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

[Rob Clark]

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) {
> > +             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.)

BR,
-R

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