Re: [Xen-devel] [PATCH RFC V7 4/5] xen, libxc: Request page fault injection via libxc

[Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>]

On 08/26/14 18:49, Jan Beulich wrote:
>>>> On 26.08.14 at 16:56, <rcojocaru@xxxxxxxxxxxxxxx> wrote:
>> On 08/26/2014 05:44 PM, Jan Beulich wrote:
>>>>>> On 26.08.14 at 16:24, <rcojocaru@xxxxxxxxxxxxxxx> wrote:
>>>> On 08/26/2014 05:13 PM, Jan Beulich wrote:
>>>>>>>> On 13.08.14 at 17:28, <rcojocaru@xxxxxxxxxxxxxxx> wrote:
>>>>>> --- a/xen/include/asm-x86/hvm/domain.h
>>>>>> +++ b/xen/include/asm-x86/hvm/domain.h
>>>>>> @@ -141,6 +141,14 @@ struct hvm_domain {
>>>>>>       */
>>>>>>      uint64_t sync_tsc;
>>>>>>  
>>>>>> +    /* Memory introspection page fault injection data. */
>>>>>> +    struct {
>>>>>> +        uint64_t address_space;
>>>>>> +        uint64_t virtual_address;
>>>>>> +        uint32_t errcode;
>>>>>> +        bool_t valid;
>>>>>> +    } fault_info;
>>>>>
>>>>> Sorry for noticing this only now, but how can this be a per-domain
>>>>> thing rather than a per-vCPU one?
>>>>
>>>> The requirement for our introspection application has simply been to
>>>> bring back in a swapped-out page, regardless of what VCPU ends up
>>>> actually doing it.
>>>
>>> But please remember that what you add to the public code base
>>> shouldn't be tied to specific needs of your application, it should
>>> be coded in a generally useful way.
>>
>> Of course, perhaps I should have written "the scenario we're working
>> with" rather than "the requirement for our application". I'm just trying
>> to understand all the usual cases for this.
>>
>>> Furthermore, how would this work if you have 2 vCPU-s hit such
>>> a condition, and you need to bring in 2 pages in parallel?
>>
>> Since this is all happening in the context of processing mem_events,
>> it's not really possible for two VCPUs to need to do this in parallel,
>> since processing mem_events is being done sequentially. A VCPU needs to
>> put a mem_event in the ring buffer and pause before this hypercall can
>> be called from userspace.
> 
> I'd certainly want to hear Tim's opinion here before settling on
> either model. Considering that this is at least mem-event related,
> it's slightly odd you didn't copy him in the first place.

Sorry about that, scripts/get_maintainter.pl did not list him and I
forgot to CC him.


Thanks,
Razvan Cojocaru

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