Re: [Xen-devel] xc_hvm_inject_trap() races

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> 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.

Jan


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