Re: [Xen-devel] [PATCH v3 2/6] VMX: Properly handle pi when all the assigned devices are removed

["Wu, Feng" <feng.wu@xxxxxxxxx>]

> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: Thursday, September 1, 2016 4:21 PM
> To: Wu, Feng <feng.wu@xxxxxxxxx>
> Cc: andrew.cooper3@xxxxxxxxxx; dario.faggioli@xxxxxxxxxx;
> george.dunlap@xxxxxxxxxxxxx; Tian, Kevin <kevin.tian@xxxxxxxxx>; xen-
> devel@xxxxxxxxxxxxx
> Subject: Re: [PATCH v3 2/6] VMX: Properly handle pi when all the assigned
> devices are removed
> 
> >>> On 31.08.16 at 05:56, <feng.wu@xxxxxxxxx> wrote:
> > This patch handles some concern cases when the last assigned device
> > is removed from the domain. In this case we should carefully handle
> > pi descriptor and the per-cpu blocking list, to make sure:
> > - all the PI descriptor are in the right state when next time a
> > devices is assigned to the domain again.
> > - No remaining vcpus of the domain in the per-cpu blocking list.
> >
> > Basically, we pause the domain before zapping the PI hooks and
> > removing the vCPU from the blocking list, then unpause it after
> > that.
> >
> > Signed-off-by: Feng Wu <feng.wu@xxxxxxxxx>
> 
> Looks plausible, but
> a) as already for patch 1 I'm missing information on what changed
>    since v2 and

The biggest changes since v2 is that we use domain pause/unpause
(suggested by George) to handle the concern case, while v2 was using
some ugly and tricky method to do it, which was considered as hard
to maintain.

> b) doesn't this make unnecessary patch 1?

The purpose of patch 1 is to make sure the two hooks are installed
while CPU side PI is available event VT-d PI is not supported, I cannot
see why this patch will make it unnecessary.

Thanks,
Feng

> 
> Jan


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