Re: [PATCH] drm/vboxvideo: Vmap/vunmap cursor BO in prepare_fb and cleanup_fb

[Thomas Zimmermann <tzimmermann@suse.de>]

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Hi

Am 03.02.21 um 11:44 schrieb Daniel Vetter:
> On Wed, Feb 03, 2021 at 11:34:21AM +0100, Thomas Zimmermann wrote:
>> Hi
>>
>> Am 03.02.21 um 11:29 schrieb Daniel Vetter:
>>> On Wed, Jan 27, 2021 at 03:05:03PM +0100, Thomas Zimmermann wrote:
>>>> Functions in the atomic commit tail are not allowed to acquire the
>>>> dmabuf's reservation lock. So we cannot legally call the GEM object's
>>>> vmap functionality in atomic_update.
>>>>
>>>> Instead vmap the cursor BO in prepare_fb and vunmap it in cleanup_fb.
>>>> The cursor plane state stores the mapping's address. The pinning of the
>>>> BO is implicitly done by vmap.
>>>>
>>>> As an extra benefit, there's no source of runtime errors left in
>>>> atomic_update.
>>>>
>>>> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
>>>
>>> Did you test this with my dma_fence_signalling annotations patches?
>>
>> Not with vbox. I did test similar code in my recent ast patchset. But I
>> think there's still a bug here, as there's no custom plane-reset function.
> 
> Do right, KASAN should complain when you load the driver because the first
> state is a bit too small. But probably still within the kmalloc'ed block
> by sheer luck. Worth confirming that KASAN can catch this.

I have KASAN enabled and I might just have missed the error message. I 
later saw the error with another driver after I already posted the vbox 
and ast patches.

If you have the time, a look at the first half of the ast patchset might 
still be worth it. It removes the cursor-code abstraction and shouldn't 
be affected by the issue.

Best regards
Thomas

> 
>>>
>>> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
>>
>> I'll certainly send out an updated patch.
> 
> I wonder whether it's worth to have a runtime check that when you
> overwrite one, you have to overwrite all of them or it's clearly buggy?
> -Daniel
> 
>>
>> Best regards
>> Thomas
>>
>>>
>>>> ---
>>>>    drivers/gpu/drm/vboxvideo/vbox_mode.c | 102 +++++++++++++++++++++-----
>>>>    1 file changed, 82 insertions(+), 20 deletions(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/vboxvideo/vbox_mode.c b/drivers/gpu/drm/vboxvideo/vbox_mode.c
>>>> index dbc0dd53c69e..b5625a7d6cef 100644
>>>> --- a/drivers/gpu/drm/vboxvideo/vbox_mode.c
>>>> +++ b/drivers/gpu/drm/vboxvideo/vbox_mode.c
>>>> @@ -324,6 +324,19 @@ static void vbox_primary_atomic_disable(struct drm_plane *plane,
>>>>    				    old_state->src_y >> 16);
>>>>    }
>>>> +struct vbox_cursor_plane_state {
>>>> +	struct drm_plane_state base;
>>>> +
>>>> +	/* Transitional state - do not export or duplicate */
>>>> +
>>>> +	struct dma_buf_map map;
>>>> +};
>>>> +
>>>> +static struct vbox_cursor_plane_state *to_vbox_cursor_plane_state(struct drm_plane_state *state)
>>>> +{
>>>> +	return container_of(state, struct vbox_cursor_plane_state, base);
>>>> +}
>>>> +
>>>>    static int vbox_cursor_atomic_check(struct drm_plane *plane,
>>>>    				    struct drm_plane_state *new_state)
>>>>    {
>>>> @@ -381,14 +394,13 @@ static void vbox_cursor_atomic_update(struct drm_plane *plane,
>>>>    		container_of(plane->dev, struct vbox_private, ddev);
>>>>    	struct vbox_crtc *vbox_crtc = to_vbox_crtc(plane->state->crtc);
>>>>    	struct drm_framebuffer *fb = plane->state->fb;
>>>> -	struct drm_gem_vram_object *gbo = drm_gem_vram_of_gem(fb->obj[0]);
>>>>    	u32 width = plane->state->crtc_w;
>>>>    	u32 height = plane->state->crtc_h;
>>>> +	struct vbox_cursor_plane_state *vbox_state = to_vbox_cursor_plane_state(plane->state);
>>>> +	struct dma_buf_map map = vbox_state->map;
>>>> +	u8 *src = map.vaddr; /* TODO: Use mapping abstraction properly */
>>>>    	size_t data_size, mask_size;
>>>>    	u32 flags;
>>>> -	struct dma_buf_map map;
>>>> -	int ret;
>>>> -	u8 *src;
>>>>    	/*
>>>>    	 * VirtualBox uses the host windowing system to draw the cursor so
>>>> @@ -401,17 +413,6 @@ static void vbox_cursor_atomic_update(struct drm_plane *plane,
>>>>    	vbox_crtc->cursor_enabled = true;
>>>> -	ret = drm_gem_vram_vmap(gbo, &map);
>>>> -	if (ret) {
>>>> -		/*
>>>> -		 * BUG: we should have pinned the BO in prepare_fb().
>>>> -		 */
>>>> -		mutex_unlock(&vbox->hw_mutex);
>>>> -		DRM_WARN("Could not map cursor bo, skipping update\n");
>>>> -		return;
>>>> -	}
>>>> -	src = map.vaddr; /* TODO: Use mapping abstraction properly */
>>>> -
>>>>    	/*
>>>>    	 * The mask must be calculated based on the alpha
>>>>    	 * channel, one bit per ARGB word, and must be 32-bit
>>>> @@ -421,7 +422,6 @@ static void vbox_cursor_atomic_update(struct drm_plane *plane,
>>>>    	data_size = width * height * 4 + mask_size;
>>>>    	copy_cursor_image(src, vbox->cursor_data, width, height, mask_size);
>>>> -	drm_gem_vram_vunmap(gbo, &map);
>>>>    	flags = VBOX_MOUSE_POINTER_VISIBLE | VBOX_MOUSE_POINTER_SHAPE |
>>>>    		VBOX_MOUSE_POINTER_ALPHA;
>>>> @@ -458,6 +458,43 @@ static void vbox_cursor_atomic_disable(struct drm_plane *plane,
>>>>    	mutex_unlock(&vbox->hw_mutex);
>>>>    }
>>>> +static int vbox_cursor_prepare_fb(struct drm_plane *plane, struct drm_plane_state *new_state)
>>>> +{
>>>> +	struct vbox_cursor_plane_state *new_vbox_state = to_vbox_cursor_plane_state(new_state);
>>>> +	struct drm_framebuffer *fb = new_state->fb;
>>>> +	struct drm_gem_vram_object *gbo;
>>>> +	struct dma_buf_map map;
>>>> +	int ret;
>>>> +
>>>> +	if (!fb)
>>>> +		return 0;
>>>> +
>>>> +	gbo = drm_gem_vram_of_gem(fb->obj[0]);
>>>> +
>>>> +	ret = drm_gem_vram_vmap(gbo, &map);
>>>> +	if (ret)
>>>> +		return ret;
>>>> +
>>>> +	new_vbox_state->map = map;
>>>> +
>>>> +	return 0;
>>>> +}
>>>> +
>>>> +static void vbox_cursor_cleanup_fb(struct drm_plane *plane, struct drm_plane_state *old_state)
>>>> +{
>>>> +	struct vbox_cursor_plane_state *old_vbox_state = to_vbox_cursor_plane_state(old_state);
>>>> +	struct drm_framebuffer *fb = old_state->fb;
>>>> +	struct dma_buf_map map = old_vbox_state->map;
>>>> +	struct drm_gem_vram_object *gbo;
>>>> +
>>>> +	if (!fb)
>>>> +		return;
>>>> +
>>>> +	gbo = drm_gem_vram_of_gem(fb->obj[0]);
>>>> +
>>>> +	drm_gem_vram_vunmap(gbo, &map);
>>>> +}
>>>> +
>>>>    static const u32 vbox_cursor_plane_formats[] = {
>>>>    	DRM_FORMAT_ARGB8888,
>>>>    };
>>>> @@ -466,17 +503,42 @@ static const struct drm_plane_helper_funcs vbox_cursor_helper_funcs = {
>>>>    	.atomic_check	= vbox_cursor_atomic_check,
>>>>    	.atomic_update	= vbox_cursor_atomic_update,
>>>>    	.atomic_disable	= vbox_cursor_atomic_disable,
>>>> -	.prepare_fb	= drm_gem_vram_plane_helper_prepare_fb,
>>>> -	.cleanup_fb	= drm_gem_vram_plane_helper_cleanup_fb,
>>>> +	.prepare_fb	= vbox_cursor_prepare_fb,
>>>> +	.cleanup_fb	= vbox_cursor_cleanup_fb,
>>>>    };
>>>> +static struct drm_plane_state *vbox_cursor_atomic_duplicate_state(struct drm_plane *plane)
>>>> +{
>>>> +	struct vbox_cursor_plane_state *new_vbox_state;
>>>> +	struct drm_device *dev = plane->dev;
>>>> +
>>>> +	if (drm_WARN_ON(dev, !plane->state))
>>>> +		return NULL;
>>>> +
>>>> +	new_vbox_state = kzalloc(sizeof(*new_vbox_state), GFP_KERNEL);
>>>> +	if (!new_vbox_state)
>>>> +		return NULL;
>>>> +	__drm_atomic_helper_plane_duplicate_state(plane, &new_vbox_state->base);
>>>> +
>>>> +	return &new_vbox_state->base;
>>>> +}
>>>> +
>>>> +static void vbox_cursor_atomic_destroy_state(struct drm_plane *plane,
>>>> +					     struct drm_plane_state *state)
>>>> +{
>>>> +	struct vbox_cursor_plane_state *vbox_state = to_vbox_cursor_plane_state(state);
>>>> +
>>>> +	__drm_atomic_helper_plane_destroy_state(&vbox_state->base);
>>>> +	kfree(vbox_state);
>>>> +}
>>>> +
>>>>    static const struct drm_plane_funcs vbox_cursor_plane_funcs = {
>>>>    	.update_plane	= drm_atomic_helper_update_plane,
>>>>    	.disable_plane	= drm_atomic_helper_disable_plane,
>>>>    	.destroy	= drm_primary_helper_destroy,
>>>>    	.reset		= drm_atomic_helper_plane_reset,
>>>> -	.atomic_duplicate_state = drm_atomic_helper_plane_duplicate_state,
>>>> -	.atomic_destroy_state = drm_atomic_helper_plane_destroy_state,
>>>> +	.atomic_duplicate_state = vbox_cursor_atomic_duplicate_state,
>>>> +	.atomic_destroy_state = vbox_cursor_atomic_destroy_state,
>>>>    };
>>>>    static const u32 vbox_primary_plane_formats[] = {
>>>>
>>>> base-commit: 3836b7fdfad40e2bac5dc882332f42bed6942cf4
>>>> prerequisite-patch-id: c2b2f08f0eccc9f5df0c0da49fa1d36267deb11d
>>>> -- 
>>>> 2.30.0
>>>>
>>>
>>
>> -- 
>> Thomas Zimmermann
>> Graphics Driver Developer
>> SUSE Software Solutions Germany GmbH
>> Maxfeldstr. 5, 90409 Nürnberg, Germany
>> (HRB 36809, AG Nürnberg)
>> Geschäftsführer: Felix Imendörffer
>>
> 
> 
> 
> 

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Felix Imendörffer


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