Claude review: rust: drm: gem: Add vmap functions to shmem bindings

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

Patch Review

**Status: Looks good overall, minor notes**

This is the largest patch in the series. Key design decisions are sound:

**VMap lifecycle**: The `make_vmap` method acquires the DMA reservation lock, calls `drm_gem_shmem_vmap_locked`, then explicitly drops the guard before potentially calling `raw_vunmap` (which re-acquires the lock). This avoids deadlock:

```rust
let guard = DmaResvGuard::new(self);
to_result(unsafe {
    bindings::drm_gem_shmem_vmap_locked(self.as_raw_shmem(), map.as_mut_ptr())
})?;
drop(guard);
```

**iomem rejection**: The iomem path correctly unmaps before returning an error:

```rust
if map.is_iomem {
    unsafe { self.raw_vunmap(map) };
    Err(ENOTSUPP)
}
```

**SGTableMap and Devres interaction**: The `SGTableMap` is wrapped in `Devres` and stored in a `LazyInit`. On device unbind, Devres drops the SGTableMap which calls `__drm_gem_shmem_free_sgt_locked()` and sets `shmem->sgt = NULL`. In `free_callback`, `sgt_res.reset()` is called before `drm_gem_shmem_release()`, ensuring no double-free since `drm_gem_shmem_release()` checks `if (shmem->sgt)`.

The reordering in `free_callback` is critical and correct — `sgt_res` must be reset while the GEM object's dma_resv is still valid:

```rust
unsafe { Pin::new_unchecked(&mut (*this).sgt_res) }.reset();
unsafe { bindings::drm_gem_shmem_release(base) };
let _ = unsafe { KBox::from_raw(this) };
```

**Device validation in `sg_table()`**: The check that the caller's device matches the GEM object's device is a good safety measure:

```rust
if dev.as_raw() != self.dev().as_ref().as_raw() {
    return Err(EINVAL);
}
```

**Test coverage**: The kunit tests are well-structured, covering size validation, IO read/write, and wrong-device rejection.

Minor observation on the vmap_io test: the test uses `0xFFFFFFFF` for write32 and checks individual bytes are all `0xFF` — this works regardless of endianness, which is nice.

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Generated by Claude Code Patch Reviewer