Re: [PATCH v3 4/4] x86/PV: enable the emulated PIT

["Roger Pau Monné" <roger.pau@citrix.com>]

El 18/01/16 a les 8.43, Jan Beulich ha escrit:
>>>> On 15.01.16 at 18:45, <roger.pau@citrix.com> wrote:
>> Changes since v2:
>>  - Change 'if ( (a && b) || (!a && c) )' into 'if ( a ? b : c )'.
> 
> Thanks, but after some more thinking about it I'm afraid there are
> a few more aspects to consider here:
> 
>> --- a/xen/arch/x86/domain.c
>> +++ b/xen/arch/x86/domain.c
>> @@ -542,8 +542,9 @@ int arch_domain_create(struct domain *d, unsigned int domcr_flags,
>>                     d->domain_id, config->emulation_flags);
>>              return -EINVAL;
>>          }
>> -        if ( config->emulation_flags != 0 &&
>> -             (!is_hvm_domain(d) || config->emulation_flags != XEN_X86_EMU_ALL) )
>> +        if ( is_hvm_domain(d) ? (config->emulation_flags != XEN_X86_EMU_ALL &&
>> +             config->emulation_flags != 0) :
>> +             (config->emulation_flags != XEN_X86_EMU_PIT) )
>>          {
> 
> For one I think it would be a good idea to allow zero for PV domains,
> and perhaps even default new DomU-s to have the PIT flag clear.
> (Also - indentation.)

This sounds fine to me, but IMHO, it should be done in a separate patch.
This patch just restores previous behaviour for PV guests, then we can
move on from there.

> And then - is all this working as intended for the hwdom != Dom0
> case?

I have to admit I have not tried it, but AFAICT in the hwdom != Dom0
case the set of enabled emulated devices should be the same as a normal
guest, the hardware domain doesn't get any more or less emulated devices
than any other guest ATM.

Roger.