Re: [PATCH v2 1/1] cxl/region: Add a region sysfs interface for region lock status

[Alison Schofield]

On Wed, Apr 01, 2026 at 08:49:51PM +0800, Li Ming wrote:
> If a region is created on a root decoder with Fixed Device Confiuration
> attribute, the region will be locked, meaning region destroy
> operations are not permitted. CXL region driver returns -EPERM for
> region destroy operations.

The above intro is too narrow for why region may be locked. See v1
comments. Let's keep it similar to the sysfs 'Description:' field,
like this:

The CXL driver has the capability to lock a region based on a BIOS or
platform dependent configuration. Region destroy operations are not
permitted on locked regions and the CXL region driver returns -EPERM
for region destroy operations.

Otherwise, LGTM 
Reviewed-by: Alison Schofield <alison.schofield@xxxxxxxxx>


> 
> Although the locked status of the corresponding root decoder implies the
> region is also locked, exposing the region lock status directly to
> userspace improves usability for users who may not be aware of this
> relationship.
> 
> Signed-off-by: Li Ming <ming.li@xxxxxxxxxxxx>
> Reviewed-by: Dave Jiang <dave.jiang@xxxxxxxxx>
> Reviewed-by: Alejandro Lucero <alucerop@xxxxxxx>
> ---
> v2:
> * Add more info to the interface description. (Alison)
> ---
>  Documentation/ABI/testing/sysfs-bus-cxl | 13 +++++++++++++
>  drivers/cxl/core/region.c               | 17 +++++++++++++++++
>  2 files changed, 30 insertions(+)
> 
> diff --git a/Documentation/ABI/testing/sysfs-bus-cxl b/Documentation/ABI/testing/sysfs-bus-cxl
> index c80a1b5a03db..16a9b3d2e2c0 100644
> --- a/Documentation/ABI/testing/sysfs-bus-cxl
> +++ b/Documentation/ABI/testing/sysfs-bus-cxl
> @@ -508,6 +508,19 @@ Description:
>  		(RO) The size of extended linear cache, if there is an extended
>  		linear cache. Otherwise the attribute will not be visible.
>  
> +
> +What:		/sys/bus/cxl/devices/regionZ/locked
> +Date:		Mar, 2026
> +KernelVersion:	v7.1
> +Contact:	linux-cxl@xxxxxxxxxxxxxxx
> +Description:
> +		(RO) The CXL driver has the capability to lock a region based on
> +		a BIOS or platform dependent configuration. Regions created as
> +		locked are never permitted to be destroyed. Resets to participating
> +		decoders will not result in a region destroy and will not free the
> +		decoder resources.
> +
> +
>  What:		/sys/bus/cxl/devices/regionZ/mode
>  Date:		January, 2023
>  KernelVersion:	v6.3
> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> index 42874948b589..95d81816008e 100644
> --- a/drivers/cxl/core/region.c
> +++ b/drivers/cxl/core/region.c
> @@ -767,6 +767,22 @@ static ssize_t extended_linear_cache_size_show(struct device *dev,
>  }
>  static DEVICE_ATTR_RO(extended_linear_cache_size);
>  
> +static ssize_t locked_show(struct device *dev,
> +			   struct device_attribute *attr,
> +			   char *buf)
> +{
> +	struct cxl_region *cxlr = to_cxl_region(dev);
> +	int rc;
> +
> +	ACQUIRE(rwsem_read_intr, rwsem)(&cxl_rwsem.region);
> +	if ((rc = ACQUIRE_ERR(rwsem_read_intr, &rwsem)))
> +		return rc;
> +
> +	rc = test_bit(CXL_REGION_F_LOCK, &cxlr->flags);
> +	return sysfs_emit(buf, "%d\n", rc);
> +}
> +static DEVICE_ATTR_RO(locked);
> +
>  static struct attribute *cxl_region_attrs[] = {
>  	&dev_attr_uuid.attr,
>  	&dev_attr_commit.attr,
> @@ -776,6 +792,7 @@ static struct attribute *cxl_region_attrs[] = {
>  	&dev_attr_size.attr,
>  	&dev_attr_mode.attr,
>  	&dev_attr_extended_linear_cache_size.attr,
> +	&dev_attr_locked.attr,
>  	NULL,
>  };
>  
> -- 
> 2.43.0
>