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SubjectRe: [PATCH] drm/xen-front: Make shmem backed display buffer coherent
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, I don't think
I'll get around to anything before next year.
-Daniel

>
> 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

--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

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