Re: [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