Re: [PATCH] drm/qxl: Pin buffer objects for internal mappings

[Daniel Vetter <daniel.vetter@ffwll.ch>]

On Mon, Jul 08, 2024 at 10:09:44AM +0200, Thomas Zimmermann wrote:
> Hi,
> 
> ping for a review. This is a bugfix for a serious problem.

I tried to look around whether there's any place where we could WARN_ON if
we create a vmap but it's not pinned. But there's lots of places where we
want the vmap only for the duration of the dma_resv locked section, so
really can't do that. And your patch removes the unlocked vmap
implementation, which would be the only place really.

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

> 
> Best regards
> Thomas
> 
> Am 02.07.24 um 16:20 schrieb Thomas Zimmermann:
> > Add qxl_bo_pin_and_vmap() that pins and vmaps a buffer object in one
> > step. Update callers of the regular qxl_bo_vmap(). Fixes a bug where
> > qxl accesses an unpinned buffer object while it is being moved; such
> > as with the monitor-description BO. An typical error is shown below.
> > 
> > [    4.303586] [drm:drm_atomic_helper_commit_planes] *ERROR* head 1 wrong: 65376256x16777216+0+0
> > [    4.586883] [drm:drm_atomic_helper_commit_planes] *ERROR* head 1 wrong: 65376256x16777216+0+0
> > [    4.904036] [drm:drm_atomic_helper_commit_planes] *ERROR* head 1 wrong: 65335296x16777216+0+0
> > [    5.374347] [drm:qxl_release_from_id_locked] *ERROR* failed to find id in release_idr
> > 
> > Commit b33651a5c98d ("drm/qxl: Do not pin buffer objects for vmap")
> > removed the implicit pin operation from qxl's vmap code. This is the
> > correct behavior for GEM and PRIME interfaces, but the pin is still
> > needed for qxl internal operation.
> > 
> > Also add a corresponding function qxl_bo_vunmap_and_unpin() and remove
> > the old qxl_bo_vmap() helpers.
> > 
> > Future directions: BOs should not be pinned or vmapped unnecessarily.
> > The pin-and-vmap operation should be removed from the driver and a
> > temporary mapping should be established with a vmap_local-like helper.
> > See the client helper drm_client_buffer_vmap_local() for semantics.
> > 
> > Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
> > Fixes: b33651a5c98d ("drm/qxl: Do not pin buffer objects for vmap")
> > Reported-by: David Kaplan <david.kaplan@amd.com>
> > Closes: https://lore.kernel.org/dri-devel/ab0fb17d-0f96-4ee6-8b21-65d02bb02655@suse.de/
> > Tested-by: David Kaplan <david.kaplan@amd.com>
> > Cc: Thomas Zimmermann <tzimmermann@suse.de>
> > Cc: Dmitry Osipenko <dmitry.osipenko@collabora.com>
> > Cc: Christian König <christian.koenig@amd.com>
> > Cc: Zack Rusin <zack.rusin@broadcom.com>
> > Cc: Dave Airlie <airlied@redhat.com>
> > Cc: Gerd Hoffmann <kraxel@redhat.com>
> > Cc: virtualization@lists.linux.dev
> > Cc: spice-devel@lists.freedesktop.org
> > ---
> >   drivers/gpu/drm/qxl/qxl_display.c | 14 +++++++-------
> >   drivers/gpu/drm/qxl/qxl_object.c  | 11 +++++++++--
> >   drivers/gpu/drm/qxl/qxl_object.h  |  4 ++--
> >   3 files changed, 18 insertions(+), 11 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/qxl/qxl_display.c b/drivers/gpu/drm/qxl/qxl_display.c
> > index 86a5dea710c0..bc24af08dfcd 100644
> > --- a/drivers/gpu/drm/qxl/qxl_display.c
> > +++ b/drivers/gpu/drm/qxl/qxl_display.c
> > @@ -584,11 +584,11 @@ static struct qxl_bo *qxl_create_cursor(struct qxl_device *qdev,
> >   	if (ret)
> >   		goto err;
> > -	ret = qxl_bo_vmap(cursor_bo, &cursor_map);
> > +	ret = qxl_bo_pin_and_vmap(cursor_bo, &cursor_map);
> >   	if (ret)
> >   		goto err_unref;
> > -	ret = qxl_bo_vmap(user_bo, &user_map);
> > +	ret = qxl_bo_pin_and_vmap(user_bo, &user_map);
> >   	if (ret)
> >   		goto err_unmap;
> > @@ -614,12 +614,12 @@ static struct qxl_bo *qxl_create_cursor(struct qxl_device *qdev,
> >   		       user_map.vaddr, size);
> >   	}
> > -	qxl_bo_vunmap(user_bo);
> > -	qxl_bo_vunmap(cursor_bo);
> > +	qxl_bo_vunmap_and_unpin(user_bo);
> > +	qxl_bo_vunmap_and_unpin(cursor_bo);
> >   	return cursor_bo;
> >   err_unmap:
> > -	qxl_bo_vunmap(cursor_bo);
> > +	qxl_bo_vunmap_and_unpin(cursor_bo);
> >   err_unref:
> >   	qxl_bo_unpin(cursor_bo);
> >   	qxl_bo_unref(&cursor_bo);
> > @@ -1205,7 +1205,7 @@ int qxl_create_monitors_object(struct qxl_device *qdev)
> >   	}
> >   	qdev->monitors_config_bo = gem_to_qxl_bo(gobj);
> > -	ret = qxl_bo_vmap(qdev->monitors_config_bo, &map);
> > +	ret = qxl_bo_pin_and_vmap(qdev->monitors_config_bo, &map);
> >   	if (ret)
> >   		return ret;
> > @@ -1236,7 +1236,7 @@ int qxl_destroy_monitors_object(struct qxl_device *qdev)
> >   	qdev->monitors_config = NULL;
> >   	qdev->ram_header->monitors_config = 0;
> > -	ret = qxl_bo_vunmap(qdev->monitors_config_bo);
> > +	ret = qxl_bo_vunmap_and_unpin(qdev->monitors_config_bo);
> >   	if (ret)
> >   		return ret;
> > diff --git a/drivers/gpu/drm/qxl/qxl_object.c b/drivers/gpu/drm/qxl/qxl_object.c
> > index 5893e27a7ae5..cb1b7c2580ae 100644
> > --- a/drivers/gpu/drm/qxl/qxl_object.c
> > +++ b/drivers/gpu/drm/qxl/qxl_object.c
> > @@ -182,7 +182,7 @@ int qxl_bo_vmap_locked(struct qxl_bo *bo, struct iosys_map *map)
> >   	return 0;
> >   }
> > -int qxl_bo_vmap(struct qxl_bo *bo, struct iosys_map *map)
> > +int qxl_bo_pin_and_vmap(struct qxl_bo *bo, struct iosys_map *map)
> >   {
> >   	int r;
> > @@ -190,7 +190,13 @@ int qxl_bo_vmap(struct qxl_bo *bo, struct iosys_map *map)
> >   	if (r)
> >   		return r;
> > +	r = qxl_bo_pin_locked(bo);
> > +	if (r)
> > +		return r;
> > +
> >   	r = qxl_bo_vmap_locked(bo, map);
> > +	if (r)
> > +		qxl_bo_unpin_locked(bo);
> >   	qxl_bo_unreserve(bo);
> >   	return r;
> >   }
> > @@ -241,7 +247,7 @@ void qxl_bo_vunmap_locked(struct qxl_bo *bo)
> >   	ttm_bo_vunmap(&bo->tbo, &bo->map);
> >   }
> > -int qxl_bo_vunmap(struct qxl_bo *bo)
> > +int qxl_bo_vunmap_and_unpin(struct qxl_bo *bo)
> >   {
> >   	int r;
> > @@ -250,6 +256,7 @@ int qxl_bo_vunmap(struct qxl_bo *bo)
> >   		return r;
> >   	qxl_bo_vunmap_locked(bo);
> > +	qxl_bo_unpin_locked(bo);
> >   	qxl_bo_unreserve(bo);
> >   	return 0;
> >   }
> > diff --git a/drivers/gpu/drm/qxl/qxl_object.h b/drivers/gpu/drm/qxl/qxl_object.h
> > index 1cf5bc759101..875f63221074 100644
> > --- a/drivers/gpu/drm/qxl/qxl_object.h
> > +++ b/drivers/gpu/drm/qxl/qxl_object.h
> > @@ -59,9 +59,9 @@ extern int qxl_bo_create(struct qxl_device *qdev,
> >   			 u32 priority,
> >   			 struct qxl_surface *surf,
> >   			 struct qxl_bo **bo_ptr);
> > -int qxl_bo_vmap(struct qxl_bo *bo, struct iosys_map *map);
> > +int qxl_bo_pin_and_vmap(struct qxl_bo *bo, struct iosys_map *map);
> >   int qxl_bo_vmap_locked(struct qxl_bo *bo, struct iosys_map *map);
> > -int qxl_bo_vunmap(struct qxl_bo *bo);
> > +int qxl_bo_vunmap_and_unpin(struct qxl_bo *bo);
> >   void qxl_bo_vunmap_locked(struct qxl_bo *bo);
> >   void *qxl_bo_kmap_atomic_page(struct qxl_device *qdev, struct qxl_bo *bo, int page_offset);
> >   void qxl_bo_kunmap_atomic_page(struct qxl_device *qdev, struct qxl_bo *bo, void *map);
> 
> -- 
> --
> Thomas Zimmermann
> Graphics Driver Developer
> SUSE Software Solutions Germany GmbH
> Frankenstrasse 146, 90461 Nuernberg, Germany
> GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
> HRB 36809 (AG Nuernberg)
> 

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