Re: [PATCH v2 8/9] drm/fdinfo: Add comm/cmdline override fields
From: Tvrtko Ursulin
Date: Thu May 18 2023 - 05:43:28 EST
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 */