Re: [PATCH v27 3/4] drm/xe/xe_vm: Add per VM fault info

[Matthew Brost <matthew.brost@intel.com>]

On Mon, Dec 01, 2025 at 05:44:47PM +0000, Jonathan Cavitt wrote:
> Add additional information to each VM so they can report up to the first
> 50 seen faults.  Only pagefaults are saved this way currently, though in
> the future, all faults should be tracked by the VM for future reporting.
> 
> Additionally, of the pagefaults reported, only failed pagefaults are
> saved this way, as successful pagefaults should recover silently and not
> need to be reported to userspace.
> 
> v2:
> - Free vm after use (Shuicheng)
> - Compress pf copy logic (Shuicheng)
> - Update fault_unsuccessful before storing (Shuicheng)
> - Fix old struct name in comments (Shuicheng)
> - Keep first 50 pagefaults instead of last 50 (Jianxun)
> 
> v3:
> - Avoid unnecessary execution by checking MAX_PFS earlier (jcavitt)
> - Fix double-locking error (jcavitt)
> - Assert kmemdump is successful (Shuicheng)
> 
> v4:
> - Rename xe_vm.pfs to xe_vm.faults (jcavitt)
> - Store fault data and not pagefault in xe_vm faults list (jcavitt)
> - Store address, address type, and address precision per fault (jcavitt)
> - Store engine class and instance data per fault (Jianxun)
> - Add and fix kernel docs (Michal W)
> - Properly handle kzalloc error (Michal W)
> - s/MAX_PFS/MAX_FAULTS_SAVED_PER_VM (Michal W)
> - Store fault level per fault (Micahl M)
> 
> v5:
> - Store fault and access type instead of address type (Jianxun)
> 
> v6:
> - Store pagefaults in non-fault-mode VMs as well (Jianxun)
> 
> v7:
> - Fix kernel docs and comments (Michal W)
> 
> v8:
> - Fix double-locking issue (Jianxun)
> 
> v9:
> - Do not report faults from reserved engines (Jianxun)
> 
> v10:
> - Remove engine class and instance (Ivan)
> 
> v11:
> - Perform kzalloc outside of lock (Auld)
> 
> v12:
> - Fix xe_vm_fault_entry kernel docs (Shuicheng)
> 
> v13:
> - Rebase and refactor (jcavitt)
> 
> v14:
> - Correctly ignore fault mode in save_pagefault_to_vm (jcavitt)
> 
> Signed-off-by: Jonathan Cavitt <jonathan.cavitt@intel.com>
> Suggested-by: Matthew Brost <matthew.brost@intel.com>
> Cc: Shuicheng Lin <shuicheng.lin@intel.com>
> Cc: Jianxun Zhang <jianxun.zhang@intel.com>
> Cc: Michal Wajdeczko <Michal.Wajdeczko@intel.com>
> Cc: Michal Mzorek <michal.mzorek@intel.com>
> Cc: Ivan Briano <ivan.briano@intel.com>
> Cc: Matthew Auld <matthew.auld@intel.com>
> ---
>  drivers/gpu/drm/xe/xe_pagefault.c | 26 +++++++++
>  drivers/gpu/drm/xe/xe_vm.c        | 88 +++++++++++++++++++++++++++++++
>  drivers/gpu/drm/xe/xe_vm.h        |  9 ++++
>  drivers/gpu/drm/xe/xe_vm_types.h  | 29 ++++++++++
>  4 files changed, 152 insertions(+)
> 
> diff --git a/drivers/gpu/drm/xe/xe_pagefault.c b/drivers/gpu/drm/xe/xe_pagefault.c
> index 0b625a52a598..5997023a5889 100644
> --- a/drivers/gpu/drm/xe/xe_pagefault.c
> +++ b/drivers/gpu/drm/xe/xe_pagefault.c
> @@ -247,6 +247,31 @@ static void xe_pagefault_print(struct xe_pagefault *pf)
>  		  pf->consumer.engine_instance);
>  }
>  
> +static void save_pagefault_to_vm(struct xe_device *xe, struct xe_pagefault *pf)

Every function in xe_pagefault.c starts with 'xe_pagefault_'

So maybe: s/save_pagefault_to_vm/xe_pagefault_save_to_vm

> +{
> +	struct xe_vm *vm;
> +
> +	/*
> +	 * Pagefault may be asociated to VM that is not in fault mode.
> +	 * Perform asid_to_vm behavior, except if VM is not in fault
> +	 * mode, return VM anyways.
> +	 */
> +	down_read(&xe->usm.lock);
> +	vm = xa_load(&xe->usm.asid_to_vm, pf->consumer.asid);
> +	if (vm)
> +		xe_vm_get(vm);
> +	else
> +		vm = ERR_PTR(-EINVAL);
> +	up_read(&xe->usm.lock);
> +
> +	if (IS_ERR(vm))
> +		return;
> +
> +	xe_vm_add_fault_entry_pf(vm, pf);
> +
> +	xe_vm_put(vm);
> +}
> +
>  static void xe_pagefault_queue_work(struct work_struct *w)
>  {
>  	struct xe_pagefault_queue *pf_queue =
> @@ -266,6 +291,7 @@ static void xe_pagefault_queue_work(struct work_struct *w)
>  		err = xe_pagefault_service(&pf);
>  		if (err) {
>  			xe_pagefault_print(&pf);
> +			save_pagefault_to_vm(gt_to_xe(pf.gt), &pf);
>  			xe_gt_dbg(pf.gt, "Fault response: Unsuccessful %pe\n",
>  				  ERR_PTR(err));
>  		}
> diff --git a/drivers/gpu/drm/xe/xe_vm.c b/drivers/gpu/drm/xe/xe_vm.c
> index 8ab726289583..e69e10233b00 100644
> --- a/drivers/gpu/drm/xe/xe_vm.c
> +++ b/drivers/gpu/drm/xe/xe_vm.c
> @@ -27,6 +27,7 @@
>  #include "xe_device.h"
>  #include "xe_drm_client.h"
>  #include "xe_exec_queue.h"
> +#include "xe_gt.h"
>  #include "xe_migrate.h"
>  #include "xe_pat.h"
>  #include "xe_pm.h"
> @@ -578,6 +579,88 @@ static void preempt_rebind_work_func(struct work_struct *w)
>  	trace_xe_vm_rebind_worker_exit(vm);
>  }
>  
> +static struct xe_hw_engine *
> +hw_engine_lookup_class_instance(struct xe_vm *vm,
> +				enum xe_engine_class class,
> +				u16 instance)

Can we use xe_hw_engine_lookup or xe_gt_hw_engine rather than adding a
new helper?

> +{
> +	struct xe_device *xe = vm->xe;
> +	struct xe_hw_engine *hwe;
> +	enum xe_hw_engine_id id;
> +	struct xe_gt *gt;
> +	u8 gt_id;
> +
> +	for_each_gt(gt, xe, gt_id)
> +		for_each_hw_engine(hwe, gt, id)
> +			if (hwe->class == class && hwe->instance == instance)
> +				return hwe;
> +	return NULL;
> +}
> +
> +/**
> + * xe_vm_add_fault_entry_pf() - Add pagefault to vm fault list
> + * @vm: The VM.
> + * @pf: The pagefault.
> + *
> + * This function takes the data from the pagefault @pf and saves it to @vm->faults.list.
> + *
> + * The function exits silently if the list is full, and reports a warning if the pagefault
> + * could not be saved to the list.
> + */
> +void xe_vm_add_fault_entry_pf(struct xe_vm *vm, struct xe_pagefault *pf)
> +{
> +	struct xe_vm_fault_entry *e = NULL;
> +	struct xe_hw_engine *hwe;
> +
> +	/* Do not report faults on reserved engines */
> +	hwe = hw_engine_lookup_class_instance(vm, pf->consumer.engine_class,
> +					      pf->consumer.engine_instance);
> +	if (!hwe || xe_hw_engine_is_reserved(hwe))
> +		return;
> +
> +	e = kzalloc(sizeof(*e), GFP_KERNEL);
> +	if (!e) {
> +		drm_warn(&vm->xe->drm,
> +			 "Could not allocate memory for fault!\n");
> +		return;
> +	}
> +
> +	spin_lock(&vm->faults.lock);
> +

Michal would say use guard(spinlock)(&vm->faults.lock) here. Probably
a little cleaner as the goto can be avoided.

> +	/*
> +	 * Limit the number of faults in the fault list to prevent
> +	 * memory overuse.
> +	 */
> +	if (vm->faults.len >= MAX_FAULTS_SAVED_PER_VM) {
> +		kfree(e);
> +		goto out;
> +	}
> +
> +	e->address = pf->consumer.page_addr;
> +	e->address_precision = 1;
> +	e->access_type = pf->consumer.access_type;
> +	e->fault_type = pf->consumer.fault_type;
> +	e->fault_level = pf->consumer.fault_level;
> +
> +	list_add_tail(&e->list, &vm->faults.list);
> +	vm->faults.len++;
> +out:
> +	spin_unlock(&vm->faults.lock);
> +}
> +
> +static void xe_vm_clear_fault_entries(struct xe_vm *vm)
> +{
> +	struct xe_vm_fault_entry *e, *tmp;
> +
> +	spin_lock(&vm->faults.lock);

Probably a guard here too.

Nits aside, overall LGTM.

Matt

> +	list_for_each_entry_safe(e, tmp, &vm->faults.list, list) {
> +		list_del(&e->list);
> +		kfree(e);
> +	}
> +	vm->faults.len = 0;
> +	spin_unlock(&vm->faults.lock);
> +}
> +
>  static int xe_vma_ops_alloc(struct xe_vma_ops *vops, bool array_of_binds)
>  {
>  	int i;
> @@ -1503,6 +1586,9 @@ struct xe_vm *xe_vm_create(struct xe_device *xe, u32 flags, struct xe_file *xef)
>  	INIT_LIST_HEAD(&vm->userptr.invalidated);
>  	spin_lock_init(&vm->userptr.invalidated_lock);
>  
> +	INIT_LIST_HEAD(&vm->faults.list);
> +	spin_lock_init(&vm->faults.lock);
> +
>  	ttm_lru_bulk_move_init(&vm->lru_bulk_move);
>  
>  	INIT_WORK(&vm->destroy_work, vm_destroy_work_func);
> @@ -1808,6 +1894,8 @@ void xe_vm_close_and_put(struct xe_vm *vm)
>  	}
>  	up_write(&xe->usm.lock);
>  
> +	xe_vm_clear_fault_entries(vm);
> +
>  	for_each_tile(tile, xe, id)
>  		xe_range_fence_tree_fini(&vm->rftree[id]);
>  
> diff --git a/drivers/gpu/drm/xe/xe_vm.h b/drivers/gpu/drm/xe/xe_vm.h
> index 361f10b3c453..e9f2de4189e0 100644
> --- a/drivers/gpu/drm/xe/xe_vm.h
> +++ b/drivers/gpu/drm/xe/xe_vm.h
> @@ -12,6 +12,12 @@
>  #include "xe_map.h"
>  #include "xe_vm_types.h"
>  
> +/**
> + * MAX_FAULTS_SAVED_PER_VM - Maximum number of faults each vm can store before future
> + * faults are discarded to prevent memory overuse
> + */
> +#define MAX_FAULTS_SAVED_PER_VM	50
> +
>  struct drm_device;
>  struct drm_printer;
>  struct drm_file;
> @@ -22,6 +28,7 @@ struct dma_fence;
>  
>  struct xe_exec_queue;
>  struct xe_file;
> +struct xe_pagefault;
>  struct xe_sync_entry;
>  struct xe_svm_range;
>  struct drm_exec;
> @@ -309,6 +316,8 @@ void xe_vm_snapshot_capture_delayed(struct xe_vm_snapshot *snap);
>  void xe_vm_snapshot_print(struct xe_vm_snapshot *snap, struct drm_printer *p);
>  void xe_vm_snapshot_free(struct xe_vm_snapshot *snap);
>  
> +void xe_vm_add_fault_entry_pf(struct xe_vm *vm, struct xe_pagefault *pf);
> +
>  /**
>   * xe_vm_set_validating() - Register this task as currently making bos resident
>   * @allow_res_evict: Allow eviction of buffer objects bound to @vm when
> diff --git a/drivers/gpu/drm/xe/xe_vm_types.h b/drivers/gpu/drm/xe/xe_vm_types.h
> index 3bf912bfbdcc..fff914fb0aa6 100644
> --- a/drivers/gpu/drm/xe/xe_vm_types.h
> +++ b/drivers/gpu/drm/xe/xe_vm_types.h
> @@ -20,6 +20,7 @@
>  #include "xe_userptr.h"
>  
>  struct xe_bo;
> +struct xe_pagefault;
>  struct xe_svm_range;
>  struct xe_sync_entry;
>  struct xe_user_fence;
> @@ -165,6 +166,24 @@ struct xe_userptr_vma {
>  
>  struct xe_device;
>  
> +/**
> + * struct xe_vm_fault_entry - Elements of vm->faults.list
> + * @list: link into @xe_vm.faults.list
> + * @address: address of the fault
> + * @address_precision: precision of faulted address
> + * @access_type: type of address access that resulted in fault
> + * @fault_type: type of fault reported
> + * @fault_level: fault level of the fault
> + */
> +struct xe_vm_fault_entry {
> +	struct list_head list;
> +	u64 address;
> +	u32 address_precision;
> +	u8 access_type;
> +	u8 fault_type;
> +	u8 fault_level;
> +};
> +
>  struct xe_vm {
>  	/** @gpuvm: base GPUVM used to track VMAs */
>  	struct drm_gpuvm gpuvm;
> @@ -302,6 +321,16 @@ struct xe_vm {
>  		bool capture_once;
>  	} error_capture;
>  
> +	/** @faults: List of all faults associated with this VM */
> +	struct {
> +		/** @faults.lock: lock protecting @faults.list */
> +		spinlock_t lock;
> +		/** @faults.list: list of xe_vm_fault_entry entries */
> +		struct list_head list;
> +		/** @faults.len: length of @faults.list */
> +		unsigned int len;
> +	} faults;
> +
>  	/**
>  	 * @validation: Validation data only valid with the vm resv held.
>  	 * Note: This is really task state of the task holding the vm resv,
> -- 
> 2.43.0
>