Re: [PATCH] mm/x86/pat: Only untrack the pfn range if unmap region

Peter Xu
2024-07-17T18:10:30Z

On Wed, Jul 17, 2024 at 01:31:54PM -0300, Jason Gunthorpe wrote:
> On Wed, Jul 17, 2024 at 12:30:19PM -0400, Peter Xu wrote:
> > On Wed, Jul 17, 2024 at 04:17:12PM +0200, David Hildenbrand wrote:
> > > I'd be curious how a previous truncation on a file can tear down a PFNMAP
> > > mapping -- and if there are simple ways to forbid that (if possible).
> >
> > Unfortunately, forbiding it may not work for vfio, as vfio would like to
> > allow none (or partial) mapping on the bars.. at least so far that's the
> > plan.
>
> vfio doesn't support truncation? Or does that means something else
> here?

Here I meant VFIO can explicitly zapping pgtables via vfio_pci_zap_bars(),
irrelevant of any form of truncations. I suppose it'll have the same
effect where we may need to stop assuming PFNMAP vmas will always have
fully installed pgtables.

Thanks,

--
Peter Xu