Re: [Xen-devel] xc_hvm_inject_trap() races

[Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>]

On 11/02/2016 11:30 AM, Jan Beulich wrote:
>>>> On 02.11.16 at 10:11, <rcojocaru@xxxxxxxxxxxxxxx> wrote:
>> On 11/02/2016 11:05 AM, Jan Beulich wrote:
>>>>>> On 02.11.16 at 09:57, <rcojocaru@xxxxxxxxxxxxxxx> wrote:
>>>> On 11/02/2016 10:49 AM, Jan Beulich wrote:
>>>>> The fact that {vmx,svm}_inject_trap() combine the new exception
>>>>> with an already injected one (and blindly discard events other than
>>>>> hw exceptions), otoh, looks like indeed wants to be controllable by
>>>>> the caller: When the event comes from the outside (the hypercall),
>>>>> it would clearly seem better to simply tell the caller that no injection
>>>>> happened and the event needs to be kept pending.
>>>>
>>>> However this is not possible with the current design, since all
>>>> xc_hvm_inject_trap() really does is set the info to be used at
>>>> hvm_do_resume() time. So at the time xc_hvm_inject_trap() returns, it's
>>>> not yet possible to know if the injection will succeed or not (assuming
>>>> we discard it when it would collide with another).
>>>
>>> That's my point - it shouldn't get discarded, but remain latched
>>> for a future invocation of hvm_do_resume(). Making
>>> hvm_inject_trap() have a suitable parameter (and a return value)
>>> would be the easy part of the change here. The difficult part would
>>> be to make sure the injection context is the right one.
>>
>> Should I then bring this patch back?
>>
>> https://lists.xen.org/archives/html/xen-devel/2014-07/msg02927.html 
>>
>> It has been rejected at the time on the grounds that
>> xc_hvm_inject_trap() is sufficient.
> 
> I don't think it would deal with all possible situations, the more
> that it's (already by its title) #PF specific. I think the named
> difficult part would need to be solved in the hypervisor alone,
> without further external information.

Found an earlier version of the patch, proposing to extend
HVMOP_inject_trap instead of a new libxc hypercall, which apparently got
so far as to have an "Acked-by" and a "Reviewed-by":

https://lists.xenproject.org/archives/html/xen-devel/2014-09/msg01244.html

Is this one worth bringing back with the new information?


Thanks,
Razvan

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