Re: [Xen-devel] [PATCH v5] x86/emulate: Send vm_event from emulate

[Alexandru Stefan ISAILA <aisaila@xxxxxxxxxxxxxxx>]

On 01.07.2019 18:53, Jan Beulich wrote:
> On 01.07.2019 17:36, Alexandru Stefan ISAILA wrote:
>> On 01.07.2019 17:55, Jan Beulich wrote:
>>> On 01.07.2019 16:45, Alexandru Stefan ISAILA wrote:
>>>> On 01.07.2019 16:13, Jan Beulich wrote:
>>>>>>>> On 04.06.19 at 13:49, <aisaila@xxxxxxxxxxxxxxx> wrote:
>>>>>> +    if ( !req.u.mem_access.flags )
>>>>>> +        return false; /* no violation */
>>>>>
>>>>> How is the "false" here (I think this is the one the description talks
>>>>> about) matching up with the various other ones in the function?
>>>>
>>>> There should be no event if there is no access violation. So in this
>>>> case the emulation is continued as expected.
>>>
>>> But this doesn't answer my question: You use "false" as return value
>>> to indicate different things. Only the one here means "no access
>>> violation".
>>
>> Sorry about that, since this will remain the only return false apart
>> form the main one (return monitor_traps()), false  = event was not sent
>> and true = event was sent.
>>
>> I understand that you are asking about the scenario when there was a
>> violation and the event was not sent. Then I can issue a domain_crash()
>> as that is potentially a big issue.
>>
>> I hope I got that correctly.
> 
> I don't get the impression that you did. I count a total of four
> "return false" in the function, only one of which explicitly means
> "no access violation" (others may have that meaning implicitly). Let's
> take the p2m_get_mem_access() failure case as an example: What I don't
> understand is why this case and the "no access violation" one are both
> meant to be treated the same.

Right, at the moment, false means that emulation should continue and 
true means that emulation should stop. If it is a must that I return 
different errors I will change that in the next version but in the way 
that the code is right now they will be treated the same way.
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