Re: [PATCH v4 1/5] drm/i915: Add engine reset count in get-reset-stats ioctl

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 06/03/2019 23:08, Carlos Santa wrote:
> On Mon, 2019-02-25 at 13:34 +0000, Tvrtko Ursulin wrote:
>> On 21/02/2019 02:58, Carlos Santa wrote:
>>> From: Michel Thierry <michel.thierry@intel.com>
>>>
>>> Users/tests relying on the total reset count will start seeing a
>>> smaller
>>> number since most of the hangs can be handled by engine reset.
>>> Note that if reset engine x, context a running on engine y will be
>>> unaware
>>> and unaffected.
>>>
>>> To start the discussion, include just a total engine reset count.
>>> If it
>>> is deemed useful, it can be extended to report each engine
>>> separately.
>>>
>>> Our igt's gem_reset_stats test will need changes to ignore the pad
>>> field,
>>> since it can now return reset_engine_count.
>>>
>>> v2: s/engine_reset/reset_engine/, use union in uapi to not break
>>> compatibility.
>>> v3: Keep rejecting attempts to use pad as input (Antonio)
>>> v4: Rebased.
>>> v5: Rebased.
>>>
>>> Cc: Chris Wilson <chris@chris-wilson.co.uk>
>>> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
>>> Cc: Antonio Argenziano <antonio.argenziano@intel.com>
>>> Cc: Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
>>> Signed-off-by: Michel Thierry <michel.thierry@intel.com>
>>> Signed-off-by: Carlos Santa <carlos.santa@intel.com>
>>> ---
>>>    drivers/gpu/drm/i915/i915_gem_context.c | 12 ++++++++++--
>>>    include/uapi/drm/i915_drm.h             |  6 +++++-
>>>    2 files changed, 15 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/i915/i915_gem_context.c
>>> b/drivers/gpu/drm/i915/i915_gem_context.c
>>> index 459f8eae1c39..cbfe8f2eb3f2 100644
>>> --- a/drivers/gpu/drm/i915/i915_gem_context.c
>>> +++ b/drivers/gpu/drm/i915/i915_gem_context.c
>>> @@ -1889,6 +1889,8 @@ int i915_gem_context_reset_stats_ioctl(struct
>>> drm_device *dev,
>>>    	struct drm_i915_private *dev_priv = to_i915(dev);
>>>    	struct drm_i915_reset_stats *args = data;
>>>    	struct i915_gem_context *ctx;
>>> +	struct intel_engine_cs *engine;
>>> +	enum intel_engine_id id;
>>>    	int ret;
>>>    
>>>    	if (args->flags || args->pad)
>>> @@ -1907,10 +1909,16 @@ int
>>> i915_gem_context_reset_stats_ioctl(struct drm_device *dev,
>>>    	 * we should wrap the hangstats with a seqlock.
>>>    	 */
>>>    
>>> -	if (capable(CAP_SYS_ADMIN))
>>> +	if (capable(CAP_SYS_ADMIN)) {
>>>    		args->reset_count = i915_reset_count(&dev_priv-
>>>> gpu_error);
>>> -	else
>>> +		for_each_engine(engine, dev_priv, id)
>>> +			args->reset_engine_count +=
>>> +				i915_reset_engine_count(&dev_priv-
>>>> gpu_error,
>>> +							engine);
>>
>> If access to global GPU reset count is privileged, why is access to
>> global engine reset count not? It seems to be fundamentally same
>> level
>> of data leakage.
> 
> But access to global engine reset count (i915_reset_engine_count) is
> indeed priviledged. They both are inside if(CAP_SYS_ADMIN){...}, or
> maybe I am missing something?

Looks like I misread the diff, sorry. Been processing a lot of patches 
lately.

Regards,

Tvrtko

>>
>> If we wanted to provide some numbers to unprivileged users I think
>> we
>> would need to store some counters per file_priv/context and return
>> those
>> when !CAP_SYS_ADMIN.
> 
> The question would be why access to global GPU reset count is
> priviledged then? I can't think of a reason why it should be
> priviledged. I think the new counter (per engine) should fall in the
> same category as the global GPU reset one, right? So, can we make them
> both unpriviledged?
> 
> 
>>
>>> +	} else {
>>>    		args->reset_count = 0;
>>> +		args->reset_engine_count = 0;
>>> +	}
>>>    
>>>    	args->batch_active = atomic_read(&ctx->guilty_count);
>>>    	args->batch_pending = atomic_read(&ctx->active_count);
>>> diff --git a/include/uapi/drm/i915_drm.h
>>> b/include/uapi/drm/i915_drm.h
>>> index cc03ef9f885f..3f2c89740b0e 100644
>>> --- a/include/uapi/drm/i915_drm.h
>>> +++ b/include/uapi/drm/i915_drm.h
>>> @@ -1642,7 +1642,11 @@ struct drm_i915_reset_stats {
>>>    	/* Number of batches lost pending for execution, for this
>>> context */
>>>    	__u32 batch_pending;
>>>    
>>> -	__u32 pad;
>>> +	union {
>>> +		__u32 pad;
>>> +		/* Engine resets since boot/module reload, for all
>>> contexts */
>>> +		__u32 reset_engine_count;
>>> +	};
>>
>> Chris pointed out in some other review that anonymous unions are not
>> friendly towards C++ compilers.
>>
>> Not sure what is the best option here. Renaming the field could
>> break
>> old userspace building against newer headers. Is that acceptable?
>>
> 
> I dug up some old comments from Chris and he stated that recycling the
> union like that would be a bad idea since that would make the pad field
> an output only parameter thus invalidating gem_reset_stats...
> 
> Why can't we simply add a new field __u32 reset_engine_count; as part
> of the drm_i915_reset_stats struct?
> 
> Regards,
> Carlos
> 
>>>    };
>>>    
>>>    struct drm_i915_gem_userptr {
>>>
>>
>> Regards,
>>
>> Tvrtko
> 
> 
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