Re: [PATCH v3 6/8] drm/shmem-helper: Provide a vmap function for short-term mappings

[Thomas Zimmermann <tzimmermann@xxxxxxx>]

Hi Daniel

Am 11.12.20 um 10:50 schrieb Daniel Vetter:
[...]
> > +/**
> > + * drm_gem_shmem_vmap_local - Create a virtual mapping for a shmem GEM object
> > + * @shmem: shmem GEM object
> > + * @map: Returns the kernel virtual address of the SHMEM GEM object's backing
> > + *       store.
> > + *
> > + * This function makes sure that a contiguous kernel virtual address mapping
> > + * exists for the buffer backing the shmem GEM object.
> > + *
> > + * The function is called with the BO's reservation object locked. Callers must
> > + * hold the lock until after unmapping the buffer.
> > + *
> > + * This function can be used to implement &drm_gem_object_funcs.vmap_local. But
> > + * it can also be called by drivers directly, in which case it will hide the
> > + * differences between dma-buf imported and natively allocated objects.
> > + *
> > + * Acquired mappings should be cleaned up by calling drm_gem_shmem_vunmap_local().
> > + *
> > + * Returns:
> > + * 0 on success or a negative error code on failure.
> > + */
> > +int drm_gem_shmem_vmap_local(struct drm_gem_object *obj, struct dma_buf_map *map)
> > +{
> > +	struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);
> > +	int ret;
> > +
> > +	dma_resv_assert_held(obj->resv);
> > +
> > +	ret = mutex_lock_interruptible(&shmem->vmap_lock);
>
> This bites. You need to check for shmem->import_attach and call
> dma_buf_vmap_local directly here before you take any shmem helper locks.
> Real fix would be to replace both vmap_lock and pages_lock with dma_resv
> lock, but that's more work. Same for vunmap_local

This comment confuses me. AFAICT vmap_lock protects vmap_use_count. Why 
does this exact code work in drm_gem_shmem_vmap() but not in _local() ?

Best regards
Thomas

> With that fixed on the helper part of this patch:
>
> Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
>
>
> > +	if (ret)
> > +		return ret;
> > +	ret = drm_gem_shmem_vmap_locked(shmem, map);
> > +	mutex_unlock(&shmem->vmap_lock);
> > +
> > +	return ret;
> > +}
> > +EXPORT_SYMBOL(drm_gem_shmem_vmap_local);
> > +
> >   static void drm_gem_shmem_vunmap_locked(struct drm_gem_shmem_object *shmem,
> >   					struct dma_buf_map *map)
> >   {
> > @@ -366,7 +406,7 @@ static void drm_gem_shmem_vunmap_locked(struct drm_gem_shmem_object *shmem,
> >   	drm_gem_shmem_put_pages(shmem);
> >   }
> >   
> > -/*
> > +/**
> >    * drm_gem_shmem_vunmap - Unmap a virtual mapping fo a shmem GEM object
> >    * @shmem: shmem GEM object
> >    * @map: Kernel virtual address where the SHMEM GEM object was mapped
> > @@ -389,6 +429,33 @@ void drm_gem_shmem_vunmap(struct drm_gem_object *obj, struct dma_buf_map *map)
> >   }
> >   EXPORT_SYMBOL(drm_gem_shmem_vunmap);
> >   
> > +/**
> > + * drm_gem_shmem_vunmap_local - Unmap a virtual mapping fo a shmem GEM object
> > + * @shmem: shmem GEM object
> > + * @map: Kernel virtual address where the SHMEM GEM object was mapped
> > + *
> > + * This function cleans up a kernel virtual address mapping acquired by
> > + * drm_gem_shmem_vmap_local(). The mapping is only removed when the use count
> > + * drops to zero.
> > + *
> > + * The function is called with the BO's reservation object locked.
> > + *
> > + * This function can be used to implement &drm_gem_object_funcs.vmap_local.
> > + * But it can also be called by drivers directly, in which case it will hide
> > + * the differences between dma-buf imported and natively allocated objects.
> > + */
> > +void drm_gem_shmem_vunmap_local(struct drm_gem_object *obj, struct dma_buf_map *map)
> > +{
> > +	struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);
> > +
> > +	dma_resv_assert_held(obj->resv);
> > +
> > +	mutex_lock(&shmem->vmap_lock);
> > +	drm_gem_shmem_vunmap_locked(shmem, map);
> > +	mutex_unlock(&shmem->vmap_lock);
> > +}
> > +EXPORT_SYMBOL(drm_gem_shmem_vunmap_local);
> > +
> >   struct drm_gem_shmem_object *
> >   drm_gem_shmem_create_with_handle(struct drm_file *file_priv,
> >   				 struct drm_device *dev, size_t size,
> > diff --git a/drivers/gpu/drm/mgag200/mgag200_mode.c b/drivers/gpu/drm/mgag200/mgag200_mode.c
> > index 1dfc42170059..a33e28d4c5e9 100644
> > --- a/drivers/gpu/drm/mgag200/mgag200_mode.c
> > +++ b/drivers/gpu/drm/mgag200/mgag200_mode.c
> > @@ -1552,22 +1552,32 @@ mgag200_handle_damage(struct mga_device *mdev, struct drm_framebuffer *fb,
> >   		      struct drm_rect *clip)
> >   {
> >   	struct drm_device *dev = &mdev->base;
> > +	struct drm_gem_object *obj = fb->obj[0];
> >   	struct dma_buf_map map;
> >   	void *vmap;
> >   	int ret;
> >   
> > -	ret = drm_gem_shmem_vmap(fb->obj[0], &map);
> > +	ret = dma_resv_lock(obj->resv, NULL);
> >   	if (drm_WARN_ON(dev, ret))
> > -		return; /* BUG: SHMEM BO should always be vmapped */
> > +		return;
> > +	ret = drm_gem_shmem_vmap_local(obj, &map);
> > +	if (drm_WARN_ON(dev, ret))
> > +		goto err_dma_resv_unlock; /* BUG: SHMEM BO should always be vmapped */
> >   	vmap = map.vaddr; /* TODO: Use mapping abstraction properly */
> >   
> >   	drm_fb_memcpy_dstclip(mdev->vram, vmap, fb, clip);
> >   
> > -	drm_gem_shmem_vunmap(fb->obj[0], &map);
> > +	drm_gem_shmem_vunmap_local(obj, &map);
> > +	dma_resv_unlock(obj->resv);
> >   
> >   	/* Always scanout image at VRAM offset 0 */
> >   	mgag200_set_startadd(mdev, (u32)0);
> >   	mgag200_set_offset(mdev, fb);
> > +
> > +	return;
> > +
> > +err_dma_resv_unlock:
> > +	dma_resv_unlock(obj->resv);
> >   }
> >   
> >   static void
> > diff --git a/drivers/gpu/drm/tiny/cirrus.c b/drivers/gpu/drm/tiny/cirrus.c
> > index 561c49d8657a..58c694964148 100644
> > --- a/drivers/gpu/drm/tiny/cirrus.c
> > +++ b/drivers/gpu/drm/tiny/cirrus.c
> > @@ -315,6 +315,7 @@ static int cirrus_fb_blit_rect(struct drm_framebuffer *fb,
> >   			       struct drm_rect *rect)
> >   {
> >   	struct cirrus_device *cirrus = to_cirrus(fb->dev);
> > +	struct drm_gem_object *obj = fb->obj[0];
> >   	struct dma_buf_map map;
> >   	void *vmap;
> >   	int idx, ret;
> > @@ -323,9 +324,12 @@ static int cirrus_fb_blit_rect(struct drm_framebuffer *fb,
> >   	if (!drm_dev_enter(&cirrus->dev, &idx))
> >   		goto out;
> >   
> > -	ret = drm_gem_shmem_vmap(fb->obj[0], &map);
> > +	ret = dma_resv_lock(obj->resv, NULL);
> >   	if (ret)
> >   		goto out_dev_exit;
> > +	ret = drm_gem_shmem_vmap_local(fb->obj[0], &map);
> > +	if (ret)
> > +		goto out_dma_resv_unlock;
> >   	vmap = map.vaddr; /* TODO: Use mapping abstraction properly */
> >   
> >   	if (cirrus->cpp == fb->format->cpp[0])
> > @@ -345,9 +349,11 @@ static int cirrus_fb_blit_rect(struct drm_framebuffer *fb,
> >   	else
> >   		WARN_ON_ONCE("cpp mismatch");
> >   
> > -	drm_gem_shmem_vunmap(fb->obj[0], &map);
> >   	ret = 0;
> >   
> > +	drm_gem_shmem_vunmap_local(obj, &map);
> > +out_dma_resv_unlock:
> > +	dma_resv_unlock(obj->resv);
> >   out_dev_exit:
> >   	drm_dev_exit(idx);
> >   out:
> > diff --git a/drivers/gpu/drm/tiny/gm12u320.c b/drivers/gpu/drm/tiny/gm12u320.c
> > index 33f65f4626e5..b0c6e350f2b3 100644
> > --- a/drivers/gpu/drm/tiny/gm12u320.c
> > +++ b/drivers/gpu/drm/tiny/gm12u320.c
> > @@ -265,11 +265,16 @@ static void gm12u320_copy_fb_to_blocks(struct gm12u320_device *gm12u320)
> >   	y1 = gm12u320->fb_update.rect.y1;
> >   	y2 = gm12u320->fb_update.rect.y2;
> >   
> > -	ret = drm_gem_shmem_vmap(fb->obj[0], &map);
> > +	ret = dma_resv_lock(fb->obj[0]->resv, NULL);
> >   	if (ret) {
> > -		GM12U320_ERR("failed to vmap fb: %d\n", ret);
> > +		GM12U320_ERR("failed to reserve fb: %d\n", ret);
> >   		goto put_fb;
> >   	}
> > +	ret = drm_gem_shmem_vmap_local(fb->obj[0], &map);
> > +	if (ret) {
> > +		GM12U320_ERR("failed to vmap fb: %d\n", ret);
> > +		goto unlock_resv;
> > +	}
> >   	vaddr = map.vaddr; /* TODO: Use mapping abstraction properly */
> >   
> >   	if (fb->obj[0]->import_attach) {
> > @@ -321,8 +326,11 @@ static void gm12u320_copy_fb_to_blocks(struct gm12u320_device *gm12u320)
> >   		if (ret)
> >   			GM12U320_ERR("dma_buf_end_cpu_access err: %d\n", ret);
> >   	}
> > +
> > +unlock_resv:
> > +	dma_resv_unlock(fb->obj[0]->resv);
> >   vunmap:
> > -	drm_gem_shmem_vunmap(fb->obj[0], &map);
> > +	drm_gem_shmem_vunmap_local(fb->obj[0], &map);
> >   put_fb:
> >   	drm_framebuffer_put(fb);
> >   	gm12u320->fb_update.fb = NULL;
> > diff --git a/drivers/gpu/drm/udl/udl_modeset.c b/drivers/gpu/drm/udl/udl_modeset.c
> > index 9d34ec9d03f6..46b55b4d03c2 100644
> > --- a/drivers/gpu/drm/udl/udl_modeset.c
> > +++ b/drivers/gpu/drm/udl/udl_modeset.c
> > @@ -290,14 +290,18 @@ static int udl_handle_damage(struct drm_framebuffer *fb, int x, int y,
> >   	else if ((clip.x2 > fb->width) || (clip.y2 > fb->height))
> >   		return -EINVAL;
> >   
> > +	ret = dma_resv_lock(fb->obj[0]->resv, NULL);
> > +	if (ret)
> > +		return ret;
> > +
> >   	if (import_attach) {
> >   		ret = dma_buf_begin_cpu_access(import_attach->dmabuf,
> >   					       DMA_FROM_DEVICE);
> >   		if (ret)
> > -			return ret;
> > +			goto out_dma_resv_unlock;
> >   	}
> >   
> > -	ret = drm_gem_shmem_vmap(fb->obj[0], &map);
> > +	ret = drm_gem_shmem_vmap_local(fb->obj[0], &map);
> >   	if (ret) {
> >   		DRM_ERROR("failed to vmap fb\n");
> >   		goto out_dma_buf_end_cpu_access;
> > @@ -307,7 +311,7 @@ static int udl_handle_damage(struct drm_framebuffer *fb, int x, int y,
> >   	urb = udl_get_urb(dev);
> >   	if (!urb) {
> >   		ret = -ENOMEM;
> > -		goto out_drm_gem_shmem_vunmap;
> > +		goto out_drm_gem_shmem_vunmap_local;
> >   	}
> >   	cmd = urb->transfer_buffer;
> >   
> > @@ -320,7 +324,7 @@ static int udl_handle_damage(struct drm_framebuffer *fb, int x, int y,
> >   				       &cmd, byte_offset, dev_byte_offset,
> >   				       byte_width);
> >   		if (ret)
> > -			goto out_drm_gem_shmem_vunmap;
> > +			goto out_drm_gem_shmem_vunmap_local;
> >   	}
> >   
> >   	if (cmd > (char *)urb->transfer_buffer) {
> > @@ -336,8 +340,8 @@ static int udl_handle_damage(struct drm_framebuffer *fb, int x, int y,
> >   
> >   	ret = 0;
> >   
> > -out_drm_gem_shmem_vunmap:
> > -	drm_gem_shmem_vunmap(fb->obj[0], &map);
> > +out_drm_gem_shmem_vunmap_local:
> > +	drm_gem_shmem_vunmap_local(fb->obj[0], &map);
> >   out_dma_buf_end_cpu_access:
> >   	if (import_attach) {
> >   		tmp_ret = dma_buf_end_cpu_access(import_attach->dmabuf,
> > @@ -345,6 +349,8 @@ static int udl_handle_damage(struct drm_framebuffer *fb, int x, int y,
> >   		if (tmp_ret && !ret)
> >   			ret = tmp_ret; /* only update ret if not set yet */
> >   	}
> > +out_dma_resv_unlock:
> > +	dma_resv_unlock(fb->obj[0]->resv);
> >   
> >   	return ret;
> >   }
> > diff --git a/include/drm/drm_gem_shmem_helper.h b/include/drm/drm_gem_shmem_helper.h
> > index 434328d8a0d9..3f59bdf749aa 100644
> > --- a/include/drm/drm_gem_shmem_helper.h
> > +++ b/include/drm/drm_gem_shmem_helper.h
> > @@ -114,7 +114,9 @@ void drm_gem_shmem_put_pages(struct drm_gem_shmem_object *shmem);
> >   int drm_gem_shmem_pin(struct drm_gem_object *obj);
> >   void drm_gem_shmem_unpin(struct drm_gem_object *obj);
> >   int drm_gem_shmem_vmap(struct drm_gem_object *obj, struct dma_buf_map *map);
> > +int drm_gem_shmem_vmap_local(struct drm_gem_object *obj, struct dma_buf_map *map);
> >   void drm_gem_shmem_vunmap(struct drm_gem_object *obj, struct dma_buf_map *map);
> > +void drm_gem_shmem_vunmap_local(struct drm_gem_object *obj, struct dma_buf_map *map);
> >   
> >   int drm_gem_shmem_madvise(struct drm_gem_object *obj, int madv);
> >   
> > --
> > 2.29.2

--
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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