Re: [Xen-devel] xc_hvm_inject_trap() races

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 07.11.16 at 18:01, <rcojocaru@xxxxxxxxxxxxxxx> wrote:
> On 11/07/2016 06:10 PM, Jan Beulich wrote:
>>>>> On 07.11.16 at 16:24, <rcojocaru@xxxxxxxxxxxxxxx> wrote:
>>> The one-shot vm_event does sound reasonable. I could set a flag
>>> per-VCPU, basically similar to v->arch.hvm_vcpu.inject_trap.vector, and
>>> fire a single event from hvm_inject_trap() if it's set (then unset it) -
>>> the flag would be set via an xc_monitor_next_interrupt() call in libxc.
>> 
>> Doing this in hvm_inject_trap() would not cover all cases afict.
>> I'd suggest doing this from hvm_do_resume() _after_ the
>> (conditional) call to hvm_inject_trap(), if there is _any_ event
>> pending.
> 
> But that would only cover the hypercall-injected traps. The condition in
> hvm_do_resume() is "if ( v->arch.hvm_vcpu.inject_trap.vector != -1 )",
> and inject_trap.vector seems to only ever be set by the hypercall:
>[...]
> So if the next interrupt is not caused by the hypercall, we'll never get
> another event. Am I reading the code wrong?

No, maybe I expressed myself ambiguously: I meant to say that the
event should be delivered from hvm_do_resume(), but _outside_ the
conditional guarding the call to hvm_inject_trap(). Otherwise things
would have been worse than when doing it inside hvm_inject_trap().

Jan


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