Re: [PATCH] drm/xen-front: Make shmem backed display buffer coherent

[Oleksandr Andrushchenko <andr2000@gmail.com>]

On 12/14/18 10:35 AM, Daniel Vetter wrote:
> On Fri, Dec 14, 2018 at 09:09:45AM +0200, Oleksandr Andrushchenko wrote:
>> On 12/13/18 5:48 PM, Daniel Vetter wrote:
>>> On Thu, Dec 13, 2018 at 12:17:54PM +0200, Oleksandr Andrushchenko wrote:
>>>> Daniel, could you please comment?
>>> Cross-revieweing someone else's stuff would scale better,
>> fair enough
>>>    I don't think
>>> I'll get around to anything before next year.
>> I put you on CC explicitly because you had comments on other patch [1]
>>
>> and this one tries to solve the issue raised (I tried to figure out
>>
>> at [2] if this is the way to go, but it seems I have no alternative here).
>>
>> While at it [3] (I hope) addresses your comments and the series just
>>
>> needs your single ack/nack to get in: all the rest ack/r-b are already
>>
>> there. Do you mind looking at it?
> As mentioned, much better if you aim for more per review with others, not
> just me. And all that dma coherency stuff isn't something a really
> understand all that well (I just know we have lots of pain). For options
> maybe work together with Gerd Hoffman or Noralf Tronnes, I think either
> has some patches pending that also need some review.

Fair enough,

thank you

> -Daniel
>
>>> -Daniel
>> Thank you very much for your time,
>>
>> Oleksandr
>>
>>>> Thank you
>>>>
>>>> On 11/27/18 12:32 PM, Oleksandr Andrushchenko wrote:
>>>>> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
>>>>>
>>>>> When GEM backing storage is allocated with drm_gem_get_pages
>>>>> the backing pages may be cached, thus making it possible that
>>>>> the backend sees only partial content of the buffer which may
>>>>> lead to screen artifacts. Make sure that the frontend's
>>>>> memory is coherent and the backend always sees correct display
>>>>> buffer content.
>>>>>
>>>>> Fixes: c575b7eeb89f ("drm/xen-front: Add support for Xen PV display frontend")
>>>>>
>>>>> Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
>>>>> ---
>>>>>     drivers/gpu/drm/xen/xen_drm_front_gem.c | 62 +++++++++++++++++++------
>>>>>     1 file changed, 48 insertions(+), 14 deletions(-)
>>>>>
>>>>> diff --git a/drivers/gpu/drm/xen/xen_drm_front_gem.c b/drivers/gpu/drm/xen/xen_drm_front_gem.c
>>>>> index 47ff019d3aef..c592735e49d2 100644
>>>>> --- a/drivers/gpu/drm/xen/xen_drm_front_gem.c
>>>>> +++ b/drivers/gpu/drm/xen/xen_drm_front_gem.c
>>>>> @@ -33,8 +33,11 @@ struct xen_gem_object {
>>>>>     	/* set for buffers allocated by the backend */
>>>>>     	bool be_alloc;
>>>>> -	/* this is for imported PRIME buffer */
>>>>> -	struct sg_table *sgt_imported;
>>>>> +	/*
>>>>> +	 * this is for imported PRIME buffer or the one allocated via
>>>>> +	 * drm_gem_get_pages.
>>>>> +	 */
>>>>> +	struct sg_table *sgt;
>>>>>     };
>>>>>     static inline struct xen_gem_object *
>>>>> @@ -77,10 +80,21 @@ static struct xen_gem_object *gem_create_obj(struct drm_device *dev,
>>>>>     	return xen_obj;
>>>>>     }
>>>>> +struct sg_table *xen_drm_front_gem_get_sg_table(struct drm_gem_object *gem_obj)
>>>>> +{
>>>>> +	struct xen_gem_object *xen_obj = to_xen_gem_obj(gem_obj);
>>>>> +
>>>>> +	if (!xen_obj->pages)
>>>>> +		return ERR_PTR(-ENOMEM);
>>>>> +
>>>>> +	return drm_prime_pages_to_sg(xen_obj->pages, xen_obj->num_pages);
>>>>> +}
>>>>> +
>>>>>     static struct xen_gem_object *gem_create(struct drm_device *dev, size_t size)
>>>>>     {
>>>>>     	struct xen_drm_front_drm_info *drm_info = dev->dev_private;
>>>>>     	struct xen_gem_object *xen_obj;
>>>>> +	struct address_space *mapping;
>>>>>     	int ret;
>>>>>     	size = round_up(size, PAGE_SIZE);
>>>>> @@ -113,10 +127,14 @@ static struct xen_gem_object *gem_create(struct drm_device *dev, size_t size)
>>>>>     		xen_obj->be_alloc = true;
>>>>>     		return xen_obj;
>>>>>     	}
>>>>> +
>>>>>     	/*
>>>>>     	 * need to allocate backing pages now, so we can share those
>>>>>     	 * with the backend
>>>>>     	 */
>>>>> +	mapping = xen_obj->base.filp->f_mapping;
>>>>> +	mapping_set_gfp_mask(mapping, GFP_USER | __GFP_DMA32);
>>>>> +
>>>>>     	xen_obj->num_pages = DIV_ROUND_UP(size, PAGE_SIZE);
>>>>>     	xen_obj->pages = drm_gem_get_pages(&xen_obj->base);
>>>>>     	if (IS_ERR_OR_NULL(xen_obj->pages)) {
>>>>> @@ -125,8 +143,27 @@ static struct xen_gem_object *gem_create(struct drm_device *dev, size_t size)
>>>>>     		goto fail;
>>>>>     	}
>>>>> +	xen_obj->sgt = xen_drm_front_gem_get_sg_table(&xen_obj->base);
>>>>> +	if (IS_ERR_OR_NULL(xen_obj->sgt)){
>>>>> +		ret = PTR_ERR(xen_obj->sgt);
>>>>> +		xen_obj->sgt = NULL;
>>>>> +		goto fail_put_pages;
>>>>> +	}
>>>>> +
>>>>> +	if (!dma_map_sg(dev->dev, xen_obj->sgt->sgl, xen_obj->sgt->nents,
>>>>> +			DMA_BIDIRECTIONAL)) {
>>>>> +		ret = -EFAULT;
>>>>> +		goto fail_free_sgt;
>>>>> +	}
>>>>> +
>>>>>     	return xen_obj;
>>>>> +fail_free_sgt:
>>>>> +	sg_free_table(xen_obj->sgt);
>>>>> +	xen_obj->sgt = NULL;
>>>>> +fail_put_pages:
>>>>> +	drm_gem_put_pages(&xen_obj->base, xen_obj->pages, true, false);
>>>>> +	xen_obj->pages = NULL;
>>>>>     fail:
>>>>>     	DRM_ERROR("Failed to allocate buffer with size %zu\n", size);
>>>>>     	return ERR_PTR(ret);
>>>>> @@ -149,7 +186,7 @@ void xen_drm_front_gem_free_object_unlocked(struct drm_gem_object *gem_obj)
>>>>>     	struct xen_gem_object *xen_obj = to_xen_gem_obj(gem_obj);
>>>>>     	if (xen_obj->base.import_attach) {
>>>>> -		drm_prime_gem_destroy(&xen_obj->base, xen_obj->sgt_imported);
>>>>> +		drm_prime_gem_destroy(&xen_obj->base, xen_obj->sgt);
>>>>>     		gem_free_pages_array(xen_obj);
>>>>>     	} else {
>>>>>     		if (xen_obj->pages) {
>>>>> @@ -158,6 +195,13 @@ void xen_drm_front_gem_free_object_unlocked(struct drm_gem_object *gem_obj)
>>>>>     							xen_obj->pages);
>>>>>     				gem_free_pages_array(xen_obj);
>>>>>     			} else {
>>>>> +				if (xen_obj->sgt) {
>>>>> +					dma_unmap_sg(xen_obj->base.dev->dev,
>>>>> +						     xen_obj->sgt->sgl,
>>>>> +						     xen_obj->sgt->nents,
>>>>> +						     DMA_BIDIRECTIONAL);
>>>>> +					sg_free_table(xen_obj->sgt);
>>>>> +				}
>>>>>     				drm_gem_put_pages(&xen_obj->base,
>>>>>     						  xen_obj->pages, true, false);
>>>>>     			}
>>>>> @@ -174,16 +218,6 @@ struct page **xen_drm_front_gem_get_pages(struct drm_gem_object *gem_obj)
>>>>>     	return xen_obj->pages;
>>>>>     }
>>>>> -struct sg_table *xen_drm_front_gem_get_sg_table(struct drm_gem_object *gem_obj)
>>>>> -{
>>>>> -	struct xen_gem_object *xen_obj = to_xen_gem_obj(gem_obj);
>>>>> -
>>>>> -	if (!xen_obj->pages)
>>>>> -		return ERR_PTR(-ENOMEM);
>>>>> -
>>>>> -	return drm_prime_pages_to_sg(xen_obj->pages, xen_obj->num_pages);
>>>>> -}
>>>>> -
>>>>>     struct drm_gem_object *
>>>>>     xen_drm_front_gem_import_sg_table(struct drm_device *dev,
>>>>>     				  struct dma_buf_attachment *attach,
>>>>> @@ -203,7 +237,7 @@ xen_drm_front_gem_import_sg_table(struct drm_device *dev,
>>>>>     	if (ret < 0)
>>>>>     		return ERR_PTR(ret);
>>>>> -	xen_obj->sgt_imported = sgt;
>>>>> +	xen_obj->sgt = sgt;
>>>>>     	ret = drm_prime_sg_to_page_addr_arrays(sgt, xen_obj->pages,
>>>>>     					       NULL, xen_obj->num_pages);
>>>> _______________________________________________
>>>> dri-devel mailing list
>>>> dri-devel@lists.freedesktop.org
>>>> https://lists.freedesktop.org/mailman/listinfo/dri-devel
>> [1] https://patchwork.kernel.org/patch/10693787/
>>
>> [2] https://lists.xen.org/archives/html/xen-devel/2018-11/msg02882.html
>>
>> [3] https://patchwork.kernel.org/patch/10705853/
>>
>>