Re: [Xen-devel] [PATCH v2 21/30] x86/pv: Provide custom cpumasks for PV domains

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 17/02/16 08:13, Jan Beulich wrote:
>>>> On 05.02.16 at 14:42, <andrew.cooper3@xxxxxxxxxx> wrote:
>> --- a/xen/arch/x86/cpu/amd.c
>> +++ b/xen/arch/x86/cpu/amd.c
>> @@ -208,7 +208,9 @@ static void __init noinline probe_masking_msrs(void)
>>  static void amd_ctxt_switch_levelling(const struct domain *nextd)
>>  {
>>      struct cpuidmasks *these_masks = &this_cpu(cpuidmasks);
>> -    const struct cpuidmasks *masks = &cpuidmask_defaults;
>> +    const struct cpuidmasks *masks =
>> +            (nextd && is_pv_domain(nextd) && 
>> nextd->arch.pv_domain.cpuidmasks)
>> +            ? nextd->arch.pv_domain.cpuidmasks : &cpuidmask_defaults;
> Mixing tabs and spaces for indentation.
>
>> --- a/xen/arch/x86/domain.c
>> +++ b/xen/arch/x86/domain.c
>> @@ -574,6 +574,11 @@ int arch_domain_create(struct domain *d, unsigned int 
>> domcr_flags,
>>              goto fail;
>>          clear_page(d->arch.pv_domain.gdt_ldt_l1tab);
>>  
>> +        d->arch.pv_domain.cpuidmasks = xmalloc(struct cpuidmasks);
>> +        if ( !d->arch.pv_domain.cpuidmasks )
>> +            goto fail;
>> +        *d->arch.pv_domain.cpuidmasks = cpuidmask_defaults;
> Along the lines of not masking features for the hypervisor's own use
> (see the respective comment on the earlier patch) I think this patch,
> here or in domain_build.c, should except Dom0 from having the
> default masking applied. This shouldn't, however, extend to CPUID
> faulting. (Perhaps this rather belongs here so that the non-Dom0
> hardware domain case can also be taken care of.)

Very specifically not.  It is wrong to special case Dom0 and the
hardware domain, as their cpuid values should relevent to their VM, not
the host.

The default cpuid policy level with real hardware, so its no practical
change at this point.

~Andrew

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