Re: [PATCH v8 02/12] drm/xe: Allow prefetch-only VM bind IOCTLs to use VM read lock

[Francois Dugast <francois.dugast@intel.com>]

On Fri, Jul 24, 2026 at 04:25:51PM -0700, Matthew Brost wrote:
> Prefetch-only VM bind IOCTLs do not modify VMAs or use userptr pages.
> Downgrade vm->lock to read mode once setup is complete.
> 
> Lays the groundwork for prefetch IOCTLs to use threaded migration.
> 
> Signed-off-by: Matthew Brost <matthew.brost@intel.com>

Reviewed-by: Francois Dugast <francois.dugast@intel.com>

> ---
>  drivers/gpu/drm/xe/xe_vm.c       | 36 +++++++++++++++++++++++++++-----
>  drivers/gpu/drm/xe/xe_vm_types.h |  2 ++
>  2 files changed, 33 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_vm.c b/drivers/gpu/drm/xe/xe_vm.c
> index c064bff842fd..d7e6644df4bc 100644
> --- a/drivers/gpu/drm/xe/xe_vm.c
> +++ b/drivers/gpu/drm/xe/xe_vm.c
> @@ -2451,10 +2451,12 @@ vm_bind_ioctl_ops_create(struct xe_vm *vm, struct xe_vma_ops *vops,
>  			.map.gem.offset = bo_offset_or_userptr,
>  		};
>  
> +		vops->flags |= XE_VMA_OPS_FLAG_MODIFIES_GPUVA;
>  		ops = drm_gpuvm_sm_map_ops_create(&vm->gpuvm, &map_req);
>  		break;
>  	}
>  	case DRM_XE_VM_BIND_OP_UNMAP:
> +		vops->flags |= XE_VMA_OPS_FLAG_MODIFIES_GPUVA;
>  		ops = drm_gpuvm_sm_unmap_ops_create(&vm->gpuvm, addr, range);
>  		break;
>  	case DRM_XE_VM_BIND_OP_PREFETCH:
> @@ -2463,6 +2465,7 @@ vm_bind_ioctl_ops_create(struct xe_vm *vm, struct xe_vma_ops *vops,
>  	case DRM_XE_VM_BIND_OP_UNMAP_ALL:
>  		xe_assert(vm->xe, bo);
>  
> +		vops->flags |= XE_VMA_OPS_FLAG_MODIFIES_GPUVA;
>  		err = xe_bo_lock(bo, true);
>  		if (err)
>  			return ERR_PTR(err);
> @@ -2523,6 +2526,9 @@ vm_bind_ioctl_ops_create(struct xe_vm *vm, struct xe_vma_ops *vops,
>  			u8 id, tile_mask = 0;
>  			u32 i;
>  
> +			if (xe_vma_is_userptr(vma))
> +				vops->flags |= XE_VMA_OPS_FLAG_MODIFIES_GPUVA;
> +
>  			if (!xe_vma_is_cpu_addr_mirror(vma)) {
>  				op->prefetch.region = prefetch_region;
>  				continue;
> @@ -2708,10 +2714,12 @@ static int xe_vma_op_commit(struct xe_vm *vm, struct xe_vma_op *op)
>  {
>  	int err = 0;
>  
> -	xe_vm_assert_write_mode_or_garbage_collector(vm);
> +	lockdep_assert_held(&vm->lock);
>  
>  	switch (op->base.op) {
>  	case DRM_GPUVA_OP_MAP:
> +		xe_vm_assert_write_mode_or_garbage_collector(vm);
> +
>  		err |= xe_vm_insert_vma(vm, op->map.vma);
>  		if (!err)
>  			op->flags |= XE_VMA_OP_COMMITTED;
> @@ -2721,6 +2729,8 @@ static int xe_vma_op_commit(struct xe_vm *vm, struct xe_vma_op *op)
>  		u8 tile_present =
>  			gpuva_to_vma(op->base.remap.unmap->va)->tile_present;
>  
> +		xe_vm_assert_write_mode_or_garbage_collector(vm);
> +
>  		prep_vma_destroy(vm, gpuva_to_vma(op->base.remap.unmap->va),
>  				 true);
>  		op->flags |= XE_VMA_OP_COMMITTED;
> @@ -2755,6 +2765,8 @@ static int xe_vma_op_commit(struct xe_vm *vm, struct xe_vma_op *op)
>  		break;
>  	}
>  	case DRM_GPUVA_OP_UNMAP:
> +		xe_vm_assert_write_mode_or_garbage_collector(vm);
> +
>  		prep_vma_destroy(vm, gpuva_to_vma(op->base.unmap.va), true);
>  		op->flags |= XE_VMA_OP_COMMITTED;
>  		break;
> @@ -2979,10 +2991,12 @@ static void xe_vma_op_unwind(struct xe_vm *vm, struct xe_vma_op *op,
>  			     bool post_commit, bool prev_post_commit,
>  			     bool next_post_commit)
>  {
> -	xe_vm_assert_write_mode_or_garbage_collector(vm);
> +	lockdep_assert_held(&vm->lock);
>  
>  	switch (op->base.op) {
>  	case DRM_GPUVA_OP_MAP:
> +		xe_vm_assert_write_mode_or_garbage_collector(vm);
> +
>  		if (op->map.vma) {
>  			prep_vma_destroy(vm, op->map.vma, post_commit);
>  			xe_vma_destroy_unlocked(op->map.vma);
> @@ -2992,6 +3006,8 @@ static void xe_vma_op_unwind(struct xe_vm *vm, struct xe_vma_op *op,
>  	{
>  		struct xe_vma *vma = gpuva_to_vma(op->base.unmap.va);
>  
> +		xe_vm_assert_write_mode_or_garbage_collector(vm);
> +
>  		if (vma) {
>  			xe_svm_notifier_lock(vm);
>  			vma->gpuva.flags &= ~XE_VMA_DESTROYED;
> @@ -3005,6 +3021,8 @@ static void xe_vma_op_unwind(struct xe_vm *vm, struct xe_vma_op *op,
>  	{
>  		struct xe_vma *vma = gpuva_to_vma(op->base.remap.unmap->va);
>  
> +		xe_vm_assert_write_mode_or_garbage_collector(vm);
> +
>  		if (op->remap.prev) {
>  			prep_vma_destroy(vm, op->remap.prev, prev_post_commit);
>  			xe_vma_destroy_unlocked(op->remap.prev);
> @@ -3589,7 +3607,7 @@ static struct dma_fence *vm_bind_ioctl_ops_execute(struct xe_vm *vm,
>  	struct dma_fence *fence;
>  	int err = 0;
>  
> -	lockdep_assert_held_write(&vm->lock);
> +	lockdep_assert_held(&vm->lock);
>  
>  	xe_validation_guard(&ctx, &vm->xe->val, &exec,
>  			    ((struct xe_val_flags) {
> @@ -3912,7 +3930,7 @@ int xe_vm_bind_ioctl(struct drm_device *dev, void *data, struct drm_file *file)
>  	u32 num_syncs, num_ufence = 0;
>  	struct xe_sync_entry *syncs = NULL;
>  	struct drm_xe_vm_bind_op *bind_ops = NULL;
> -	struct xe_vma_ops vops;
> +	struct xe_vma_ops vops = { .flags = 0, };
>  	struct dma_fence *fence;
>  	int err;
>  	int i;
> @@ -4087,6 +4105,11 @@ int xe_vm_bind_ioctl(struct drm_device *dev, void *data, struct drm_file *file)
>  		goto unwind_ops;
>  	}
>  
> +	if (!(vops.flags & XE_VMA_OPS_FLAG_MODIFIES_GPUVA)) {
> +		vops.flags |= XE_VMA_OPS_FLAG_DOWNGRADE_LOCK;
> +		downgrade_write(&vm->lock);
> +	}
> +
>  	err = xe_vma_ops_alloc(&vops, args->num_binds > 1);
>  	if (err)
>  		goto unwind_ops;
> @@ -4123,7 +4146,10 @@ int xe_vm_bind_ioctl(struct drm_device *dev, void *data, struct drm_file *file)
>  free_bos:
>  	kvfree(bos);
>  release_vm_lock:
> -	up_write(&vm->lock);
> +	if (vops.flags & XE_VMA_OPS_FLAG_DOWNGRADE_LOCK)
> +		up_read(&vm->lock);
> +	else
> +		up_write(&vm->lock);
>  put_exec_queue:
>  	if (q)
>  		xe_exec_queue_put(q);
> diff --git a/drivers/gpu/drm/xe/xe_vm_types.h b/drivers/gpu/drm/xe/xe_vm_types.h
> index b94eb018d532..2f5f74fed9d2 100644
> --- a/drivers/gpu/drm/xe/xe_vm_types.h
> +++ b/drivers/gpu/drm/xe/xe_vm_types.h
> @@ -561,6 +561,8 @@ struct xe_vma_ops {
>  #define XE_VMA_OPS_ARRAY_OF_BINDS	 BIT(2)
>  #define XE_VMA_OPS_FLAG_SKIP_TLB_WAIT	 BIT(3)
>  #define XE_VMA_OPS_FLAG_ALLOW_SVM_UNMAP  BIT(4)
> +#define XE_VMA_OPS_FLAG_MODIFIES_GPUVA	 BIT(5)
> +#define XE_VMA_OPS_FLAG_DOWNGRADE_LOCK	 BIT(6)
>  	u32 flags;
>  #ifdef TEST_VM_OPS_ERROR
>  	/** @inject_error: inject error to test error handling */
> -- 
> 2.34.1
>