cxl/region: Add a region sysfs interface for region lock status

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

Posted by Li Ming 3 days, 18 hours ago

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.

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@zohomail.com>
---
 Documentation/ABI/testing/sysfs-bus-cxl | 10 ++++++++++
 drivers/cxl/core/region.c               | 17 +++++++++++++++++
 2 files changed, 27 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-bus-cxl b/Documentation/ABI/testing/sysfs-bus-cxl
index c80a1b5a03db..50bf7334465b 100644
--- a/Documentation/ABI/testing/sysfs-bus-cxl
+++ b/Documentation/ABI/testing/sysfs-bus-cxl
@@ -508,6 +508,16 @@ 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@vger.kernel.org
+Description:
+		(RO) The lock status of the region, region destroy operations
+		are not permitted if the region is locked.
+
+
 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,
 };
 

---
base-commit: c369299895a591d96745d6492d4888259b004a9e
change-id: 20260329-expose_region_locked_status-b05c4b8f97d6

Best regards,
-- 
Li Ming <ming.li@zohomail.com>

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

Posted by Alison Schofield 1 day, 9 hours ago

On Sun, Mar 29, 2026 at 10:44:17PM +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.
> 

There is at least 3 paths to a locked region:

1) the FIXED root decoder attribute (above)

2) CXL_HDM_DECODER0_CTRL_LOCK
   Both 1) and 2) well described in:
   2230c4bdc412 ("cxl: Add handling of locked CXL decoder")

3) AMD Zen5 region creation always locks the region, regardless of the
   FIXED attribute or decoder ctrl bit.


I like the added info provided by this patch. Please consider expanding
the sysfs 'Decription:' field. If user reads the decoder lock sysfs
description they may think they can reset their way out of a region lock
situation, and I don't think they can.

more...

> 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@zohomail.com>
> ---
>  Documentation/ABI/testing/sysfs-bus-cxl | 10 ++++++++++
>  drivers/cxl/core/region.c               | 17 +++++++++++++++++
>  2 files changed, 27 insertions(+)
> 
> diff --git a/Documentation/ABI/testing/sysfs-bus-cxl b/Documentation/ABI/testing/sysfs-bus-cxl
> index c80a1b5a03db..50bf7334465b 100644
> --- a/Documentation/ABI/testing/sysfs-bus-cxl
> +++ b/Documentation/ABI/testing/sysfs-bus-cxl
> @@ -508,6 +508,16 @@ 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@vger.kernel.org
> +Description:
> +		(RO) The lock status of the region, region destroy operations
> +		are not permitted if the region is locked.

Maybe similar to the sys/bus/cxl/devices/decoderX.Y/locked, say:

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.

Maybe the last sentence is too much.


> +
> +
>  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,
>  };
>  
> 
> ---
> base-commit: c369299895a591d96745d6492d4888259b004a9e
> change-id: 20260329-expose_region_locked_status-b05c4b8f97d6
> 
> Best regards,
> -- 
> Li Ming <ming.li@zohomail.com>
>

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

Posted by Alejandro Lucero Palau 2 days, 3 hours ago

On 3/29/26 15:44, 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.
>
> 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@zohomail.com>
> ---
>   Documentation/ABI/testing/sysfs-bus-cxl | 10 ++++++++++
>   drivers/cxl/core/region.c               | 17 +++++++++++++++++
>   2 files changed, 27 insertions(+)
>
> diff --git a/Documentation/ABI/testing/sysfs-bus-cxl b/Documentation/ABI/testing/sysfs-bus-cxl
> index c80a1b5a03db..50bf7334465b 100644
> --- a/Documentation/ABI/testing/sysfs-bus-cxl
> +++ b/Documentation/ABI/testing/sysfs-bus-cxl
> @@ -508,6 +508,16 @@ 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@vger.kernel.org
> +Description:
> +		(RO) The lock status of the region, region destroy operations
> +		are not permitted if the region is locked.
> +
> +
>   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,
>   };
>   
>
> ---
> base-commit: c369299895a591d96745d6492d4888259b004a9e
> change-id: 20260329-expose_region_locked_status-b05c4b8f97d6
>
> Best regards,


Reviewed-by: Alejandro Lucero <alucerop@amd.com>

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

Posted by Dave Jiang 2 days, 11 hours ago


On 3/29/26 7:44 AM, 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.
> 
> 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@zohomail.com>

Reviewed-by: Dave Jiang <dave.jiang@intel.com>


> ---
>  Documentation/ABI/testing/sysfs-bus-cxl | 10 ++++++++++
>  drivers/cxl/core/region.c               | 17 +++++++++++++++++
>  2 files changed, 27 insertions(+)
> 
> diff --git a/Documentation/ABI/testing/sysfs-bus-cxl b/Documentation/ABI/testing/sysfs-bus-cxl
> index c80a1b5a03db..50bf7334465b 100644
> --- a/Documentation/ABI/testing/sysfs-bus-cxl
> +++ b/Documentation/ABI/testing/sysfs-bus-cxl
> @@ -508,6 +508,16 @@ 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@vger.kernel.org
> +Description:
> +		(RO) The lock status of the region, region destroy operations
> +		are not permitted if the region is locked.
> +
> +
>  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,
>  };
>  
> 
> ---
> base-commit: c369299895a591d96745d6492d4888259b004a9e
> change-id: 20260329-expose_region_locked_status-b05c4b8f97d6
> 
> Best regards,