Re: [PATCH] drm/vmwgfx: Handle MOBs without page-table BOs

[Zack Rusin]

On Tue, Jul 7, 2026 at 11:05 AM Ruoyu Wang <ruoyuw560@xxxxxxxxx> wrote:
>
> Single-page MOBs and small OTable bases use depth-0 page-table entries
> and do not allocate a page-table BO. Their existing teardown paths were
> written to tolerate that by checking a local BO pointer before reserving
> or fencing it.
>
> Commit 668b206601c5 ("drm/vmwgfx: Stop using raw ttm_buffer_object's")
> changed pt_bo from a raw TTM buffer object pointer to a vmwgfx BO pointer
> and converted those local BO initializers to &pt_bo->tbo. That
> dereferences pt_bo before the existing NULL checks, so depth-0 MOBs can
> crash during OTable teardown or MOB unbind.

That analysis is incorrect. Nothing here can crash. &pt_bo->tbo is not
a dereference. It's address-of-member. tbo is the first member of
struct vmw_bo (offset 0) so &((struct vmw_bo *)NULL)->tbo evaluates to
exactly NULL. The entire patch is basically a no-op. If you have some
decent static checker that's being tricked by this code and there's
value in unblocking it, please describe your static checker and feel
free to resubmit as a code cleanup, but the above analysis and fhe
fixes tag are incorrect.

z

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