RE: [PATCH v4 01/30] drm/xe: Lock all gpuva ops during VM bind IOCTL

["Zeng, Oak" <oak.zeng@intel.com>]

> -----Original Message-----
> From: Intel-xe <intel-xe-bounces@lists.freedesktop.org> On Behalf Of Matthew
> Brost
> Sent: Friday, March 8, 2024 12:08 AM
> To: intel-xe@lists.freedesktop.org
> Cc: Brost, Matthew <matthew.brost@intel.com>
> Subject: [PATCH v4 01/30] drm/xe: Lock all gpuva ops during VM bind IOCTL
> 
> Lock all gpuva ops

Can we have a better wording? Better to say locking all Bos used in gpuva ops? 

Or maybe lock ops by locking and validating all Bos used in ops.

 and validate all BOs in a single step durin the VM
> bind IOCTL. This help with the transition to making all gpuva ops in a
> VM bind IOCTL a single atomic job.

Can you also explain, why you want bind to be a atomic job? 

My guess is, bind ioctl can end up with a series of operations, if some (not all) of those operations fail in the middle, it is hard to revert the successful operations before failure. 
> 
> Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> ---
>  drivers/gpu/drm/xe/xe_vm.c | 142 ++++++++++++++++++++++++++-----------
>  1 file changed, 101 insertions(+), 41 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_vm.c b/drivers/gpu/drm/xe/xe_vm.c
> index 643b3701a738..3b5dc6de07f7 100644
> --- a/drivers/gpu/drm/xe/xe_vm.c
> +++ b/drivers/gpu/drm/xe/xe_vm.c
> @@ -413,19 +413,23 @@ int __xe_vm_userptr_needs_repin(struct xe_vm *vm)
> 
>  #define XE_VM_REBIND_RETRY_TIMEOUT_MS 1000
> 
> -static void xe_vm_kill(struct xe_vm *vm)
> +static void xe_vm_kill(struct xe_vm *vm, bool unlocked)
>  {
>  	struct xe_exec_queue *q;
> 
>  	lockdep_assert_held(&vm->lock);
> 
> -	xe_vm_lock(vm, false);
> +	if (unlocked)
> +		xe_vm_lock(vm, false);
> +

Can you explain why we need xe_vm_lock in the first place here? 

My understanding is, xe_vm_lock protect gpu page table update. Below kill function eventually calls into guc_exec_queue_kill where I don't see any page table operation there. So I doubt whether we need the lock in the first place.

>  	vm->flags |= XE_VM_FLAG_BANNED;
>  	trace_xe_vm_kill(vm);
> 
>  	list_for_each_entry(q, &vm->preempt.exec_queues, compute.link)
>  		q->ops->kill(q);
> -	xe_vm_unlock(vm);
> +
> +	if (unlocked)
> +		xe_vm_unlock(vm);
> 
>  	/* TODO: Inform user the VM is banned */
>  }
> @@ -621,7 +625,7 @@ static void preempt_rebind_work_func(struct work_struct
> *w)
> 
>  	if (err) {
>  		drm_warn(&vm->xe->drm, "VM worker error: %d\n", err);
> -		xe_vm_kill(vm);
> +		xe_vm_kill(vm, true);
>  	}
>  	up_write(&vm->lock);
> 
> @@ -1831,17 +1835,9 @@ static int xe_vm_bind(struct xe_vm *vm, struct xe_vma
> *vma, struct xe_exec_queue
>  		      u32 num_syncs, bool immediate, bool first_op,
>  		      bool last_op)
>  {
> -	int err;
> -
>  	xe_vm_assert_held(vm);
>  	xe_bo_assert_held(bo);
> 
> -	if (bo && immediate) {
> -		err = xe_bo_validate(bo, vm, true);
> -		if (err)
> -			return err;
> -	}
> -
>  	return __xe_vm_bind(vm, vma, q, syncs, num_syncs, immediate, first_op,
>  			    last_op);
>  }
> @@ -2488,17 +2484,12 @@ static int vm_bind_ioctl_ops_parse(struct xe_vm *vm,
> struct xe_exec_queue *q,
>  	return 0;
>  }
> 
> -static int op_execute(struct drm_exec *exec, struct xe_vm *vm,
> -		      struct xe_vma *vma, struct xe_vma_op *op)
> +static int op_execute(struct xe_vm *vm, struct xe_vma *vma,
> +		      struct xe_vma_op *op)
>  {
>  	int err;
> 
>  	lockdep_assert_held_write(&vm->lock);
> -
> -	err = xe_vm_prepare_vma(exec, vma, 1);
> -	if (err)
> -		return err;
> -
>  	xe_vm_assert_held(vm);
>  	xe_bo_assert_held(xe_vma_bo(vma));
> 
> @@ -2579,19 +2570,10 @@ static int op_execute(struct drm_exec *exec, struct
> xe_vm *vm,
>  static int __xe_vma_op_execute(struct xe_vm *vm, struct xe_vma *vma,
>  			       struct xe_vma_op *op)
>  {
> -	struct drm_exec exec;
>  	int err;
> 
>  retry_userptr:
> -	drm_exec_init(&exec, DRM_EXEC_INTERRUPTIBLE_WAIT, 0);
> -	drm_exec_until_all_locked(&exec) {
> -		err = op_execute(&exec, vm, vma, op);
> -		drm_exec_retry_on_contention(&exec);
> -		if (err)
> -			break;
> -	}
> -	drm_exec_fini(&exec);
> -
> +	err = op_execute(vm, vma, op);
>  	if (err == -EAGAIN) {
>  		lockdep_assert_held_write(&vm->lock);
> 
> @@ -2756,29 +2738,107 @@ static void vm_bind_ioctl_ops_unwind(struct xe_vm
> *vm,
>  	}
>  }
> 
> +static int vma_lock(struct drm_exec *exec, struct xe_vma *vma, bool validate)
> +{
> +	struct xe_bo *bo = xe_vma_bo(vma);
> +	int err = 0;
> +
> +	if (bo) {
> +		if (!bo->vm)
> +			err = drm_exec_prepare_obj(exec, &bo->ttm.base, 1);
> +		if (!err && validate)
> +			err = xe_bo_validate(bo, xe_vma_vm(vma), true);
> +	}
> +
> +	return err;
> +}
> +
> +static int op_lock(struct drm_exec *exec, struct xe_vm *vm,
> +		   struct xe_vma_op *op)
> +{
> +	int err = 0;
> +
> +	switch (op->base.op) {
> +	case DRM_GPUVA_OP_MAP:
> +		err = vma_lock(exec, op->map.vma, !xe_vm_in_fault_mode(vm));
> +		break;
> +	case DRM_GPUVA_OP_REMAP:
> +		err = vma_lock(exec, gpuva_to_vma(op->base.remap.unmap->va),
> +			       false);
> +		if (!err && op->remap.prev)
> +			err = vma_lock(exec, op->remap.prev, true);
> +		if (!err && op->remap.next)
> +			err = vma_lock(exec, op->remap.next, true);
> +		break;
> +	case DRM_GPUVA_OP_UNMAP:
> +		err = vma_lock(exec, gpuva_to_vma(op->base.unmap.va), false);
> +		break;
> +	case DRM_GPUVA_OP_PREFETCH:
> +		err = vma_lock(exec, gpuva_to_vma(op->base.prefetch.va), true);
> +		break;
> +	default:
> +		drm_warn(&vm->xe->drm, "NOT POSSIBLE");
> +	}
> +
> +	return err;
> +}
> +
> +static int vm_bind_ioctl_ops_lock(struct drm_exec *exec,
> +				  struct xe_vm *vm,
> +				  struct list_head *ops_list)
> +{
> +	struct xe_vma_op *op;
> +	int err;
> +
> +	err = drm_exec_prepare_obj(exec, xe_vm_obj(vm), 1);
> +	if (err)
> +		return err;
> +
> +	list_for_each_entry(op, ops_list, link) {
> +		err = op_lock(exec, vm, op);
> +		if (err)
> +			return err;
> +	}
> +
> +	return 0;
> +}
> +
>  static int vm_bind_ioctl_ops_execute(struct xe_vm *vm,
>  				     struct list_head *ops_list)
>  {
> +	struct drm_exec exec;
>  	struct xe_vma_op *op, *next;
>  	int err;
> 
>  	lockdep_assert_held_write(&vm->lock);
> 
> -	list_for_each_entry_safe(op, next, ops_list, link) {
> -		err = xe_vma_op_execute(vm, op);
> -		if (err) {
> -			drm_warn(&vm->xe->drm, "VM op(%d) failed with %d",
> -				 op->base.op, err);
> -			/*
> -			 * FIXME: Killing VM rather than proper error handling
> -			 */
> -			xe_vm_kill(vm);
> -			return -ENOSPC;
> +	drm_exec_init(&exec, DRM_EXEC_INTERRUPTIBLE_WAIT |
> +		      DRM_EXEC_IGNORE_DUPLICATES, 0);
> +	drm_exec_until_all_locked(&exec) {
> +		err = vm_bind_ioctl_ops_lock(&exec, vm, ops_list);
> +		drm_exec_retry_on_contention(&exec);
> +		if (err)
> +			goto unlock;
> +

Do you need below ops inside the drm_exec_until_all_locked loop? After you locked all objects, you can close the drm_exec_until_all_locked loop, then perform below out of drm_exec_until_all_locked loop. 

Oak 

> +		list_for_each_entry_safe(op, next, ops_list, link) {
> +			err = xe_vma_op_execute(vm, op);
> +			if (err) {
> +				drm_warn(&vm->xe->drm, "VM op(%d) failed
> with %d",
> +					 op->base.op, err);
> +				/*
> +				 * FIXME: Killing VM rather than proper error
> handling
> +				 */
> +				xe_vm_kill(vm, false);
> +				err = -ENOSPC;
> +				goto unlock;
> +			}
> +			xe_vma_op_cleanup(vm, op);
>  		}
> -		xe_vma_op_cleanup(vm, op);
>  	}
> 
> -	return 0;
> +unlock:
> +	drm_exec_fini(&exec);
> +	return err;
>  }
> 
>  #define SUPPORTED_FLAGS	(DRM_XE_VM_BIND_FLAG_NULL | \
> --
> 2.34.1