Re: [Xen-devel] [PATCH] mem_event: use wait queue when ring is full

["Andres Lagar-Cavilla" <andres@xxxxxxxxxxxxxxxx>]

> On Mon, Dec 05, Andres Lagar-Cavilla wrote:
>
>> > On Mon, Dec 05, Andres Lagar-Cavilla wrote:
>> >
>> >> > +    med->bit = bit;
>> >> I think it's been asked before for this to have a more expressive
>> name.
>> >
>> > I have to recheck, AFAIK it was the mem_bit where mem_ is redundant.
>> how about pause_flag?
>
> I made this change in my patch.
>
>> > Before this patch, mem_event_unpause_vcpus() was used to resume
>> waiters
>> > for the ring itself and for room in the ring.
>> > Now there is mem_event_wake_waiters(), which indicates the ring is
>> > active, and there is mem_event_wake_requesters() which indicates the
>> > ring has room to place guest requests.
>>
>> I think that if there is no ring where one is expected, harsher actions
>> should happen. That is what we do in our patch. e.g.
>> p2m_mem_paging_populate -> no ring -> crash domain, or
>> p2m_mem_access_check -> access_required -> no ring -> crash domain.
>>
>> That would eliminate wake_waiters, methinks?
>
> In p2m_mem_paging_populate() a sanity check could be added. I think it
> would indicate bad p2mt state because nominate was called without ring.
> How else can a gfn enter paging state?
Definitely. Crash that domain. Maybe the pager crashed and burned, or quit
carelessly.
Andres
>
> Olaf
>



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