Re: [Xen-devel] [PATCH 3/7] vm-event: introduce vm_event_vcpu_enter

[Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>]

On 06/16/16 23:10, Corneliu ZUZU wrote:
> On 6/16/2016 5:51 PM, Jan Beulich wrote:
>>>>> On 16.06.16 at 16:08, <czuzu@xxxxxxxxxxxxxxx> wrote:
>>> @@ -509,6 +508,8 @@ void hvm_do_resume(struct vcpu *v)
>>>           }
>>>       }
>>>   +    vm_event_vcpu_enter(v);
>> Why here?
> Why indeed. It made sense because monitor_write_data handling was
> originally there and then the plan was to move it to vm_event_vcpu_enter
> (which happens in the following commit).
> The question is though, why was monitor_write_data handled there in the
> first place? Why was it not put e.g. in vmx_do_resume immediately after
> the call to hvm_do_resume and just before
> the reset_stack_and_jump...? And what happens with handling
> monitor_write_data if this:
> 
> if ( !handle_hvm_io_completion(v) )
>         return;
> 
> causes a return?

It's in hvm_do_resume() because, for one, that's the place that was
suggested (or at least confirmed when I've proposed it for such things)
on this list back when I wrote the code. And then it's here because
vmx_do_things()-type functions are, well, VMX, and I had hoped that by
choosing hvm-prefixed functions I'd get SVM support for free.

As for the handle_hvm_io_completion(v) return, my understanding was that
that would eventually cause another exit, and eventually we'd get to the
code below once the IO part is done.


Thanks,
Razvan

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