For 4.17 (was: Re: [PATCH v3 0/2] Move calls to memory_type_changed())

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Thu, Sep 29, 2022 at 12:14:10PM +0200, Jan Beulich wrote:
> On 28.09.2022 16:11, Roger Pau Monne wrote:
> > The current calls to memory_type_changed() are wider than strictly
> > necessary.  Move them inside the iocap handlers and also limit to only
> > issue them when required.
> > 
> > I would really like to get some feedback on the Arm change, since this
> > is now a prereq for the actual fix.
> > 
> > Thanks, Roger.
> > 
> > Roger Pau Monne (2):
> >   arm/vgic: drop const attribute from gic_iomem_deny_access()
> >   x86/ept: limit calls to memory_type_changed()
> 
> Are there intentions for having these on 4.17?

I wasn't sure.  From XenServer PoV it's certainly a bug fix,
otherwise some workloads related to GPU passthrough are simply too
slow to be usable.

I would certainly be fine with it making it's way into 4.17, let me
add Henry:

Cons:
 - Changes the number of issued memory_type_changed(), so there's a
   risk I misplaced some of the conditions and we end up with wrong
   cache types in the guest p2m due to missing memory_type_changed()
   calls.  That however won't affect Xen itself, just the guest.

Pros:
 - Removes unneeded memory_type_changed(), thus making some operations
   faster.  It's effect it's greatly dependent on using a set of
   hypercalls against a domain, which doesn't seem common in upstream.
   It's possible other products based on Xen apart from XenServer will
   also see an speedup as a result.

Thanks, Roger.