Re: [Xen-devel] [PATCH for-4.10] x86/hvm: Don't ignore unknown MSRs in the migration stream

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 20.11.17 at 15:10, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 17/11/17 12:10, Jan Beulich wrote:
>>>>> On 16.11.17 at 20:15, <andrew.cooper3@xxxxxxxxxx> wrote:
>>> Doing so amounts to silent state corruption, and must be avoided.
>> I think a little more explanation is needed on why the current code
>> is insufficient. Note specifically this
>>
>>     for ( i = 0; !err && i < ctxt->count; ++i )
>>     {
>>         switch ( ctxt->msr[i].index )
>>         {
>>         default:
>>             if ( !ctxt->msr[i]._rsvd )
>>                 err = -ENXIO;
>>             break;
>>         }
>>     }
>>
>> in hvm_load_cpu_msrs(), intended to give vendor code a first
>> shot, but allowing for vendor independent MSRs to be handled
>> here.
> 
> That is sufficiently subtle and non-obvious that I'm still having a hard
> time convincing myself that its correct.  Also, this use of _rsvd really
> should be document.

Well, from an abstract pov I agree. The field being defined in the
public interface though, I don't see a good place where to document
that - its point of declaration certainly isn't the right one in such a
case, as the public interface should not document implementation
details.

Jan


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