drm/xe/userptr: properly setup pfn_flags_mask

Currently we just leave it uninitialised, which at first looks harmless,
however we also don't zero out the pfn array, and with pfn_flags_mask
the idea is to be able set individual flags for a given range of pfn or
completely ignore them, outside of default_flags. So here we end up with
pfn[i] & pfn_flags_mask, and if both are uninitialised we might get back
an unexpected flags value, like asking for read only with default_flags,
but getting back write on top, leading to potentially bogus behaviour.

To fix this ensure we zero the pfn_flags_mask, such that hmm only
considers the default_flags and not also the initial pfn[i] value.

v2 (Thomas):
 - Prefer proper initializer.

Fixes: 81e058a3e7fd ("drm/xe: Introduce helper to populate userptr")
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@intel.com>
Cc: <stable@vger.kernel.org> # v6.10+
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Tejas Upadhyay <tejas.upadhyay@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250226174748.294285-2-matthew.auld@intel.com
(cherry picked from commit dd8c01e42f4c5c1eaf02f003d7d588ba6706aa71)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

diff --git a/drivers/gpu/drm/xe/xe_hmm.c b/drivers/gpu/drm/xe/xe_hmm.c
index 0898344678801ca902b6e850aa889a93114617c0..2e4ae61567d8d8db8c0cdb5900a590a0c537a532 100644 (file)
--- a/drivers/gpu/drm/xe/xe_hmm.c
+++ b/drivers/gpu/drm/xe/xe_hmm.c
@@ -166,13 +166,20 @@ int xe_hmm_userptr_populate_range(struct xe_userptr_vma *uvma,
 {
        unsigned long timeout =
                jiffies + msecs_to_jiffies(HMM_RANGE_DEFAULT_TIMEOUT);
-       unsigned long *pfns, flags = HMM_PFN_REQ_FAULT;
+       unsigned long *pfns;
        struct xe_userptr *userptr;
        struct xe_vma *vma = &uvma->vma;
        u64 userptr_start = xe_vma_userptr(vma);
        u64 userptr_end = userptr_start + xe_vma_size(vma);
        struct xe_vm *vm = xe_vma_vm(vma);
-       struct hmm_range hmm_range;
+       struct hmm_range hmm_range = {
+               .pfn_flags_mask = 0, /* ignore pfns */
+               .default_flags = HMM_PFN_REQ_FAULT,
+               .start = userptr_start,
+               .end = userptr_end,
+               .notifier = &uvma->userptr.notifier,
+               .dev_private_owner = vm->xe,
+       };
        bool write = !xe_vma_read_only(vma);
        unsigned long notifier_seq;
        u64 npages;
@@ -199,19 +206,14 @@ int xe_hmm_userptr_populate_range(struct xe_userptr_vma *uvma,
                return -ENOMEM;
 
        if (write)
-               flags |= HMM_PFN_REQ_WRITE;
+               hmm_range.default_flags |= HMM_PFN_REQ_WRITE;
 
        if (!mmget_not_zero(userptr->notifier.mm)) {
                ret = -EFAULT;
                goto free_pfns;
        }
 
-       hmm_range.default_flags = flags;
        hmm_range.hmm_pfns = pfns;
-       hmm_range.notifier = &userptr->notifier;
-       hmm_range.start = userptr_start;
-       hmm_range.end = userptr_end;
-       hmm_range.dev_private_owner = vm->xe;
 
        while (true) {
                hmm_range.notifier_seq = mmu_interval_read_begin(&userptr->notifier);