Re: [Xen-devel] [RFC] xen/arm: Handling cache maintenance instructions by set/way

[Julien Grall <julien.grall@xxxxxxxxxx>]

On 12/06/2017 03:24 PM, George Dunlap wrote:
> On 12/06/2017 03:19 PM, Julien Grall wrote:
> > Hi Konrad,
> >
> > On 12/06/2017 03:10 PM, Konrad Rzeszutek Wilk wrote:
> > > .snip..
> > > > The suggested policy is based on the KVM one:
> > > >      - If we trap a S/W instructions, we enable VM trapping (e.g
> > > > HCR_EL2.TVM) to
> > > > detect cache being turned on/off, and do a full clean.
> > > >      - We flush the caches on both caches being turned on and off.
> > > >      - Once the caches are enabled, we stop trapping VM instructions.
> > > >
> > > > Doing a full clean will require to go through the P2M and flush the
> > > > entries
> > > > one by one. At the moment, all the memory is mapped. As you can imagine
> > > > flushing guest with hundreds of MB will take a very long time (Linux
> > > > timeout
> > > > during CPU bring).
> > > Yikes. Since you mention 'based on the KVM one' - did they solve this
> > > particular
> > > problem or do they also have the same issue?
> > KVM is using populate on demand by default.
> If I understand properly, it's probably more accurate to say that KVM
> uses "allocate on demand".  The complicated part of populate-on-demand
> is the fact that it's not allowed to allocate anything.
Hmmm yes. You are right on the wording.

Cheers,

--
Julien Grall

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel