* Re: [PATCH] cxl/region: Add a region sysfs interface for region lock status
2026-03-29 14:44 [PATCH] cxl/region: Add a region sysfs interface for region lock status Li Ming
@ 2026-03-30 21:57 ` Dave Jiang
2026-03-31 5:48 ` Alejandro Lucero Palau
2026-03-31 23:57 ` Alison Schofield
2 siblings, 0 replies; 4+ messages in thread
From: Dave Jiang @ 2026-03-30 21:57 UTC (permalink / raw)
To: Li Ming, Davidlohr Bueso, Jonathan Cameron, Alison Schofield,
Vishal Verma, Ira Weiny, Dan Williams
Cc: linux-kernel, linux-cxl
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,
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH] cxl/region: Add a region sysfs interface for region lock status
2026-03-29 14:44 [PATCH] cxl/region: Add a region sysfs interface for region lock status Li Ming
2026-03-30 21:57 ` Dave Jiang
@ 2026-03-31 5:48 ` Alejandro Lucero Palau
2026-03-31 23:57 ` Alison Schofield
2 siblings, 0 replies; 4+ messages in thread
From: Alejandro Lucero Palau @ 2026-03-31 5:48 UTC (permalink / raw)
To: Li Ming, Davidlohr Bueso, Jonathan Cameron, Dave Jiang,
Alison Schofield, Vishal Verma, Ira Weiny, Dan Williams
Cc: linux-kernel, linux-cxl
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>
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH] cxl/region: Add a region sysfs interface for region lock status
2026-03-29 14:44 [PATCH] cxl/region: Add a region sysfs interface for region lock status Li Ming
2026-03-30 21:57 ` Dave Jiang
2026-03-31 5:48 ` Alejandro Lucero Palau
@ 2026-03-31 23:57 ` Alison Schofield
2 siblings, 0 replies; 4+ messages in thread
From: Alison Schofield @ 2026-03-31 23:57 UTC (permalink / raw)
To: Li Ming
Cc: Davidlohr Bueso, Jonathan Cameron, Dave Jiang, Vishal Verma,
Ira Weiny, Dan Williams, linux-kernel, linux-cxl
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>
>
^ permalink raw reply [flat|nested] 4+ messages in thread