Claude review: drm/gem-shmem: Return vm_fault_t from drm_gem_shmem_try_map_pmd()

[Claude Code Review Bot <claude-review@example.com>]

Patch Review

**Review:**

Good API improvement suggested by Matthew Wilcox. Changes from boolean return to proper fault status:

```c
-static bool drm_gem_shmem_try_map_pmd(...)
+static vm_fault_t drm_gem_shmem_try_map_pmd(...)
```

**Before:**
```c
if (drm_gem_shmem_try_map_pmd(vmf, vmf->address, page)) {
    ret = VM_FAULT_NOPAGE;
    goto out;
}
```

**After:**
```c
ret = drm_gem_shmem_try_map_pmd(vmf, vmf->address, page);
if (ret == VM_FAULT_NOPAGE)
    goto out;
```

This is cleaner and allows the function to propagate error codes properly. The function now returns:
- `VM_FAULT_NOPAGE` if PMD mapping succeeded
- `0` if PMD mapping didn't happen (fall through to regular PFN mapping)
- Potentially error codes from `vmf_insert_pfn_pmd()`

**Issue - Incomplete error handling:**
The caller only checks for `VM_FAULT_NOPAGE`:
```c
ret = drm_gem_shmem_try_map_pmd(vmf, vmf->address, page);
if (ret == VM_FAULT_NOPAGE)
    goto out;
```

**What if `vmf_insert_pfn_pmd()` returns an error?** The code will fall through and attempt regular PFN insertion. Is this intentional fallback behavior or a bug?

Looking at the code flow:
1. If `ret == VM_FAULT_NOPAGE`: success, return
2. If `ret == 0`: PMD not attempted, fall through to regular PFN (correct)
3. If `ret == VM_FAULT_ERROR`: PMD failed, fall through to regular PFN (questionable)

**Verdict:** ⚠ Need clarification on error handling - should errors from PMD insertion fall through to regular PFN or be propagated?

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Generated by Claude Code Patch Reviewer