Re: [PATCH v4] drm/vmwgfx: Treat zero SVGA_REG_CURSOR_MAX_DIMENSION as unset

[Maaz Mombasawala]

On 8/30/26 8:16 AM, fausten wrote:
> The cursor plane code validates cursor dimensions against
> SVGA_REG_CURSOR_MAX_DIMENSION before every cursor update, and
> rejects the update with -EINVAL if the cursor is larger than the
> reported maximum.
> 
> However, this register is only available on hardware versions 18
> and above, which introduced cursor MOBs. Older hardware (e.g. a
> VMware Fusion guest with SVGA version 2) returns 0 for it.
> In that case every cursor update is rejected,
> and the log is spammed with:
> 
>   [drm] Cursor dimensions (64, 64) exceed device max 0
> 
> The visible symptom is that the hardware cursor never appears at
> all on VMware Fusion guests (SVGA version 2), making the mouse
> pointer invisible even though the input devices work fine.
> 
> Treat a reported maximum of 0 as "not implemented" and skip the
> dimension check in that case, restoring the pre-existing behaviour
> of accepting the cursor.
> 
> Tested on VMware Fusion with an SVGA version 2 device where the
> cursor previously did not show up.
> 
> Fixes: d5ed8749168a ("drm/vmwgfx: enforce cursor size limits for MOB cursors")
> Signed-off-by: Yunfeng Li <yunfeng.li.nb@xxxxxxxxx>
> ---
>  drivers/gpu/drm/vmwgfx/vmwgfx_cursor_plane.c | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
> 
> ---
> Changes in v3:
> - Use an explicit cursor_max_dim > 0 comparison (Maaz).
> - Fix the comments: the register requires cursor MOBs which exist
>   only on hw version 18 and above; it is not Fusion-specific
>   (Maaz).
> 
> diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_cursor_plane.c b/drivers/gpu/drm/vmwgfx/vmwgfx_cursor_plane.c
> index d1e7df500..3d4660684 100644
> --- a/drivers/gpu/drm/vmwgfx/vmwgfx_cursor_plane.c
> +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_cursor_plane.c
> @@ -237,8 +237,10 @@ static int vmw_cursor_mob_get(struct vmw_cursor_plane *vcp,
>  	mob_max_size = vmw_read(dev_priv, SVGA_REG_MOB_MAX_SIZE);
>  	cursor_max_dim = vmw_read(dev_priv, SVGA_REG_CURSOR_MAX_DIMENSION);
>  
> -	if (size > mob_max_size || vps->base.crtc_w > cursor_max_dim ||
> -	    vps->base.crtc_h > cursor_max_dim)
> +	/* Cursor MOBs, and thus this register, exist only on hw version 18+. */
> +	if (cursor_max_dim > 0 &&
> +	    (size > mob_max_size || vps->base.crtc_w > cursor_max_dim ||
> +	     vps->base.crtc_h > cursor_max_dim))
>  		return -EINVAL;
>  
>  	if (vps->cursor.mob) {
> @@ -748,8 +750,10 @@ int vmw_cursor_plane_atomic_check(struct drm_plane *plane,
>  		u32 cursor_max_dim =
>  			vmw_read(vmw, SVGA_REG_CURSOR_MAX_DIMENSION);
>  
> -		if (new_state->crtc_w > cursor_max_dim ||
> -		    new_state->crtc_h > cursor_max_dim) {
> +		/* Cursor MOBs, and thus this register, exist only on hw version 18+. */
> +		if (cursor_max_dim > 0 &&
> +		    (new_state->crtc_w > cursor_max_dim ||
> +		     new_state->crtc_h > cursor_max_dim)) {
>  			drm_warn(&vmw->drm,
>  				 "Cursor dimensions (%d, %d) exceed device max %u\n",
>  				 new_state->crtc_w, new_state->crtc_h,

This patch bricked my testing VM, investigating..


-- 
Maaz Mombasawala <maaz.mombasawala@xxxxxxxxxxxx>