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

[Ghimiray, Himal Prasad]

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.
  >
> drivers/gpu/drm/xe/xe_vm.c
>      2917
>      2918                 err = xe_svm_range_get_pages(vm, svm_range, &ctx);
>      2919                 if (err) {
>      2920                         if (err == -EOPNOTSUPP || err == -EFAULT || err == -EPERM)
>      2921                                 err = -ENODATA;
> --> 2922                         drm_dbg(&vm->xe->drm, "Get pages failed, asid=%u, gpusvm=%p, errno=%pe\n",
>      2923                                 vm->usm.asid, &vm->svm.gpusvm, ERR_PTR(err));
> 
> The comments on walk_page_range() say it can return > 0 on success but
> the comments on hmm_range_fault() say it can never return > 0.  Smatch
> does a naive reading of the code and thinks that it can return > 0.
> 
> Presumably the comments are correct but the code is too tricky for me.
> 
> I can easily silence this in Smatch by adding deleting the positive
> returns from hmm_range_fault() from the cross function DB.  Can someone
> confirm that's the correct thing to do?
> 
>      2924                         return err;
>      2925                 }
>      2926                 xe_svm_range_debug(svm_range, "PREFETCH - RANGE GET PAGES DONE");
>      2927         }
>      2928
>      2929         return err;
>      2930 }
> 
> regards,
> dan carpenter