Re: [PATCH v2 8/9] drm/fdinfo: Add comm/cmdline override fields

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 




In case you were waiting for me looking at the rest of the series, there was this reply from the previous round I can expand on.

On 02/05/2023 08:50, Tvrtko Ursulin wrote:

On 01/05/2023 17:58, Rob Clark wrote:
On Fri, Apr 28, 2023 at 4:05 AM Tvrtko Ursulin
<tvrtko.ursulin@xxxxxxxxxxxxxxx> wrote:


On 27/04/2023 18:53, Rob Clark wrote:
From: Rob Clark <robdclark@xxxxxxxxxxxx>

These are useful in particular for VM scenarios where the process which
has opened to drm device file is just a proxy for the real user in a VM
guest.

Signed-off-by: Rob Clark <robdclark@xxxxxxxxxxxx>
---
   Documentation/gpu/drm-usage-stats.rst | 18 ++++++++++++++++++
   drivers/gpu/drm/drm_file.c            | 15 +++++++++++++++
   include/drm/drm_file.h                | 19 +++++++++++++++++++
   3 files changed, 52 insertions(+)

diff --git a/Documentation/gpu/drm-usage-stats.rst b/Documentation/gpu/drm-usage-stats.rst
index 58dc0d3f8c58..e4877cf8089c 100644
--- a/Documentation/gpu/drm-usage-stats.rst
+++ b/Documentation/gpu/drm-usage-stats.rst
@@ -73,6 +73,24 @@ scope of each device, in which case `drm-pdev` shall be present as well.    Userspace should make sure to not double account any usage statistics by using    the above described criteria in order to associate data to individual clients.

+- drm-comm-override: <valstr>
+
+Returns the client executable override string.  Some drivers support letting +userspace override this in cases where the userspace is simply a "proxy". +Such as is the case with virglrenderer drm native context, where the host +process is just forwarding command submission, etc, from guest userspace. +This allows the proxy to make visible the executable name of the actual
+app in the VM guest.
+
+- drm-cmdline-override: <valstr>
+
+Returns the client cmdline override string.  Some drivers support letting +userspace override this in cases where the userspace is simply a "proxy". +Such as is the case with virglrenderer drm native context, where the host +process is just forwarding command submission, etc, from guest userspace. +This allows the proxy to make visible the cmdline of the actual app in the
+VM guest.

Perhaps it would be okay to save space here by not repeating the
description, like:

drm-comm-override: <valstr>
drm-cmdline-override: <valstr>

Long description blah blah...
This allows the proxy to make visible the _executable name *and* command
line_ blah blah..

+
   Utilization
   ^^^^^^^^^^^

diff --git a/drivers/gpu/drm/drm_file.c b/drivers/gpu/drm/drm_file.c
index 9321eb0bf020..d7514c313af1 100644
--- a/drivers/gpu/drm/drm_file.c
+++ b/drivers/gpu/drm/drm_file.c
@@ -178,6 +178,8 @@ struct drm_file *drm_file_alloc(struct drm_minor *minor)
       spin_lock_init(&file->master_lookup_lock);
       mutex_init(&file->event_read_lock);

+     mutex_init(&file->override_lock);
+
       if (drm_core_check_feature(dev, DRIVER_GEM))
               drm_gem_open(dev, file);

@@ -292,6 +294,8 @@ void drm_file_free(struct drm_file *file)
       WARN_ON(!list_empty(&file->event_list));

       put_pid(file->pid);
+     kfree(file->override_comm);
+     kfree(file->override_cmdline);
       kfree(file);
   }

@@ -995,6 +999,17 @@ void drm_show_fdinfo(struct seq_file *m, struct file *f)                           PCI_SLOT(pdev->devfn), PCI_FUNC(pdev->devfn));
       }

+     mutex_lock(&file->override_lock);

You could add a fast unlocked check before taking the mutex for no risk
apart a transient false negative. For 99.9999% of userspace it would
mean no pointless lock/unlock cycle.

I'm not sure I get your point?  This needs to be serialized against
userspace setting the override values

if (file->override_comm || file->override_cmdline) {
     mutex_lock(&file->override_lock);
     if (file->override_comm)
         drm_printf(&p, "drm-comm-override:\t%s\n",
                file->override_comm);
     if (file->override_cmdline)
         drm_printf(&p, "drm-cmdline-override:\t%s\n",
                file->override_cmdline);
     mutext_unlock(&file->override_lock);
}

No risk apart for a transient false negative (which is immaterial for userspace since fdinfo reads are not ordered versus the override setting anyway) and 99.9% of deployments can get by not needing to pointlessly cycle the lock.

This fast path bypass I think is worth it but up to you if you are really opposed. It's just that I don't see a point for cycling the mutex for nothing in majority of cases.


+     if (file->override_comm) {
+             drm_printf(&p, "drm-comm-override:\t%s\n",
+                        file->override_comm);
+     }
+     if (file->override_cmdline) {
+             drm_printf(&p, "drm-cmdline-override:\t%s\n",
+                        file->override_cmdline);
+     }
+     mutex_unlock(&file->override_lock);
+
       if (dev->driver->show_fdinfo)
               dev->driver->show_fdinfo(&p, file);
   }
diff --git a/include/drm/drm_file.h b/include/drm/drm_file.h
index 1339e925af52..604d05fa6f0c 100644
--- a/include/drm/drm_file.h
+++ b/include/drm/drm_file.h
@@ -370,6 +370,25 @@ struct drm_file {
        */
       struct drm_prime_file_private prime;

+     /**
+      * @comm: Overridden task comm
+      *
+      * Accessed under override_lock
+      */
+     char *override_comm;
+
+     /**
+      * @cmdline: Overridden task cmdline
+      *
+      * Accessed under override_lock
+      */
+     char *override_cmdline;
+
+     /**
+      * @override_lock: Serialize access to override_comm and override_cmdline
+      */
+     struct mutex override_lock;
+

I don't think this should go to drm just yet though. Only one driver can
make use of it so I'd leave it for later and print from msm_show_fdinfo
for now.

This was my original approach but danvet asked that it be moved into
drm for consistency across drivers.  (And really, I want the in-flight
amd and intel native-context stuff to motivate adding similar features
to amdgpu/i915/xe.)

IMO if implementation is not shared, not even by using helpers, I don't think data storage should be either, but it's not a deal breaker.

To summarise my thoughts on the patch (v4):

I am not really keen on the split of data fields in common and no common implementation or helpers.

For what the drm-usage-stats.rst are concerned it looks completely fine. And feature really will be useful in virtualised stacks.

Code in this patch is also completely fine.

Therefore you can have an r-b on those parts, but with reservations on whether it makes sense to put the fields under drm_file just yet. That should be fine under the r-b rules AFAIU. Ideally you can collect an ack from someone else too.

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>

Regards,

Tvrtko


Regards,

Tvrtko


BR,
-R

Regards,

Tvrtko

       /* private: */
   #if IS_ENABLED(CONFIG_DRM_LEGACY)
       unsigned long lock_count; /* DRI1 legacy lock count */



[Index of Archives]     [Linux DRI Users]     [Linux Intel Graphics]     [Linux USB Devel]     [Video for Linux]     [Linux Audio Users]     [Yosemite News]     [Linux Kernel]     [Linux SCSI]     [XFree86]     [Linux USB Devel]     [Video for Linux]     [Linux Audio Users]     [Linux Kernel]     [Linux SCSI]     [XFree86]
  Powered by Linux