On Thu, 18 Dec 2025 14:54:35 -0800 Chia-I Wu <[email protected]> wrote:
> On Thu, Dec 18, 2025 at 10:36 AM Boris Brezillon > <[email protected]> wrote: > > > > On Thu, 18 Dec 2025 16:57:28 +0000 > > Steven Price <[email protected]> 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 <[email protected]> > > > > Signed-off-by: Ketil Johnsen <[email protected]> > > > > --- > > > > 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); > > > > >
