Re: [PATCH] drm/xe/uapi: Introduce a flag to disallow vm overcommit in fault mode

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

On Wed, Feb 04, 2026 at 04:33:20PM +0100, Thomas Hellström wrote:
> Some compute applications may try to allocate device memory to probe
> how much device memory is actually available, assuming that the
> application will be the only one running on the particular GPU.
> 
> That strategy fails in fault mode since it allows VM overcommit.
> 
> While this could be resolved in user-space it's further complicated
> by cgroups potentially restricting the amount of memory available
> to the application.
> 
> Introduce a vm create flag, DRM_XE_VM_CREATE_NO_VM_OVERCOMMIT, that
> allows fault mode to mimic the behaviour of !fault mode WRT this. It
> blocks evicting same vm bos during VM_BIND processing. However,
> it does *not* block evicting same-vm bos during pagefault
> processing, preferring eviction rather than VM banning in
> OOM situations.
> 
> Cc: John Falkowski <john.falkowski@intel.com>
> Cc: Michal Mrozek <michal.mrozek@intel.com>
> Cc: Matthew Brost <matthew.brost@intel.com>
> Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> ---
>  drivers/gpu/drm/xe/xe_vm.c       | 11 +++++++++--
>  drivers/gpu/drm/xe/xe_vm.h       |  7 +++++++
>  drivers/gpu/drm/xe/xe_vm_types.h |  1 +
>  include/uapi/drm/xe_drm.h        |  6 ++++++
>  4 files changed, 23 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_vm.c b/drivers/gpu/drm/xe/xe_vm.c
> index 8fe54a998385..cf92b6e13a16 100644
> --- a/drivers/gpu/drm/xe/xe_vm.c
> +++ b/drivers/gpu/drm/xe/xe_vm.c
> @@ -1938,7 +1938,8 @@ find_ufence_get(struct xe_sync_entry *syncs, u32 num_syncs)
>  
>  #define ALL_DRM_XE_VM_CREATE_FLAGS (DRM_XE_VM_CREATE_FLAG_SCRATCH_PAGE | \
>  				    DRM_XE_VM_CREATE_FLAG_LR_MODE | \
> -				    DRM_XE_VM_CREATE_FLAG_FAULT_MODE)
> +				    DRM_XE_VM_CREATE_FLAG_FAULT_MODE | \
> +				    DRM_XE_VM_CREATE_FLAG_NO_VM_OVERCOMMIT)
>  
>  int xe_vm_create_ioctl(struct drm_device *dev, void *data,
>  		       struct drm_file *file)
> @@ -1977,12 +1978,18 @@ int xe_vm_create_ioctl(struct drm_device *dev, void *data,
>  			 args->flags & DRM_XE_VM_CREATE_FLAG_FAULT_MODE))
>  		return -EINVAL;
>  
> +	if (XE_IOCTL_DBG(xe, !(args->flags & DRM_XE_VM_CREATE_FLAG_FAULT_MODE) &&
> +			 args->flags & DRM_XE_VM_CREATE_FLAG_NO_VM_OVERCOMMIT))
> +		return -EINVAL;
> +
>  	if (args->flags & DRM_XE_VM_CREATE_FLAG_SCRATCH_PAGE)
>  		flags |= XE_VM_FLAG_SCRATCH_PAGE;
>  	if (args->flags & DRM_XE_VM_CREATE_FLAG_LR_MODE)
>  		flags |= XE_VM_FLAG_LR_MODE;
>  	if (args->flags & DRM_XE_VM_CREATE_FLAG_FAULT_MODE)
>  		flags |= XE_VM_FLAG_FAULT_MODE;
> +	if (args->flags & DRM_XE_VM_CREATE_FLAG_NO_VM_OVERCOMMIT)
> +		flags |= XE_VM_FLAG_NO_VM_OVERCOMMIT;
>  
>  	vm = xe_vm_create(xe, flags, xef);
>  	if (IS_ERR(vm))
> @@ -2903,7 +2910,7 @@ static int vma_lock_and_validate(struct drm_exec *exec, struct xe_vma *vma,
>  			err = drm_exec_lock_obj(exec, &bo->ttm.base);
>  		if (!err && validate)
>  			err = xe_bo_validate(bo, vm,
> -					     !xe_vm_in_preempt_fence_mode(vm) &&
> +					     xe_vm_allow_vm_eviction(vm) &&

One question. This is existing code but can you refresh my memory why we
allow overcommit on dma-fencing VMs? Wouldn't the next exec IOCTL
immediately fail?

Matt

>  					     res_evict, exec);
>  	}
>  
> diff --git a/drivers/gpu/drm/xe/xe_vm.h b/drivers/gpu/drm/xe/xe_vm.h
> index 288115c7844a..f849e369432b 100644
> --- a/drivers/gpu/drm/xe/xe_vm.h
> +++ b/drivers/gpu/drm/xe/xe_vm.h
> @@ -220,6 +220,13 @@ static inline bool xe_vm_in_preempt_fence_mode(struct xe_vm *vm)
>  	return xe_vm_in_lr_mode(vm) && !xe_vm_in_fault_mode(vm);
>  }
>  
> +static inline bool xe_vm_allow_vm_eviction(struct xe_vm *vm)
> +{
> +	return !xe_vm_in_lr_mode(vm) ||
> +		(xe_vm_in_fault_mode(vm) &&
> +		 !(vm->flags & XE_VM_FLAG_NO_VM_OVERCOMMIT));
> +}
> +
>  int xe_vm_add_compute_exec_queue(struct xe_vm *vm, struct xe_exec_queue *q);
>  void xe_vm_remove_compute_exec_queue(struct xe_vm *vm, struct xe_exec_queue *q);
>  
> diff --git a/drivers/gpu/drm/xe/xe_vm_types.h b/drivers/gpu/drm/xe/xe_vm_types.h
> index 43203e90ee3e..1f6f7e30e751 100644
> --- a/drivers/gpu/drm/xe/xe_vm_types.h
> +++ b/drivers/gpu/drm/xe/xe_vm_types.h
> @@ -232,6 +232,7 @@ struct xe_vm {
>  #define XE_VM_FLAG_TILE_ID(flags)	FIELD_GET(GENMASK(7, 6), flags)
>  #define XE_VM_FLAG_SET_TILE_ID(tile)	FIELD_PREP(GENMASK(7, 6), (tile)->id)
>  #define XE_VM_FLAG_GSC			BIT(8)
> +#define XE_VM_FLAG_NO_VM_OVERCOMMIT     BIT(9)
>  	unsigned long flags;
>  
>  	/**
> diff --git a/include/uapi/drm/xe_drm.h b/include/uapi/drm/xe_drm.h
> index 077e66a682e2..e54f8e12acd9 100644
> --- a/include/uapi/drm/xe_drm.h
> +++ b/include/uapi/drm/xe_drm.h
> @@ -975,6 +975,11 @@ struct drm_xe_gem_mmap_offset {
>   *    demand when accessed, and also allows per-VM overcommit of memory.
>   *    The xe driver internally uses recoverable pagefaults to implement
>   *    this.
> + *  - %DRM_XE_VM_CREATE_FLAG_NO_VM_OVERCOMMIT - Requires also
> + *    DRM_XE_VM_CREATE_FLAG_FAULT_MODE. This disallows per-VM overcommit
> + *    but only during a &DRM_IOCTL_XE_VM_BIND operation with the
> + *    %DRM_XE_VM_BIND_FLAG_IMMEDIATE flag set. This may be useful for
> + *    user-space naively probing the amount of available memory.
>   */
>  struct drm_xe_vm_create {
>  	/** @extensions: Pointer to the first extension struct, if any */
> @@ -983,6 +988,7 @@ struct drm_xe_vm_create {
>  #define DRM_XE_VM_CREATE_FLAG_SCRATCH_PAGE	(1 << 0)
>  #define DRM_XE_VM_CREATE_FLAG_LR_MODE	        (1 << 1)
>  #define DRM_XE_VM_CREATE_FLAG_FAULT_MODE	(1 << 2)
> +#define DRM_XE_VM_CREATE_FLAG_NO_VM_OVERCOMMIT  (1 << 3)
>  	/** @flags: Flags */
>  	__u32 flags;
>  
> -- 
> 2.52.0
>