[Public]

Thanks, Lyude.

Feel free to add Reviewed-by: Wayne Lin Wayne.Lin@amd.com

-----Original Message----- From: Lyude Paul lyude@redhat.com Sent: Friday, June 3, 2022 4:18 AM To: dri-devel@lists.freedesktop.org Cc: David Airlie airlied@linux.ie; Daniel Vetter daniel@ffwll.ch; Thomas Zimmermann tzimmermann@suse.de; Lin, Wayne Wayne.Lin@amd.com; Jani Nikula jani.nikula@intel.com; Lakha, Bhawanpreet Bhawanpreet.Lakha@amd.com; Rajkumar Subbiah rsubbia@codeaurora.org; open list linux-kernel@vger.kernel.org Subject: [PATCH 1/3] drm/display/dp_mst: Don't validate port refs in drm_dp_check_and_send_link_address()

Drive-by cleanup, we don't need to validate the port references here as we already previously went through the effort of refactoring things such that we're guaranteed to be able to access ->mstb and ->port safely from drm_dp_check_and_send_link_address(), since the only two places in the codebase that drop an MST reference in such a way that it would remove it from the topology are both protected under probe_lock.

Thanks for that, past Lyude!

Signed-off-by: Lyude Paul lyude@redhat.com

drivers/gpu/drm/display/drm_dp_mst_topology.c | 22 +++++-------------- 1 file changed, 6 insertions(+), 16 deletions(-)

diff --git a/drivers/gpu/drm/display/drm_dp_mst_topology.c b/drivers/gpu/drm/display/drm_dp_mst_topology.c index 67b3b9697da7..d84673b3294b 100644 --- a/drivers/gpu/drm/display/drm_dp_mst_topology.c +++ b/drivers/gpu/drm/display/drm_dp_mst_topology.c @@ -2666,24 +2666,14 @@ static int drm_dp_check_and_send_link_address(struct drm_dp_mst_topology_mgr *mg }

list_for_each_entry(port, &mstb->ports, next) {

• struct drm_dp_mst_branch *mstb_child = NULL;
  

• if (port->input || !port->ddps)
  

• if (port->input || !port->ddps || !port->mstb)
  continue;
  
  

• if (port->mstb)
  

• 	mstb_child =
  

drm_dp_mst_topology_get_mstb_validated(

• 	    mgr, port->mstb);
  

• if (mstb_child) {
  

• 	ret = drm_dp_check_and_send_link_address(mgr,
  

• 						 mstb_child);
  

• 	drm_dp_mst_topology_put_mstb(mstb_child);
  

• 	if (ret == 1)
  

• 		changed = true;
  

• 	else if (ret < 0)
  

• 		return ret;
  

• }
  

• ret = drm_dp_check_and_send_link_address(mgr, port-
  

...

mstb);

• if (ret == 1)
  

• 	changed = true;
  

• else if (ret < 0)
  

• 	return ret;
  

  }

  return changed;

-- 2.35.3

-- Regards, Wayne

On Thu, Jun 02, 2022 at 04:17:56PM -0400, Lyude Paul wrote:

I noticed a rather surprising issue here while working on removing all of the non-atomic MST code: drm_atomic_get_mst_topology_state() doesn't check the return value of drm_atomic_get_private_obj_state() and instead just passes it directly to to_dp_mst_topology_state(). This means that if we hit a deadlock or something else which would return an error code pointer, we'll likely segfault the kernel.

This is definitely another one of those fixes where I'm astonished we somehow managed never to discover this issue until now…

It has been discussed before.

struct drm_dp_mst_topology_state { struct drm_private_state base; ... }

so offsetof(base)==0.

Signed-off-by: Lyude Paul lyude@redhat.com Fixes: a4370c777406 ("drm/atomic: Make private objs proper objects") Cc: Ville Syrjälä ville.syrjala@linux.intel.com Cc: stable@vger.kernel.org # v4.14+

---

drivers/gpu/drm/display/drm_dp_mst_topology.c | 2 +- include/drm/display/drm_dp_mst_helper.h | 2 ++ 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/display/drm_dp_mst_topology.c b/drivers/gpu/drm/display/drm_dp_mst_topology.c index d84673b3294b..d6e595b95f07 100644 --- a/drivers/gpu/drm/display/drm_dp_mst_topology.c +++ b/drivers/gpu/drm/display/drm_dp_mst_topology.c @@ -5468,7 +5468,7 @@ EXPORT_SYMBOL(drm_dp_mst_topology_state_funcs); struct drm_dp_mst_topology_state *drm_atomic_get_mst_topology_state(struct drm_atomic_state *state, struct drm_dp_mst_topology_mgr *mgr) {

• return to_dp_mst_topology_state(drm_atomic_get_private_obj_state(state, &mgr->base));

• return to_dp_mst_topology_state_safe(drm_atomic_get_private_obj_state(state, &mgr->base));

} EXPORT_SYMBOL(drm_atomic_get_mst_topology_state);

diff --git a/include/drm/display/drm_dp_mst_helper.h b/include/drm/display/drm_dp_mst_helper.h index 10adec068b7f..fe7577e7f305 100644 --- a/include/drm/display/drm_dp_mst_helper.h +++ b/include/drm/display/drm_dp_mst_helper.h @@ -541,6 +541,8 @@ struct drm_dp_payload { };

#define to_dp_mst_topology_state(x) container_of(x, struct drm_dp_mst_topology_state, base) +#define to_dp_mst_topology_state_safe(x) \

• container_of_safe(x, struct drm_dp_mst_topology_state, base)

Wasn't aware of container_of_safe(). I suppose no real harm in using it. Not sure why we'd even keep the non-safe version around?

Though the use of container_of_safe() everywhere won't help when "casting" the other way (&foo->base, when foo==NULL/errptr). In order to make that work for non-zero offsets we'd have to introduce a casting macro for that direction as well.

struct drm_dp_vcpi_allocation { struct drm_dp_mst_port *port; -- 2.35.3

Thanks! Will push these two patches upstream

On Mon, 2022-06-13 at 09:59 +0000, Lin, Wayne wrote:

[Public]

Hi Lyude,

Feel free to add Reviewed-by: Wayne Lin Wayne.Lin@amd.com

...

-----Original Message----- From: Lyude Paul lyude@redhat.com Sent: Friday, June 3, 2022 4:18 AM To: dri-devel@lists.freedesktop.org Cc: David Airlie airlied@linux.ie; Daniel Vetter daniel@ffwll.ch; Thomas Zimmermann tzimmermann@suse.de; Lin, Wayne Wayne.Lin@amd.com; Jani Nikula jani.nikula@intel.com; Lakha, Bhawanpreet Bhawanpreet.Lakha@amd.com; Rajkumar Subbiah rsubbia@codeaurora.org; open list linux-kernel@vger.kernel.org Subject: [PATCH 3/3] drm/dp_mst: Get rid of old comment in drm_atomic_get_mst_topology_state docs

We don't actually care about connection_mutex here anymore, so let's get rid of the comment mentioning it in this function's kdocs.

Signed-off-by: Lyude Paul lyude@redhat.com

drivers/gpu/drm/display/drm_dp_mst_topology.c | 3 +--  1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/display/drm_dp_mst_topology.c b/drivers/gpu/drm/display/drm_dp_mst_topology.c index d6e595b95f07..9f96132a5d74 100644 --- a/drivers/gpu/drm/display/drm_dp_mst_topology.c +++ b/drivers/gpu/drm/display/drm_dp_mst_topology.c @@ -5458,8 +5458,7 @@ EXPORT_SYMBOL(drm_dp_mst_topology_state_funcs);   *   * This function wraps drm_atomic_get_priv_obj_state() passing in the MST atomic   * state vtable so that the private object state returned is that of a MST

• • topology object. Also, drm_atomic_get_private_obj_state() expects the

caller

• • to care of the locking, so warn if don't hold the connection_mutex.

• • topology object.

*   * RETURNS:   * -- 2.35.3

-- Regards, Wayne Lin