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

[Dan Carpenter]

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'

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