[PATCH] drm/xe: Restrict user fences to long running VMs

[Thomas Hellström]

Hi,

On Mon, 2024-06-03 at 10:53 -0700, Matthew Brost wrote:
> User fences are intended to be used on long running VMs, enforce this
> restriction. This addresses possible concerns of using user fences in
> dma-fence and having the dma-fence signal before the user fence.

As mentioned in a separate thread, We should not introduce an uAPI
change with the above motivation. We need to discuss potential use-
cases for !LR vms and if there are found to be none, we could consider
restricting in this way.

/Thomas


> 
> Fixes: d1df9bfbf68c ("drm/xe: Only allow 1 ufence per exec / bind
> IOCTL")
> Fixes: dd08ebf6c352 ("drm/xe: Introduce a new DRM driver for Intel
> GPUs")
> Cc: Thomas Hellström <thomas.hellstrom at linux.intel.com>
> Cc: stable at vger.kernel.org
> Signed-off-by: Matthew Brost <matthew.brost at intel.com>
> ---
>  drivers/gpu/drm/xe/xe_exec.c | 3 ++-
>  drivers/gpu/drm/xe/xe_vm.c   | 3 ++-
>  2 files changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_exec.c
> b/drivers/gpu/drm/xe/xe_exec.c
> index 97eeb973e897..a145813ad229 100644
> --- a/drivers/gpu/drm/xe/xe_exec.c
> +++ b/drivers/gpu/drm/xe/xe_exec.c
> @@ -168,7 +168,8 @@ int xe_exec_ioctl(struct drm_device *dev, void
> *data, struct drm_file *file)
>  			num_ufence++;
>  	}
>  
> -	if (XE_IOCTL_DBG(xe, num_ufence > 1)) {
> +	if (XE_IOCTL_DBG(xe, num_ufence > 1) ||
> +	    XE_IOCTL_DBG(xe, num_ufence && !xe_vm_in_lr_mode(vm))) {
>  		err = -EINVAL;
>  		goto err_syncs;
>  	}
> diff --git a/drivers/gpu/drm/xe/xe_vm.c b/drivers/gpu/drm/xe/xe_vm.c
> index 26b409e1b0f0..85da3a8a83b6 100644
> --- a/drivers/gpu/drm/xe/xe_vm.c
> +++ b/drivers/gpu/drm/xe/xe_vm.c
> @@ -3226,7 +3226,8 @@ int xe_vm_bind_ioctl(struct drm_device *dev,
> void *data, struct drm_file *file)
>  			num_ufence++;
>  	}
>  
> -	if (XE_IOCTL_DBG(xe, num_ufence > 1)) {
> +	if (XE_IOCTL_DBG(xe, num_ufence > 1) ||
> +	    XE_IOCTL_DBG(xe, num_ufence && !xe_vm_in_lr_mode(vm))) {
>  		err = -EINVAL;
>  		goto free_syncs;
>  	}