[v1] drm/panthor: Evict groups before VM termination

[PATCH] drm/panthor: Evict groups before VM termination

Posted by Ketil Johnsen 1 month, 3 weeks ago

Ensure all related groups are evicted and suspended before VM
destruction takes place.

This fixes an issue where panthor_vm_destroy() destroys and unmaps the
heap context while there are still on slot groups using this.
The FW will do a write out to the heap context when a CSG (group) is
suspended, so a premature unmap of the heap context will cause a
GPU page fault.
This page fault is quite harmless, and do not affect the continued
operation of the GPU.

Fixes: 647810ec2476 ("drm/panthor: Add the MMU/VM logical block")
Co-developed-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Ketil Johnsen <ketil.johnsen@arm.com>
---
 drivers/gpu/drm/panthor/panthor_mmu.c   |  4 ++++
 drivers/gpu/drm/panthor/panthor_sched.c | 16 ++++++++++++++++
 drivers/gpu/drm/panthor/panthor_sched.h |  1 +
 3 files changed, 21 insertions(+)

diff --git a/drivers/gpu/drm/panthor/panthor_mmu.c b/drivers/gpu/drm/panthor/panthor_mmu.c
index 74230f7199121..0e4b301a9c70e 100644
--- a/drivers/gpu/drm/panthor/panthor_mmu.c
+++ b/drivers/gpu/drm/panthor/panthor_mmu.c
@@ -1537,6 +1537,10 @@ static void panthor_vm_destroy(struct panthor_vm *vm)
 
 	vm->destroyed = true;
 
+	/* Tell scheduler to stop all GPU work related to this VM */
+	if (refcount_read(&vm->as.active_cnt) > 0)
+		panthor_sched_prepare_for_vm_destruction(vm->ptdev);
+
 	mutex_lock(&vm->heaps.lock);
 	panthor_heap_pool_destroy(vm->heaps.pool);
 	vm->heaps.pool = NULL;
diff --git a/drivers/gpu/drm/panthor/panthor_sched.c b/drivers/gpu/drm/panthor/panthor_sched.c
index f680edcd40aad..fbbaab9b25efb 100644
--- a/drivers/gpu/drm/panthor/panthor_sched.c
+++ b/drivers/gpu/drm/panthor/panthor_sched.c
@@ -2930,6 +2930,22 @@ void panthor_sched_report_mmu_fault(struct panthor_device *ptdev)
 		sched_queue_delayed_work(ptdev->scheduler, tick, 0);
 }
 
+void panthor_sched_prepare_for_vm_destruction(struct panthor_device *ptdev)
+{
+	/* FW can write out internal state, like the heap context, during CSG
+	 * suspend. It is therefore important that the scheduler has fully
+	 * evicted any pending and related groups before VM destruction can
+	 * safely continue. Failure to do so can lead to GPU page faults.
+	 * A controlled termination of a Panthor instance involves destroying
+	 * the group(s) before the VM. This means any relevant group eviction
+	 * has already been initiated by this point, and we just need to
+	 * ensure that any pending tick_work() has been completed.
+	 */
+	if (ptdev->scheduler) {
+		flush_work(&ptdev->scheduler->tick_work.work);
+	}
+}
+
 void panthor_sched_resume(struct panthor_device *ptdev)
 {
 	/* Force a tick to re-evaluate after a resume. */
diff --git a/drivers/gpu/drm/panthor/panthor_sched.h b/drivers/gpu/drm/panthor/panthor_sched.h
index f4a475aa34c0a..9a8692de8aded 100644
--- a/drivers/gpu/drm/panthor/panthor_sched.h
+++ b/drivers/gpu/drm/panthor/panthor_sched.h
@@ -50,6 +50,7 @@ void panthor_sched_suspend(struct panthor_device *ptdev);
 void panthor_sched_resume(struct panthor_device *ptdev);
 
 void panthor_sched_report_mmu_fault(struct panthor_device *ptdev);
+void panthor_sched_prepare_for_vm_destruction(struct panthor_device *ptdev);
 void panthor_sched_report_fw_events(struct panthor_device *ptdev, u32 events);
 
 void panthor_fdinfo_gather_group_samples(struct panthor_file *pfile);
-- 
2.43.0

Re: [PATCH] drm/panthor: Evict groups before VM termination

Posted by Boris Brezillon 1 month, 2 weeks ago

On Thu, 18 Dec 2025 17:26:42 +0100
Ketil Johnsen <ketil.johnsen@arm.com> wrote:

> Ensure all related groups are evicted and suspended before VM
> destruction takes place.
> 
> This fixes an issue where panthor_vm_destroy() destroys and unmaps the
> heap context while there are still on slot groups using this.
> The FW will do a write out to the heap context when a CSG (group) is
> suspended, so a premature unmap of the heap context will cause a
> GPU page fault.
> This page fault is quite harmless, and do not affect the continued
> operation of the GPU.
> 
> Fixes: 647810ec2476 ("drm/panthor: Add the MMU/VM logical block")
> Co-developed-by: Boris Brezillon <boris.brezillon@collabora.com>
> Signed-off-by: Ketil Johnsen <ketil.johnsen@arm.com>

Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>

> ---
>  drivers/gpu/drm/panthor/panthor_mmu.c   |  4 ++++
>  drivers/gpu/drm/panthor/panthor_sched.c | 16 ++++++++++++++++
>  drivers/gpu/drm/panthor/panthor_sched.h |  1 +
>  3 files changed, 21 insertions(+)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_mmu.c b/drivers/gpu/drm/panthor/panthor_mmu.c
> index 74230f7199121..0e4b301a9c70e 100644
> --- a/drivers/gpu/drm/panthor/panthor_mmu.c
> +++ b/drivers/gpu/drm/panthor/panthor_mmu.c
> @@ -1537,6 +1537,10 @@ static void panthor_vm_destroy(struct panthor_vm *vm)
>  
>  	vm->destroyed = true;
>  
> +	/* Tell scheduler to stop all GPU work related to this VM */
> +	if (refcount_read(&vm->as.active_cnt) > 0)
> +		panthor_sched_prepare_for_vm_destruction(vm->ptdev);
> +
>  	mutex_lock(&vm->heaps.lock);
>  	panthor_heap_pool_destroy(vm->heaps.pool);
>  	vm->heaps.pool = NULL;
> diff --git a/drivers/gpu/drm/panthor/panthor_sched.c b/drivers/gpu/drm/panthor/panthor_sched.c
> index f680edcd40aad..fbbaab9b25efb 100644
> --- a/drivers/gpu/drm/panthor/panthor_sched.c
> +++ b/drivers/gpu/drm/panthor/panthor_sched.c
> @@ -2930,6 +2930,22 @@ void panthor_sched_report_mmu_fault(struct panthor_device *ptdev)
>  		sched_queue_delayed_work(ptdev->scheduler, tick, 0);
>  }
>  
> +void panthor_sched_prepare_for_vm_destruction(struct panthor_device *ptdev)
> +{
> +	/* FW can write out internal state, like the heap context, during CSG
> +	 * suspend. It is therefore important that the scheduler has fully
> +	 * evicted any pending and related groups before VM destruction can
> +	 * safely continue. Failure to do so can lead to GPU page faults.
> +	 * A controlled termination of a Panthor instance involves destroying
> +	 * the group(s) before the VM. This means any relevant group eviction
> +	 * has already been initiated by this point, and we just need to
> +	 * ensure that any pending tick_work() has been completed.
> +	 */
> +	if (ptdev->scheduler) {
> +		flush_work(&ptdev->scheduler->tick_work.work);
> +	}

nit: you can drop the curly braces on single line conditionals. No
need to send a v2, I can fix this up when applying.

> +}
> +
>  void panthor_sched_resume(struct panthor_device *ptdev)
>  {
>  	/* Force a tick to re-evaluate after a resume. */
> diff --git a/drivers/gpu/drm/panthor/panthor_sched.h b/drivers/gpu/drm/panthor/panthor_sched.h
> index f4a475aa34c0a..9a8692de8aded 100644
> --- a/drivers/gpu/drm/panthor/panthor_sched.h
> +++ b/drivers/gpu/drm/panthor/panthor_sched.h
> @@ -50,6 +50,7 @@ void panthor_sched_suspend(struct panthor_device *ptdev);
>  void panthor_sched_resume(struct panthor_device *ptdev);
>  
>  void panthor_sched_report_mmu_fault(struct panthor_device *ptdev);
> +void panthor_sched_prepare_for_vm_destruction(struct panthor_device *ptdev);
>  void panthor_sched_report_fw_events(struct panthor_device *ptdev, u32 events);
>  
>  void panthor_fdinfo_gather_group_samples(struct panthor_file *pfile);

Re: [PATCH] drm/panthor: Evict groups before VM termination

Posted by Steven Price 1 month, 3 weeks ago

On 18/12/2025 16:26, Ketil Johnsen wrote:
> Ensure all related groups are evicted and suspended before VM
> destruction takes place.
> 
> This fixes an issue where panthor_vm_destroy() destroys and unmaps the
> heap context while there are still on slot groups using this.
> The FW will do a write out to the heap context when a CSG (group) is
> suspended, so a premature unmap of the heap context will cause a
> GPU page fault.
> This page fault is quite harmless, and do not affect the continued
> operation of the GPU.
> 
> Fixes: 647810ec2476 ("drm/panthor: Add the MMU/VM logical block")
> Co-developed-by: Boris Brezillon <boris.brezillon@collabora.com>
> Signed-off-by: Ketil Johnsen <ketil.johnsen@arm.com>
> ---
>  drivers/gpu/drm/panthor/panthor_mmu.c   |  4 ++++
>  drivers/gpu/drm/panthor/panthor_sched.c | 16 ++++++++++++++++
>  drivers/gpu/drm/panthor/panthor_sched.h |  1 +
>  3 files changed, 21 insertions(+)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_mmu.c b/drivers/gpu/drm/panthor/panthor_mmu.c
> index 74230f7199121..0e4b301a9c70e 100644
> --- a/drivers/gpu/drm/panthor/panthor_mmu.c
> +++ b/drivers/gpu/drm/panthor/panthor_mmu.c
> @@ -1537,6 +1537,10 @@ static void panthor_vm_destroy(struct panthor_vm *vm)
>  
>  	vm->destroyed = true;
>  
> +	/* Tell scheduler to stop all GPU work related to this VM */
> +	if (refcount_read(&vm->as.active_cnt) > 0)
> +		panthor_sched_prepare_for_vm_destruction(vm->ptdev);
> +
>  	mutex_lock(&vm->heaps.lock);
>  	panthor_heap_pool_destroy(vm->heaps.pool);
>  	vm->heaps.pool = NULL;
> diff --git a/drivers/gpu/drm/panthor/panthor_sched.c b/drivers/gpu/drm/panthor/panthor_sched.c
> index f680edcd40aad..fbbaab9b25efb 100644
> --- a/drivers/gpu/drm/panthor/panthor_sched.c
> +++ b/drivers/gpu/drm/panthor/panthor_sched.c
> @@ -2930,6 +2930,22 @@ void panthor_sched_report_mmu_fault(struct panthor_device *ptdev)
>  		sched_queue_delayed_work(ptdev->scheduler, tick, 0);
>  }
>  
> +void panthor_sched_prepare_for_vm_destruction(struct panthor_device *ptdev)
> +{
> +	/* FW can write out internal state, like the heap context, during CSG
> +	 * suspend. It is therefore important that the scheduler has fully
> +	 * evicted any pending and related groups before VM destruction can
> +	 * safely continue. Failure to do so can lead to GPU page faults.
> +	 * A controlled termination of a Panthor instance involves destroying
> +	 * the group(s) before the VM. This means any relevant group eviction
> +	 * has already been initiated by this point, and we just need to
> +	 * ensure that any pending tick_work() has been completed.
> +	 */
> +	if (ptdev->scheduler) {
> +		flush_work(&ptdev->scheduler->tick_work.work);
> +	}

NIT: braces not needed.

But I'm also struggling to understand in what situation ptdev->scheduler
would be NULL?

Thanks,
Steve

> +}
> +
>  void panthor_sched_resume(struct panthor_device *ptdev)
>  {
>  	/* Force a tick to re-evaluate after a resume. */
> diff --git a/drivers/gpu/drm/panthor/panthor_sched.h b/drivers/gpu/drm/panthor/panthor_sched.h
> index f4a475aa34c0a..9a8692de8aded 100644
> --- a/drivers/gpu/drm/panthor/panthor_sched.h
> +++ b/drivers/gpu/drm/panthor/panthor_sched.h
> @@ -50,6 +50,7 @@ void panthor_sched_suspend(struct panthor_device *ptdev);
>  void panthor_sched_resume(struct panthor_device *ptdev);
>  
>  void panthor_sched_report_mmu_fault(struct panthor_device *ptdev);
> +void panthor_sched_prepare_for_vm_destruction(struct panthor_device *ptdev);
>  void panthor_sched_report_fw_events(struct panthor_device *ptdev, u32 events);
>  
>  void panthor_fdinfo_gather_group_samples(struct panthor_file *pfile);

Re: [PATCH] drm/panthor: Evict groups before VM termination

Posted by Boris Brezillon 1 month, 2 weeks ago

On Thu, 18 Dec 2025 16:57:28 +0000
Steven Price <steven.price@arm.com> wrote:

> On 18/12/2025 16:26, Ketil Johnsen wrote:
> > Ensure all related groups are evicted and suspended before VM
> > destruction takes place.
> > 
> > This fixes an issue where panthor_vm_destroy() destroys and unmaps the
> > heap context while there are still on slot groups using this.
> > The FW will do a write out to the heap context when a CSG (group) is
> > suspended, so a premature unmap of the heap context will cause a
> > GPU page fault.
> > This page fault is quite harmless, and do not affect the continued
> > operation of the GPU.
> > 
> > Fixes: 647810ec2476 ("drm/panthor: Add the MMU/VM logical block")
> > Co-developed-by: Boris Brezillon <boris.brezillon@collabora.com>
> > Signed-off-by: Ketil Johnsen <ketil.johnsen@arm.com>
> > ---
> >  drivers/gpu/drm/panthor/panthor_mmu.c   |  4 ++++
> >  drivers/gpu/drm/panthor/panthor_sched.c | 16 ++++++++++++++++
> >  drivers/gpu/drm/panthor/panthor_sched.h |  1 +
> >  3 files changed, 21 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/panthor/panthor_mmu.c b/drivers/gpu/drm/panthor/panthor_mmu.c
> > index 74230f7199121..0e4b301a9c70e 100644
> > --- a/drivers/gpu/drm/panthor/panthor_mmu.c
> > +++ b/drivers/gpu/drm/panthor/panthor_mmu.c
> > @@ -1537,6 +1537,10 @@ static void panthor_vm_destroy(struct panthor_vm *vm)
> >  
> >  	vm->destroyed = true;
> >  
> > +	/* Tell scheduler to stop all GPU work related to this VM */
> > +	if (refcount_read(&vm->as.active_cnt) > 0)
> > +		panthor_sched_prepare_for_vm_destruction(vm->ptdev);
> > +
> >  	mutex_lock(&vm->heaps.lock);
> >  	panthor_heap_pool_destroy(vm->heaps.pool);
> >  	vm->heaps.pool = NULL;
> > diff --git a/drivers/gpu/drm/panthor/panthor_sched.c b/drivers/gpu/drm/panthor/panthor_sched.c
> > index f680edcd40aad..fbbaab9b25efb 100644
> > --- a/drivers/gpu/drm/panthor/panthor_sched.c
> > +++ b/drivers/gpu/drm/panthor/panthor_sched.c
> > @@ -2930,6 +2930,22 @@ void panthor_sched_report_mmu_fault(struct panthor_device *ptdev)
> >  		sched_queue_delayed_work(ptdev->scheduler, tick, 0);
> >  }
> >  
> > +void panthor_sched_prepare_for_vm_destruction(struct panthor_device *ptdev)
> > +{
> > +	/* FW can write out internal state, like the heap context, during CSG
> > +	 * suspend. It is therefore important that the scheduler has fully
> > +	 * evicted any pending and related groups before VM destruction can
> > +	 * safely continue. Failure to do so can lead to GPU page faults.
> > +	 * A controlled termination of a Panthor instance involves destroying
> > +	 * the group(s) before the VM. This means any relevant group eviction
> > +	 * has already been initiated by this point, and we just need to
> > +	 * ensure that any pending tick_work() has been completed.
> > +	 */
> > +	if (ptdev->scheduler) {
> > +		flush_work(&ptdev->scheduler->tick_work.work);
> > +	}  
> 
> NIT: braces not needed.
> 
> But I'm also struggling to understand in what situation ptdev->scheduler
> would be NULL?

I thought it could happen if the FW initialization fails in the middle,
and the FW VM is destroyed before the scheduler had a chance to
initialize, but it turns out the FW logic never calls
panthor_vm_destroy().

> 
> Thanks,
> Steve
> 
> > +}
> > +
> >  void panthor_sched_resume(struct panthor_device *ptdev)
> >  {
> >  	/* Force a tick to re-evaluate after a resume. */
> > diff --git a/drivers/gpu/drm/panthor/panthor_sched.h b/drivers/gpu/drm/panthor/panthor_sched.h
> > index f4a475aa34c0a..9a8692de8aded 100644
> > --- a/drivers/gpu/drm/panthor/panthor_sched.h
> > +++ b/drivers/gpu/drm/panthor/panthor_sched.h
> > @@ -50,6 +50,7 @@ void panthor_sched_suspend(struct panthor_device *ptdev);
> >  void panthor_sched_resume(struct panthor_device *ptdev);
> >  
> >  void panthor_sched_report_mmu_fault(struct panthor_device *ptdev);
> > +void panthor_sched_prepare_for_vm_destruction(struct panthor_device *ptdev);
> >  void panthor_sched_report_fw_events(struct panthor_device *ptdev, u32 events);
> >  
> >  void panthor_fdinfo_gather_group_samples(struct panthor_file *pfile);  
>

Re: [PATCH] drm/panthor: Evict groups before VM termination

Posted by Ketil Johnsen 1 month, 2 weeks ago

On 12/18/25 18:59, Boris Brezillon wrote:
> On Thu, 18 Dec 2025 16:57:28 +0000
> Steven Price <steven.price@arm.com> wrote:
> 
>> On 18/12/2025 16:26, Ketil Johnsen wrote:
>>> Ensure all related groups are evicted and suspended before VM
>>> destruction takes place.
>>>
>>> This fixes an issue where panthor_vm_destroy() destroys and unmaps the
>>> heap context while there are still on slot groups using this.
>>> The FW will do a write out to the heap context when a CSG (group) is
>>> suspended, so a premature unmap of the heap context will cause a
>>> GPU page fault.
>>> This page fault is quite harmless, and do not affect the continued
>>> operation of the GPU.
>>>
>>> Fixes: 647810ec2476 ("drm/panthor: Add the MMU/VM logical block")
>>> Co-developed-by: Boris Brezillon <boris.brezillon@collabora.com>
>>> Signed-off-by: Ketil Johnsen <ketil.johnsen@arm.com>
>>> ---
>>>   drivers/gpu/drm/panthor/panthor_mmu.c   |  4 ++++
>>>   drivers/gpu/drm/panthor/panthor_sched.c | 16 ++++++++++++++++
>>>   drivers/gpu/drm/panthor/panthor_sched.h |  1 +
>>>   3 files changed, 21 insertions(+)
>>>
>>> diff --git a/drivers/gpu/drm/panthor/panthor_mmu.c b/drivers/gpu/drm/panthor/panthor_mmu.c
>>> index 74230f7199121..0e4b301a9c70e 100644
>>> --- a/drivers/gpu/drm/panthor/panthor_mmu.c
>>> +++ b/drivers/gpu/drm/panthor/panthor_mmu.c
>>> @@ -1537,6 +1537,10 @@ static void panthor_vm_destroy(struct panthor_vm *vm)
>>>   
>>>   	vm->destroyed = true;
>>>   
>>> +	/* Tell scheduler to stop all GPU work related to this VM */
>>> +	if (refcount_read(&vm->as.active_cnt) > 0)
>>> +		panthor_sched_prepare_for_vm_destruction(vm->ptdev);
>>> +
>>>   	mutex_lock(&vm->heaps.lock);
>>>   	panthor_heap_pool_destroy(vm->heaps.pool);
>>>   	vm->heaps.pool = NULL;
>>> diff --git a/drivers/gpu/drm/panthor/panthor_sched.c b/drivers/gpu/drm/panthor/panthor_sched.c
>>> index f680edcd40aad..fbbaab9b25efb 100644
>>> --- a/drivers/gpu/drm/panthor/panthor_sched.c
>>> +++ b/drivers/gpu/drm/panthor/panthor_sched.c
>>> @@ -2930,6 +2930,22 @@ void panthor_sched_report_mmu_fault(struct panthor_device *ptdev)
>>>   		sched_queue_delayed_work(ptdev->scheduler, tick, 0);
>>>   }
>>>   
>>> +void panthor_sched_prepare_for_vm_destruction(struct panthor_device *ptdev)
>>> +{
>>> +	/* FW can write out internal state, like the heap context, during CSG
>>> +	 * suspend. It is therefore important that the scheduler has fully
>>> +	 * evicted any pending and related groups before VM destruction can
>>> +	 * safely continue. Failure to do so can lead to GPU page faults.
>>> +	 * A controlled termination of a Panthor instance involves destroying
>>> +	 * the group(s) before the VM. This means any relevant group eviction
>>> +	 * has already been initiated by this point, and we just need to
>>> +	 * ensure that any pending tick_work() has been completed.
>>> +	 */
>>> +	if (ptdev->scheduler) {
>>> +		flush_work(&ptdev->scheduler->tick_work.work);
>>> +	}
>>
>> NIT: braces not needed.
>>
>> But I'm also struggling to understand in what situation ptdev->scheduler
>> would be NULL?
> 
> I thought it could happen if the FW initialization fails in the middle,
> and the FW VM is destroyed before the scheduler had a chance to
> initialize, but it turns out the FW logic never calls
> panthor_vm_destroy().

Yes, I also think we can safely drop the check. I even injected some 
probe errors to double check, and I see that we still terminate the FW 
VM successfully (as this is not executed in this case).

I will send a v2 shortly with this check (and braces) removed.

--
Thanks,
Ketil


>> Thanks,
>> Steve
>>
>>> +}
>>> +
>>>   void panthor_sched_resume(struct panthor_device *ptdev)
>>>   {
>>>   	/* Force a tick to re-evaluate after a resume. */
>>> diff --git a/drivers/gpu/drm/panthor/panthor_sched.h b/drivers/gpu/drm/panthor/panthor_sched.h
>>> index f4a475aa34c0a..9a8692de8aded 100644
>>> --- a/drivers/gpu/drm/panthor/panthor_sched.h
>>> +++ b/drivers/gpu/drm/panthor/panthor_sched.h
>>> @@ -50,6 +50,7 @@ void panthor_sched_suspend(struct panthor_device *ptdev);
>>>   void panthor_sched_resume(struct panthor_device *ptdev);
>>>   
>>>   void panthor_sched_report_mmu_fault(struct panthor_device *ptdev);
>>> +void panthor_sched_prepare_for_vm_destruction(struct panthor_device *ptdev);
>>>   void panthor_sched_report_fw_events(struct panthor_device *ptdev, u32 events);
>>>   
>>>   void panthor_fdinfo_gather_group_samples(struct panthor_file *pfile);
>>
>

Re: [PATCH] drm/panthor: Evict groups before VM termination

Posted by Chia-I Wu 1 month, 2 weeks ago

On Thu, Dec 18, 2025 at 10:36 AM Boris Brezillon
<boris.brezillon@collabora.com> wrote:
>
> On Thu, 18 Dec 2025 16:57:28 +0000
> Steven Price <steven.price@arm.com> wrote:
>
> > On 18/12/2025 16:26, Ketil Johnsen wrote:
> > > Ensure all related groups are evicted and suspended before VM
> > > destruction takes place.
> > >
> > > This fixes an issue where panthor_vm_destroy() destroys and unmaps the
> > > heap context while there are still on slot groups using this.
> > > The FW will do a write out to the heap context when a CSG (group) is
> > > suspended, so a premature unmap of the heap context will cause a
> > > GPU page fault.
> > > This page fault is quite harmless, and do not affect the continued
> > > operation of the GPU.
> > >
> > > Fixes: 647810ec2476 ("drm/panthor: Add the MMU/VM logical block")
> > > Co-developed-by: Boris Brezillon <boris.brezillon@collabora.com>
> > > Signed-off-by: Ketil Johnsen <ketil.johnsen@arm.com>
> > > ---
> > >  drivers/gpu/drm/panthor/panthor_mmu.c   |  4 ++++
> > >  drivers/gpu/drm/panthor/panthor_sched.c | 16 ++++++++++++++++
> > >  drivers/gpu/drm/panthor/panthor_sched.h |  1 +
> > >  3 files changed, 21 insertions(+)
> > >
> > > diff --git a/drivers/gpu/drm/panthor/panthor_mmu.c b/drivers/gpu/drm/panthor/panthor_mmu.c
> > > index 74230f7199121..0e4b301a9c70e 100644
> > > --- a/drivers/gpu/drm/panthor/panthor_mmu.c
> > > +++ b/drivers/gpu/drm/panthor/panthor_mmu.c
> > > @@ -1537,6 +1537,10 @@ static void panthor_vm_destroy(struct panthor_vm *vm)
> > >
> > >     vm->destroyed = true;
> > >
> > > +   /* Tell scheduler to stop all GPU work related to this VM */
> > > +   if (refcount_read(&vm->as.active_cnt) > 0)
> > > +           panthor_sched_prepare_for_vm_destruction(vm->ptdev);
> > > +
> > >     mutex_lock(&vm->heaps.lock);
> > >     panthor_heap_pool_destroy(vm->heaps.pool);
> > >     vm->heaps.pool = NULL;
Is it better to remove the panthor_heap_pool_destroy call here instead
and let panthor_vm_free take care of it?

> > > diff --git a/drivers/gpu/drm/panthor/panthor_sched.c b/drivers/gpu/drm/panthor/panthor_sched.c
> > > index f680edcd40aad..fbbaab9b25efb 100644
> > > --- a/drivers/gpu/drm/panthor/panthor_sched.c
> > > +++ b/drivers/gpu/drm/panthor/panthor_sched.c
> > > @@ -2930,6 +2930,22 @@ void panthor_sched_report_mmu_fault(struct panthor_device *ptdev)
> > >             sched_queue_delayed_work(ptdev->scheduler, tick, 0);
> > >  }
> > >
> > > +void panthor_sched_prepare_for_vm_destruction(struct panthor_device *ptdev)
> > > +{
> > > +   /* FW can write out internal state, like the heap context, during CSG
> > > +    * suspend. It is therefore important that the scheduler has fully
> > > +    * evicted any pending and related groups before VM destruction can
> > > +    * safely continue. Failure to do so can lead to GPU page faults.
> > > +    * A controlled termination of a Panthor instance involves destroying
> > > +    * the group(s) before the VM. This means any relevant group eviction
> > > +    * has already been initiated by this point, and we just need to
> > > +    * ensure that any pending tick_work() has been completed.
> > > +    */
> > > +   if (ptdev->scheduler) {
> > > +           flush_work(&ptdev->scheduler->tick_work.work);
> > > +   }
> >
> > NIT: braces not needed.
> >
> > But I'm also struggling to understand in what situation ptdev->scheduler
> > would be NULL?
>
> I thought it could happen if the FW initialization fails in the middle,
> and the FW VM is destroyed before the scheduler had a chance to
> initialize, but it turns out the FW logic never calls
> panthor_vm_destroy().
>
> >
> > Thanks,
> > Steve
> >
> > > +}
> > > +
> > >  void panthor_sched_resume(struct panthor_device *ptdev)
> > >  {
> > >     /* Force a tick to re-evaluate after a resume. */
> > > diff --git a/drivers/gpu/drm/panthor/panthor_sched.h b/drivers/gpu/drm/panthor/panthor_sched.h
> > > index f4a475aa34c0a..9a8692de8aded 100644
> > > --- a/drivers/gpu/drm/panthor/panthor_sched.h
> > > +++ b/drivers/gpu/drm/panthor/panthor_sched.h
> > > @@ -50,6 +50,7 @@ void panthor_sched_suspend(struct panthor_device *ptdev);
> > >  void panthor_sched_resume(struct panthor_device *ptdev);
> > >
> > >  void panthor_sched_report_mmu_fault(struct panthor_device *ptdev);
> > > +void panthor_sched_prepare_for_vm_destruction(struct panthor_device *ptdev);
> > >  void panthor_sched_report_fw_events(struct panthor_device *ptdev, u32 events);
> > >
> > >  void panthor_fdinfo_gather_group_samples(struct panthor_file *pfile);
> >
>

Re: [PATCH] drm/panthor: Evict groups before VM termination

Posted by Boris Brezillon 1 month, 2 weeks ago

On Thu, 18 Dec 2025 14:54:35 -0800
Chia-I Wu <olvaffe@gmail.com> wrote:

> On Thu, Dec 18, 2025 at 10:36 AM Boris Brezillon
> <boris.brezillon@collabora.com> wrote:
> >
> > On Thu, 18 Dec 2025 16:57:28 +0000
> > Steven Price <steven.price@arm.com> wrote:
> >  
> > > On 18/12/2025 16:26, Ketil Johnsen wrote:  
> > > > Ensure all related groups are evicted and suspended before VM
> > > > destruction takes place.
> > > >
> > > > This fixes an issue where panthor_vm_destroy() destroys and unmaps the
> > > > heap context while there are still on slot groups using this.
> > > > The FW will do a write out to the heap context when a CSG (group) is
> > > > suspended, so a premature unmap of the heap context will cause a
> > > > GPU page fault.
> > > > This page fault is quite harmless, and do not affect the continued
> > > > operation of the GPU.
> > > >
> > > > Fixes: 647810ec2476 ("drm/panthor: Add the MMU/VM logical block")
> > > > Co-developed-by: Boris Brezillon <boris.brezillon@collabora.com>
> > > > Signed-off-by: Ketil Johnsen <ketil.johnsen@arm.com>
> > > > ---
> > > >  drivers/gpu/drm/panthor/panthor_mmu.c   |  4 ++++
> > > >  drivers/gpu/drm/panthor/panthor_sched.c | 16 ++++++++++++++++
> > > >  drivers/gpu/drm/panthor/panthor_sched.h |  1 +
> > > >  3 files changed, 21 insertions(+)
> > > >
> > > > diff --git a/drivers/gpu/drm/panthor/panthor_mmu.c b/drivers/gpu/drm/panthor/panthor_mmu.c
> > > > index 74230f7199121..0e4b301a9c70e 100644
> > > > --- a/drivers/gpu/drm/panthor/panthor_mmu.c
> > > > +++ b/drivers/gpu/drm/panthor/panthor_mmu.c
> > > > @@ -1537,6 +1537,10 @@ static void panthor_vm_destroy(struct panthor_vm *vm)
> > > >
> > > >     vm->destroyed = true;
> > > >
> > > > +   /* Tell scheduler to stop all GPU work related to this VM */
> > > > +   if (refcount_read(&vm->as.active_cnt) > 0)
> > > > +           panthor_sched_prepare_for_vm_destruction(vm->ptdev);
> > > > +
> > > >     mutex_lock(&vm->heaps.lock);
> > > >     panthor_heap_pool_destroy(vm->heaps.pool);
> > > >     vm->heaps.pool = NULL;  
> Is it better to remove the panthor_heap_pool_destroy call here instead
> and let panthor_vm_free take care of it?

We can't because the heap_pool contains heap chunks (kernel BOs) that
are mapped in the very same VM, thus creating a circular ref. The whole
point of calling panthor_heap_pool_destroy() here is to kill this
circular ref. We could introduce the concept of weak and hard VM refs,
but I'm not sure it's worth it.

> 
> > > > diff --git a/drivers/gpu/drm/panthor/panthor_sched.c b/drivers/gpu/drm/panthor/panthor_sched.c
> > > > index f680edcd40aad..fbbaab9b25efb 100644
> > > > --- a/drivers/gpu/drm/panthor/panthor_sched.c
> > > > +++ b/drivers/gpu/drm/panthor/panthor_sched.c
> > > > @@ -2930,6 +2930,22 @@ void panthor_sched_report_mmu_fault(struct panthor_device *ptdev)
> > > >             sched_queue_delayed_work(ptdev->scheduler, tick, 0);
> > > >  }
> > > >
> > > > +void panthor_sched_prepare_for_vm_destruction(struct panthor_device *ptdev)
> > > > +{
> > > > +   /* FW can write out internal state, like the heap context, during CSG
> > > > +    * suspend. It is therefore important that the scheduler has fully
> > > > +    * evicted any pending and related groups before VM destruction can
> > > > +    * safely continue. Failure to do so can lead to GPU page faults.
> > > > +    * A controlled termination of a Panthor instance involves destroying
> > > > +    * the group(s) before the VM. This means any relevant group eviction
> > > > +    * has already been initiated by this point, and we just need to
> > > > +    * ensure that any pending tick_work() has been completed.
> > > > +    */
> > > > +   if (ptdev->scheduler) {
> > > > +           flush_work(&ptdev->scheduler->tick_work.work);
> > > > +   }  
> > >
> > > NIT: braces not needed.
> > >
> > > But I'm also struggling to understand in what situation ptdev->scheduler
> > > would be NULL?  
> >
> > I thought it could happen if the FW initialization fails in the middle,
> > and the FW VM is destroyed before the scheduler had a chance to
> > initialize, but it turns out the FW logic never calls
> > panthor_vm_destroy().
> >  
> > >
> > > Thanks,
> > > Steve
> > >  
> > > > +}
> > > > +
> > > >  void panthor_sched_resume(struct panthor_device *ptdev)
> > > >  {
> > > >     /* Force a tick to re-evaluate after a resume. */
> > > > diff --git a/drivers/gpu/drm/panthor/panthor_sched.h b/drivers/gpu/drm/panthor/panthor_sched.h
> > > > index f4a475aa34c0a..9a8692de8aded 100644
> > > > --- a/drivers/gpu/drm/panthor/panthor_sched.h
> > > > +++ b/drivers/gpu/drm/panthor/panthor_sched.h
> > > > @@ -50,6 +50,7 @@ void panthor_sched_suspend(struct panthor_device *ptdev);
> > > >  void panthor_sched_resume(struct panthor_device *ptdev);
> > > >
> > > >  void panthor_sched_report_mmu_fault(struct panthor_device *ptdev);
> > > > +void panthor_sched_prepare_for_vm_destruction(struct panthor_device *ptdev);
> > > >  void panthor_sched_report_fw_events(struct panthor_device *ptdev, u32 events);
> > > >
> > > >  void panthor_fdinfo_gather_group_samples(struct panthor_file *pfile);  
> > >  
> >