &a, &b, &c, &d) )
>>              domain_cpuid(current->domain, a, c, &a, &b, &c, &d);
>> +
>> +        switch ( a )
>> +        {
>> +        case 0xd:
>> +        {
>> +            unsigned int sub_leaf, _eax, _ebx, _ecx, _edx;
>> +            /* EBX value of main leaf 0 depends on enabled xsave features
>> */
>> +            if ( c == 0 && current->arch.xcr0 )
>> +            {
>> +                /* reset EBX to default value first */
>> +                b = XSTATE_AREA_MIN_SIZE;
>> +                for ( sub_leaf = 2; sub_leaf < 64; sub_leaf++ )
>
> Shouldn't the upper bound be 63 here (as bit 63 serves a different
> purpose, and if that bit was set code changes would be required in
> various other places)?
>
> Jan
Nice catch! I will update the patch. The same piece of code is
borrowed from hvm_cpuid(), where I can change the value from 64 to 63,
too.

Shan Haitao

>
>> +                {
>> +                    if ( !(current->arch.xcr0 & (1ULL << sub_leaf)) )
>> +                        continue;
>> +                    domain_cpuid(current->domain, a, c, &_eax, &_ebx, &_ecx,
>> +                                 &_edx);
>> +                    if ( (_eax + _ebx) > b )
>> +                        b = _eax + _ebx;
>> +                }
>> +            }
>> +        break;
>> +        }
>> +        }
>>          goto out;
>>      }
>
>
>
>

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