Re: [Intel-xe] [RFC PATCH] drm/xe/dgfx: Release mmap mappings on rpm suspend

[Rodrigo Vivi <rodrigo.vivi@intel.com>]

On Mon, Aug 28, 2023 at 10:00:31PM +0530, Nilawar, Badal wrote:
> 
> 
> On 28-08-2023 17:46, Gupta, Anshuman wrote:
> > 
> > 
> > > -----Original Message-----
> > > From: Nilawar, Badal <badal.nilawar@intel.com>
> > > Sent: Thursday, August 24, 2023 11:16 PM
> > > To: intel-xe@lists.freedesktop.org
> > > Cc: Gupta, Anshuman <anshuman.gupta@intel.com>; Auld, Matthew
> > > <matthew.auld@intel.com>; Vivi, Rodrigo <rodrigo.vivi@intel.com>
> > > Subject: [RFC PATCH] drm/xe/dgfx: Release mmap mappings on rpm
> > > suspend
> > > 
> > > Release all mmap mappings for all vram objects which are associated with
> > > userfault such that, while pcie function in D3hot, any access to memory
> > > mappings will raise a userfault.
> > > 
> > > Upon userfault, in order to access memory mappings, if graphics function is in
> > > D3 then runtime resume of dgpu will be triggered to transition to D0.
> > IMO we need a configurable threshold to control the behavior of mmap mappings
> > Invalidation, if vram usages is crosses to certain threshold, disable the runtime PM for
> > entire life time of mapping.
> Agreed. Other option could be disable rpm on server descrete graphics for
> entire life time of mapping. But mainitaning threshold is more promising and
> gives control to user.

what use cases we have here for this?
I believe that for discrete we could entirely block rpm if we have display
or if we have shared dma_buf. any other case we should handle?

> 
> Regards,
> Badal
> > Thanks,
> > Anshuman Gupta
> > > 
> > > Cc: Matthew Auld <matthew.auld@intel.com>
> > > Cc: Anshuman Gupta <anshuman.gupta@intel.com>
> > > Signed-off-by: Badal Nilawar <badal.nilawar@intel.com>
> > > ---
> > >   drivers/gpu/drm/xe/xe_bo.c           | 53 ++++++++++++++++++++++++++--
> > >   drivers/gpu/drm/xe/xe_bo.h           |  2 ++
> > >   drivers/gpu/drm/xe/xe_bo_types.h     |  6 ++++
> > >   drivers/gpu/drm/xe/xe_device_types.h | 20 +++++++++++
> > >   drivers/gpu/drm/xe/xe_pm.c           |  7 ++++
> > >   5 files changed, 85 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/xe/xe_bo.c b/drivers/gpu/drm/xe/xe_bo.c
> > > index 1ab682d61e3c..4192bfcd8013 100644
> > > --- a/drivers/gpu/drm/xe/xe_bo.c
> > > +++ b/drivers/gpu/drm/xe/xe_bo.c
> > > @@ -776,6 +776,18 @@ static int xe_bo_move(struct ttm_buffer_object
> > > *ttm_bo, bool evict,
> > >   		dma_fence_put(fence);
> > >   	}
> > > 
> > > +	/*
> > > +	* TTM has already nuked the mmap for us (see
> > > ttm_bo_unmap_virtual),
> > > +	* so if we moved from VRAM make sure to unlink this from the
> > > userfault
> > > +	* tracking.
> > > +	*/
> > > +	if (mem_type_is_vram(old_mem_type)) {
> > > +		spin_lock(&xe->mem_access.vram_userfault_lock);
> > > +		if (!list_empty(&bo->vram_userfault_link))
> > > +			list_del_init(&bo->vram_userfault_link);
> > > +		spin_unlock(&xe->mem_access.vram_userfault_lock);
> > > +	}
> > > +
> > >   	xe_device_mem_access_put(xe);
> > >   	trace_printk("new_mem->mem_type=%d\n", new_mem-
> > > > mem_type);
> > > 
> > > @@ -1100,6 +1112,8 @@ static vm_fault_t xe_gem_fault(struct vm_fault
> > > *vmf)  {
> > >   	struct ttm_buffer_object *tbo = vmf->vma->vm_private_data;
> > >   	struct drm_device *ddev = tbo->base.dev;
> > > +	struct xe_bo *bo = ttm_to_xe_bo(tbo);
> > > +	struct xe_device *xe = to_xe_device(ddev);
> > >   	vm_fault_t ret;
> > >   	int idx, r = 0;
> > > 
> > > @@ -1107,9 +1121,10 @@ static vm_fault_t xe_gem_fault(struct vm_fault
> > > *vmf)
> > >   	if (ret)
> > >   		return ret;
> > > 
> > > -	if (drm_dev_enter(ddev, &idx)) {
> > > -		struct xe_bo *bo = ttm_to_xe_bo(tbo);
> > > +	if (tbo->resource->bus.is_iomem)
> > > +		xe_device_mem_access_get(xe);
> > > 
> > > +	if (drm_dev_enter(ddev, &idx)) {
> > >   		trace_xe_bo_cpu_fault(bo);
> > > 
> > >   		if (should_migrate_to_system(bo)) {
> > > @@ -1127,10 +1142,25 @@ static vm_fault_t xe_gem_fault(struct vm_fault
> > > *vmf)
> > >   	} else {
> > >   		ret = ttm_bo_vm_dummy_page(vmf, vmf->vma-
> > > > vm_page_prot);
> > >   	}
> > > +
> > >   	if (ret == VM_FAULT_RETRY && !(vmf->flags &
> > > FAULT_FLAG_RETRY_NOWAIT))
> > > -		return ret;
> > > +		goto out_rpm;
> > > +	/*
> > > +	 * ttm_bo_vm_reserve() already has dma_resv_lock.
> > > +	 * vram_userfault_count is protected by dma_resv lock and rpm
> > > wakeref.
> > > +	 */
> > > +	if (ret == VM_FAULT_NOPAGE &&
> > > xe_device_mem_access_ongoing(xe) && !bo->vram_userfault_count) {
> > > +		bo->vram_userfault_count = 1;
> > > +		spin_lock(&xe->mem_access.vram_userfault_lock);
> > > +		list_add(&bo->vram_userfault_link, &xe-
> > > > mem_access.vram_userfault_list);
> > > +		spin_unlock(&xe->mem_access.vram_userfault_lock);
> > > 
> > > +		XE_WARN_ON(!tbo->resource->bus.is_iomem);
> > > +	}
> > >   	dma_resv_unlock(tbo->base.resv);
> > > +out_rpm:
> > > +	if(tbo->resource->bus.is_iomem &&
> > > xe_device_mem_access_ongoing(xe))
> > > +		xe_device_mem_access_put(xe);
> > >   	return ret;
> > >   }
> > > 
> > > @@ -2108,6 +2138,23 @@ int xe_bo_dumb_create(struct drm_file
> > > *file_priv,
> > >   	return err;
> > >   }
> > > 
> > > +void xe_bo_runtime_pm_release_mmap_offset(struct xe_bo *bo) {
> > > +	struct ttm_buffer_object *tbo = &bo->ttm;
> > > +	struct ttm_device *bdev = tbo->bdev;
> > > +
> > > +	drm_vma_node_unmap(&tbo->base.vma_node, bdev-
> > > > dev_mapping);
> > > +
> > > +	/*
> > > +	 * We have exclusive access here via runtime suspend. All other
> > > callers
> > > +	 * must first grab the rpm wakeref.
> > > +	 */
> > > +	XE_WARN_ON(!bo->vram_userfault_count);
> > > +	list_del(&bo->vram_userfault_link);
> > > +	bo->vram_userfault_count = 0;
> > > +}
> > > +
> > > +
> > >   #if IS_ENABLED(CONFIG_DRM_XE_KUNIT_TEST)
> > >   #include "tests/xe_bo.c"
> > >   #endif
> > > diff --git a/drivers/gpu/drm/xe/xe_bo.h b/drivers/gpu/drm/xe/xe_bo.h
> > > index 0823dda0f31b..6b86f326c700 100644
> > > --- a/drivers/gpu/drm/xe/xe_bo.h
> > > +++ b/drivers/gpu/drm/xe/xe_bo.h
> > > @@ -247,6 +247,8 @@ int xe_gem_create_ioctl(struct drm_device *dev,
> > > void *data,
> > >   			struct drm_file *file);
> > >   int xe_gem_mmap_offset_ioctl(struct drm_device *dev, void *data,
> > >   			     struct drm_file *file);
> > > +void xe_bo_runtime_pm_release_mmap_offset(struct xe_bo *bo);
> > > +
> > >   int xe_bo_dumb_create(struct drm_file *file_priv,
> > >   		      struct drm_device *dev,
> > >   		      struct drm_mode_create_dumb *args); diff --git
> > > a/drivers/gpu/drm/xe/xe_bo_types.h
> > > b/drivers/gpu/drm/xe/xe_bo_types.h
> > > index f6ee920303af..cdca91a378c4 100644
> > > --- a/drivers/gpu/drm/xe/xe_bo_types.h
> > > +++ b/drivers/gpu/drm/xe/xe_bo_types.h
> > > @@ -68,6 +68,12 @@ struct xe_bo {
> > >   	struct llist_node freed;
> > >   	/** @created: Whether the bo has passed initial creation */
> > >   	bool created;
> > > +	/**
> > > +	 * Whether the object is currently in fake offset mmap backed by
> > > vram.
> > > +	 */
> > > +	unsigned int vram_userfault_count;
> > > +	struct list_head vram_userfault_link;
> > > +
> > >   };
> > > 
> > >   #endif
> > > diff --git a/drivers/gpu/drm/xe/xe_device_types.h
> > > b/drivers/gpu/drm/xe/xe_device_types.h
> > > index 750e1f0d3339..c345fb483af1 100644
> > > --- a/drivers/gpu/drm/xe/xe_device_types.h
> > > +++ b/drivers/gpu/drm/xe/xe_device_types.h
> > > @@ -328,6 +328,26 @@ struct xe_device {
> > >   	struct {
> > >   		/** @ref: ref count of memory accesses */
> > >   		atomic_t ref;
> > > +		/*
> > > +		 *  Protects access to vram usefault list.
> > > +		 *  It is required, if we are outside of the runtime suspend
> > > path,
> > > +		 *  access to @vram_userfault_list requires always first
> > > grabbing the
> > > +		 *  runtime pm, to ensure we can't race against runtime
> > > suspend.
> > > +		 *  Once we have that we also need to grab
> > > @vram_userfault_lock,
> > > +		 *  at which point we have exclusive access.
> > > +		 *  The runtime suspend path is special since it doesn't really
> > > hold any locks,
> > > +		 *  but instead has exclusive access by virtue of all other
> > > accesses requiring
> > > +		 *  holding the runtime pm wakeref.
> > > +		 */
> > > +		spinlock_t vram_userfault_lock;
> > > +
> > > +		/*
> > > +		 *  Keep list of userfaulted gem obj, which require to release
> > > their
> > > +		 *  mmap mappings at runtime suspend path.
> > > +		 */
> > > +		struct list_head vram_userfault_list;
> > > +
> > > +		bool vram_userfault_ongoing;
> > >   	} mem_access;
> > > 
> > >   	/** @d3cold: Encapsulate d3cold related stuff */ diff --git
> > > a/drivers/gpu/drm/xe/xe_pm.c b/drivers/gpu/drm/xe/xe_pm.c index
> > > 0f06d8304e17..51cde1db930e 100644
> > > --- a/drivers/gpu/drm/xe/xe_pm.c
> > > +++ b/drivers/gpu/drm/xe/xe_pm.c
> > > @@ -172,6 +172,8 @@ void xe_pm_init(struct xe_device *xe)
> > >   	}
> > > 
> > >   	xe_pm_runtime_init(xe);
> > > +	INIT_LIST_HEAD(&xe->mem_access.vram_userfault_list);
> > > +	spin_lock_init(&xe->mem_access.vram_userfault_lock);
> > >   }
> > > 
> > >   void xe_pm_runtime_fini(struct xe_device *xe) @@ -205,6 +207,7 @@
> > > struct task_struct *xe_pm_read_callback_task(struct xe_device *xe)
> > > 
> > >   int xe_pm_runtime_suspend(struct xe_device *xe)  {
> > > +	struct xe_bo *bo, *on;
> > >   	struct xe_gt *gt;
> > >   	u8 id;
> > >   	int err = 0;
> > > @@ -238,6 +241,10 @@ int xe_pm_runtime_suspend(struct xe_device *xe)
> > >   	 */
> > >   	lock_map_acquire(&xe_device_mem_access_lockdep_map);
> > > 
> > > +	list_for_each_entry_safe(bo, on,
> > > +				 &xe->mem_access.vram_userfault_list,
> > > vram_userfault_link)
> > > +		xe_bo_runtime_pm_release_mmap_offset(bo);
> > > +
> > >   	if (xe->d3cold.allowed) {
> > >   		err = xe_bo_evict_all(xe);
> > >   		if (err)
> > > --
> > > 2.25.1
> >