[bug report] drm/xe/svm: Implement prefetch support for SVM ranges

[Simona Vetter]

On Tue, Jun 03, 2025 at 07:29:52PM -0300, Jason Gunthorpe wrote:
> On Mon, May 26, 2025 at 10:15:17PM +0530, Ghimiray, Himal Prasad wrote:
> > 
> > 
> > On 26-05-2025 20:36, Dan Carpenter wrote:
> > > Hello Himal Prasad Ghimiray,
> > > 
> > > Commit 09ba0a8f06cd ("drm/xe/svm: Implement prefetch support for SVM
> > > ranges") from May 13, 2025 (linux-next), leads to the following
> > > Smatch static checker warning:
> > > 
> > > 	drivers/gpu/drm/xe/xe_vm.c:2922 prefetch_ranges()
> > > 	warn: passing positive error code 's32min-(-96),(-94)-(-15),(-13)-(-12),(-10)-(-2),1' to 'ERR_PTR'
> > 
> > Hi Dan,
> > 
> > Thanks for pointing this out. I see there's a gap in how hmm_range_fault()
> > adheres to its documented behavior. I believe the function should sanitize
> > positive return values from walk_page_range() to ensure consistency.
> > 
> > Jason can comment further on same.
> 
> Yeah, I don't think it should return positive error code, whatever is
> doing that should be fixed. Can you send a patch?

Not sure that's what's going on, from the comment and reading the code
(albeit non-exhaustively) I think you can only get positive error return
values from walk_page_range if the ops you provide do so. The hmm ones
don't, so I think this should be ok without any code changes?

Maybe a WARN_ON and patching that up for paranoia, but I don't see how
this can happen.

Cheers, Sima
-- 
Simona Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch