Re: [PATCH v1] drm/ttm: Refcount allocated tail pages

[Christian König]

Am 15.08.22 um 13:19 schrieb Dmitry Osipenko:
> [SNIP]
> > > > I'll try to dig out the older discussions, thank you for the quick
> > > > reply!
> > > Are you sure it was really discussed in public previously? All I can
> > > find is yours two answers to a similar patches where you're saying that
> > > this it's a wrong solution without in-depth explanation and further
> > > discussions.
> > Yeah, that's my problem as well I can't find that of hand.
> >
> > But yes it certainly was discussed in public.
> If it was only CC'd to dri-devel, then could be that emails didn't pass
> the spam moderation :/

That might be possible.

> > > Maybe it was discussed privately? In this case I will be happy to get
> > > more info from you about the root of the problem so I could start to
> > > look at how to fix it properly. It's not apparent where the problem is
> > > to a TTM newbie like me.
> > Well this is completely unfixable. See the whole purpose of TTM is to
> > allow tracing where what is mapped of a buffer object.
> >
> > If you circumvent that and increase the page reference yourself than
> > that whole functionality can't work correctly any more.
> Are you suggesting that the problem is that TTM doesn't see the KVM page
> faults/mappings?

Yes, and no. It's one of the issues, but there is more behind that (e.g. 
what happens when TTM switches from pages to local memory for backing a BO).

Another question is why is KVM accessing the page structure in the first 
place? The VMA is mapped with VM_PFNMAP and VM_IO, KVM should never ever 
touch any of those pages.

Regards,
Christian.