diff mbox series

[v4,22/28] cxl/region/extent: Expose region extent information in sysfs

Message ID 20241007-dcd-type2-upstream-v4-22-c261ee6eeded@intel.com (mailing list archive)
State Superseded, archived
Delegated to: Ira Weiny
Headers show
Series DCD: Add support for Dynamic Capacity Devices (DCD) | expand

Commit Message

Ira Weiny Oct. 7, 2024, 11:16 p.m. UTC 
From: Navneet Singh <navneet.singh@intel.com>

Extent information can be helpful to the user to coordinate memory usage
with the external orchestrator and FM.

Expose the details of region extents by creating the following
sysfs entries.

        /sys/bus/cxl/devices/dax_regionX/extentX.Y
        /sys/bus/cxl/devices/dax_regionX/extentX.Y/offset
        /sys/bus/cxl/devices/dax_regionX/extentX.Y/length
        /sys/bus/cxl/devices/dax_regionX/extentX.Y/tag

Signed-off-by: Navneet Singh <navneet.singh@intel.com>
Co-developed-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Ira Weiny <ira.weiny@intel.com>

---
Changes:
[djiang: Split sysfs docs up]
[iweiny: Adjust sysfs docs dates]
---
 Documentation/ABI/testing/sysfs-bus-cxl | 32 ++++++++++++++++++
 drivers/cxl/core/extent.c               | 58 +++++++++++++++++++++++++++++++++
 2 files changed, 90 insertions(+)

Comments

Jonathan Cameron Oct. 10, 2024, 3:01 p.m. UTC | #1 
On Mon, 07 Oct 2024 18:16:28 -0500
ira.weiny@intel.com wrote:

> From: Navneet Singh <navneet.singh@intel.com>
> 
> Extent information can be helpful to the user to coordinate memory usage
> with the external orchestrator and FM.
> 
> Expose the details of region extents by creating the following
> sysfs entries.
> 
>         /sys/bus/cxl/devices/dax_regionX/extentX.Y
>         /sys/bus/cxl/devices/dax_regionX/extentX.Y/offset
>         /sys/bus/cxl/devices/dax_regionX/extentX.Y/length
>         /sys/bus/cxl/devices/dax_regionX/extentX.Y/tag
> 
> Signed-off-by: Navneet Singh <navneet.singh@intel.com>
> Co-developed-by: Ira Weiny <ira.weiny@intel.com>
> Signed-off-by: Ira Weiny <ira.weiny@intel.com>
> 
Trivial comments inline.

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

> ---
> Changes:
> [djiang: Split sysfs docs up]
> [iweiny: Adjust sysfs docs dates]
> ---
>  Documentation/ABI/testing/sysfs-bus-cxl | 32 ++++++++++++++++++
>  drivers/cxl/core/extent.c               | 58 +++++++++++++++++++++++++++++++++
>  2 files changed, 90 insertions(+)
> 
> diff --git a/Documentation/ABI/testing/sysfs-bus-cxl b/Documentation/ABI/testing/sysfs-bus-cxl
> index b63ab622515f..64918180a3c9 100644
> --- a/Documentation/ABI/testing/sysfs-bus-cxl
> +++ b/Documentation/ABI/testing/sysfs-bus-cxl
> @@ -632,3 +632,35 @@ Description:
>  		See Documentation/ABI/stable/sysfs-devices-node. access0 provides
>  		the number to the closest initiator and access1 provides the
>  		number to the closest CPU.
> +
> +What:		/sys/bus/cxl/devices/dax_regionX/extentX.Y/offset
> +Date:		December, 2024
> +KernelVersion:	v6.13
> +Contact:	linux-cxl@vger.kernel.org
> +Description:
> +		(RO) [For Dynamic Capacity regions only] Users can use the
> +		extent information to create DAX devices on specific extents.
> +		This is done by creating and destroying DAX devices in specific
> +		sequences and looking at the mappings created. 

Similar to earlier patch, maybe put this doc for the directory, then
have much less duplication?


> Extent offset
> +		within the region.
> +
> +What:		/sys/bus/cxl/devices/dax_regionX/extentX.Y/length
> +Date:		December, 2024
> +KernelVersion:	v6.13
> +Contact:	linux-cxl@vger.kernel.org
> +Description:
> +		(RO) [For Dynamic Capacity regions only] Users can use the
> +		extent information to create DAX devices on specific extents.
> +		This is done by creating and destroying DAX devices in specific
> +		sequences and looking at the mappings created.  Extent length
> +		within the region.
> +
> +What:		/sys/bus/cxl/devices/dax_regionX/extentX.Y/tag
> +Date:		December, 2024
> +KernelVersion:	v6.13
> +Contact:	linux-cxl@vger.kernel.org
> +Description:
> +		(RO) [For Dynamic Capacity regions only] Users can use the
> +		extent information to create DAX devices on specific extents.
> +		This is done by creating and destroying DAX devices in specific
> +		sequences and looking at the mappings created.  Extent tag.

Maybe say we are treating it as a UUID?

> diff --git a/drivers/cxl/core/extent.c b/drivers/cxl/core/extent.c
> index 69a7614ba6a9..a1eb6e8e4f1a 100644
> --- a/drivers/cxl/core/extent.c
> +++ b/drivers/cxl/core/extent.c
> @@ -6,6 +6,63 @@

> +static struct attribute *region_extent_attrs[] = {
> +	&dev_attr_offset.attr,
> +	&dev_attr_length.attr,
> +	&dev_attr_tag.attr,
> +	NULL,
No need for trailing comma (one of my 'favourite' review comments :)

> +};
Fan Ni Oct. 14, 2024, 4:08 p.m. UTC | #2 
On Mon, Oct 07, 2024 at 06:16:28PM -0500, ira.weiny@intel.com wrote:
> From: Navneet Singh <navneet.singh@intel.com>
> 
> Extent information can be helpful to the user to coordinate memory usage
> with the external orchestrator and FM.
> 
> Expose the details of region extents by creating the following
> sysfs entries.
> 
>         /sys/bus/cxl/devices/dax_regionX/extentX.Y
>         /sys/bus/cxl/devices/dax_regionX/extentX.Y/offset
>         /sys/bus/cxl/devices/dax_regionX/extentX.Y/length
>         /sys/bus/cxl/devices/dax_regionX/extentX.Y/tag
> 
> Signed-off-by: Navneet Singh <navneet.singh@intel.com>
> Co-developed-by: Ira Weiny <ira.weiny@intel.com>
> Signed-off-by: Ira Weiny <ira.weiny@intel.com>
> 

Reviewed-by: Fan Ni <fan.ni@samsung.com>
Tested-by: Fan Ni <fan.ni@samsung.com>

> ---
> Changes:
> [djiang: Split sysfs docs up]
> [iweiny: Adjust sysfs docs dates]
> ---
>  Documentation/ABI/testing/sysfs-bus-cxl | 32 ++++++++++++++++++
>  drivers/cxl/core/extent.c               | 58 +++++++++++++++++++++++++++++++++
>  2 files changed, 90 insertions(+)
> 
> diff --git a/Documentation/ABI/testing/sysfs-bus-cxl b/Documentation/ABI/testing/sysfs-bus-cxl
> index b63ab622515f..64918180a3c9 100644
> --- a/Documentation/ABI/testing/sysfs-bus-cxl
> +++ b/Documentation/ABI/testing/sysfs-bus-cxl
> @@ -632,3 +632,35 @@ Description:
>  		See Documentation/ABI/stable/sysfs-devices-node. access0 provides
>  		the number to the closest initiator and access1 provides the
>  		number to the closest CPU.
> +
> +What:		/sys/bus/cxl/devices/dax_regionX/extentX.Y/offset
> +Date:		December, 2024
> +KernelVersion:	v6.13
> +Contact:	linux-cxl@vger.kernel.org
> +Description:
> +		(RO) [For Dynamic Capacity regions only] Users can use the
> +		extent information to create DAX devices on specific extents.
> +		This is done by creating and destroying DAX devices in specific
> +		sequences and looking at the mappings created.  Extent offset
> +		within the region.
> +
> +What:		/sys/bus/cxl/devices/dax_regionX/extentX.Y/length
> +Date:		December, 2024
> +KernelVersion:	v6.13
> +Contact:	linux-cxl@vger.kernel.org
> +Description:
> +		(RO) [For Dynamic Capacity regions only] Users can use the
> +		extent information to create DAX devices on specific extents.
> +		This is done by creating and destroying DAX devices in specific
> +		sequences and looking at the mappings created.  Extent length
> +		within the region.
> +
> +What:		/sys/bus/cxl/devices/dax_regionX/extentX.Y/tag
> +Date:		December, 2024
> +KernelVersion:	v6.13
> +Contact:	linux-cxl@vger.kernel.org
> +Description:
> +		(RO) [For Dynamic Capacity regions only] Users can use the
> +		extent information to create DAX devices on specific extents.
> +		This is done by creating and destroying DAX devices in specific
> +		sequences and looking at the mappings created.  Extent tag.
> diff --git a/drivers/cxl/core/extent.c b/drivers/cxl/core/extent.c
> index 69a7614ba6a9..a1eb6e8e4f1a 100644
> --- a/drivers/cxl/core/extent.c
> +++ b/drivers/cxl/core/extent.c
> @@ -6,6 +6,63 @@
>  
>  #include "core.h"
>  
> +static ssize_t offset_show(struct device *dev, struct device_attribute *attr,
> +			   char *buf)
> +{
> +	struct region_extent *region_extent = to_region_extent(dev);
> +
> +	return sysfs_emit(buf, "%#llx\n", region_extent->hpa_range.start);
> +}
> +static DEVICE_ATTR_RO(offset);
> +
> +static ssize_t length_show(struct device *dev, struct device_attribute *attr,
> +			   char *buf)
> +{
> +	struct region_extent *region_extent = to_region_extent(dev);
> +	u64 length = range_len(&region_extent->hpa_range);
> +
> +	return sysfs_emit(buf, "%#llx\n", length);
> +}
> +static DEVICE_ATTR_RO(length);
> +
> +static ssize_t tag_show(struct device *dev, struct device_attribute *attr,
> +			char *buf)
> +{
> +	struct region_extent *region_extent = to_region_extent(dev);
> +
> +	return sysfs_emit(buf, "%pUb\n", &region_extent->tag);
> +}
> +static DEVICE_ATTR_RO(tag);
> +
> +static struct attribute *region_extent_attrs[] = {
> +	&dev_attr_offset.attr,
> +	&dev_attr_length.attr,
> +	&dev_attr_tag.attr,
> +	NULL,
> +};
> +
> +static uuid_t empty_tag = { 0 };
> +
> +static umode_t region_extent_visible(struct kobject *kobj,
> +				     struct attribute *a, int n)
> +{
> +	struct device *dev = kobj_to_dev(kobj);
> +	struct region_extent *region_extent = to_region_extent(dev);
> +
> +	if (a == &dev_attr_tag.attr &&
> +	    uuid_equal(&region_extent->tag, &empty_tag))
> +		return 0;
> +
> +	return a->mode;
> +}
> +
> +static const struct attribute_group region_extent_attribute_group = {
> +	.attrs = region_extent_attrs,
> +	.is_visible = region_extent_visible,
> +};
> +
> +__ATTRIBUTE_GROUPS(region_extent_attribute);
> +
>  static void cxled_release_extent(struct cxl_endpoint_decoder *cxled,
>  				 struct cxled_extent *ed_extent)
>  {
> @@ -44,6 +101,7 @@ static void region_extent_release(struct device *dev)
>  static const struct device_type region_extent_type = {
>  	.name = "extent",
>  	.release = region_extent_release,
> +	.groups = region_extent_attribute_groups,
>  };
>  
>  bool is_region_extent(struct device *dev)
> 
> -- 
> 2.46.0
>
Ira Weiny Oct. 18, 2024, 6:26 p.m. UTC | #3 
Jonathan Cameron wrote:
> On Mon, 07 Oct 2024 18:16:28 -0500
> ira.weiny@intel.com wrote:
> 
> > From: Navneet Singh <navneet.singh@intel.com>
> > 
> > Extent information can be helpful to the user to coordinate memory usage
> > with the external orchestrator and FM.
> > 
> > Expose the details of region extents by creating the following
> > sysfs entries.
> > 
> >         /sys/bus/cxl/devices/dax_regionX/extentX.Y
> >         /sys/bus/cxl/devices/dax_regionX/extentX.Y/offset
> >         /sys/bus/cxl/devices/dax_regionX/extentX.Y/length
> >         /sys/bus/cxl/devices/dax_regionX/extentX.Y/tag
> > 
> > Signed-off-by: Navneet Singh <navneet.singh@intel.com>
> > Co-developed-by: Ira Weiny <ira.weiny@intel.com>
> > Signed-off-by: Ira Weiny <ira.weiny@intel.com>
> > 
> Trivial comments inline.
> 
> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Thanks!

> 
> > ---
> > Changes:
> > [djiang: Split sysfs docs up]
> > [iweiny: Adjust sysfs docs dates]
> > ---
> >  Documentation/ABI/testing/sysfs-bus-cxl | 32 ++++++++++++++++++
> >  drivers/cxl/core/extent.c               | 58 +++++++++++++++++++++++++++++++++
> >  2 files changed, 90 insertions(+)
> > 
> > diff --git a/Documentation/ABI/testing/sysfs-bus-cxl b/Documentation/ABI/testing/sysfs-bus-cxl
> > index b63ab622515f..64918180a3c9 100644
> > --- a/Documentation/ABI/testing/sysfs-bus-cxl
> > +++ b/Documentation/ABI/testing/sysfs-bus-cxl
> > @@ -632,3 +632,35 @@ Description:
> >  		See Documentation/ABI/stable/sysfs-devices-node. access0 provides
> >  		the number to the closest initiator and access1 provides the
> >  		number to the closest CPU.
> > +
> > +What:		/sys/bus/cxl/devices/dax_regionX/extentX.Y/offset
> > +Date:		December, 2024
> > +KernelVersion:	v6.13
> > +Contact:	linux-cxl@vger.kernel.org
> > +Description:
> > +		(RO) [For Dynamic Capacity regions only] Users can use the
> > +		extent information to create DAX devices on specific extents.
> > +		This is done by creating and destroying DAX devices in specific
> > +		sequences and looking at the mappings created. 
> 
> Similar to earlier patch, maybe put this doc for the directory, then
> have much less duplication?
> 

But none of the other directories are done this way so I'm inclined to keep it.

> 
> > Extent offset
> > +		within the region.
> > +
> > +What:		/sys/bus/cxl/devices/dax_regionX/extentX.Y/length
> > +Date:		December, 2024
> > +KernelVersion:	v6.13
> > +Contact:	linux-cxl@vger.kernel.org
> > +Description:
> > +		(RO) [For Dynamic Capacity regions only] Users can use the
> > +		extent information to create DAX devices on specific extents.
> > +		This is done by creating and destroying DAX devices in specific
> > +		sequences and looking at the mappings created.  Extent length
> > +		within the region.
> > +
> > +What:		/sys/bus/cxl/devices/dax_regionX/extentX.Y/tag
> > +Date:		December, 2024
> > +KernelVersion:	v6.13
> > +Contact:	linux-cxl@vger.kernel.org
> > +Description:
> > +		(RO) [For Dynamic Capacity regions only] Users can use the
> > +		extent information to create DAX devices on specific extents.
> > +		This is done by creating and destroying DAX devices in specific
> > +		sequences and looking at the mappings created.  Extent tag.
> 
> Maybe say we are treating it as a UUID?

ok...  How about?

<quote>
...  looking at the mappings created.  UUID extent tag.
</quote>

> > diff --git a/drivers/cxl/core/extent.c b/drivers/cxl/core/extent.c
> > index 69a7614ba6a9..a1eb6e8e4f1a 100644
> > --- a/drivers/cxl/core/extent.c
> > +++ b/drivers/cxl/core/extent.c
> > @@ -6,6 +6,63 @@
> 
> > +static struct attribute *region_extent_attrs[] = {
> > +	&dev_attr_offset.attr,
> > +	&dev_attr_length.attr,
> > +	&dev_attr_tag.attr,
> > +	NULL,
> No need for trailing comma (one of my 'favourite' review comments :)

I'm noticing...  :-D

Ira
Jonathan Cameron Oct. 21, 2024, 9:37 a.m. UTC | #4 
On Fri, 18 Oct 2024 13:26:14 -0500
Ira Weiny <ira.weiny@intel.com> wrote:

> Jonathan Cameron wrote:
> > On Mon, 07 Oct 2024 18:16:28 -0500
> > ira.weiny@intel.com wrote:
> >   
> > > From: Navneet Singh <navneet.singh@intel.com>
> > > 
> > > Extent information can be helpful to the user to coordinate memory usage
> > > with the external orchestrator and FM.
> > > 
> > > Expose the details of region extents by creating the following
> > > sysfs entries.
> > > 
> > >         /sys/bus/cxl/devices/dax_regionX/extentX.Y
> > >         /sys/bus/cxl/devices/dax_regionX/extentX.Y/offset
> > >         /sys/bus/cxl/devices/dax_regionX/extentX.Y/length
> > >         /sys/bus/cxl/devices/dax_regionX/extentX.Y/tag
> > > 
> > > Signed-off-by: Navneet Singh <navneet.singh@intel.com>
> > > Co-developed-by: Ira Weiny <ira.weiny@intel.com>
> > > Signed-off-by: Ira Weiny <ira.weiny@intel.com>
> > >   
> > Trivial comments inline.
> > 
> > Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>  
> 
> Thanks!
> 
> >   
> > > ---
> > > Changes:
> > > [djiang: Split sysfs docs up]
> > > [iweiny: Adjust sysfs docs dates]
> > > ---
> > >  Documentation/ABI/testing/sysfs-bus-cxl | 32 ++++++++++++++++++
> > >  drivers/cxl/core/extent.c               | 58 +++++++++++++++++++++++++++++++++
> > >  2 files changed, 90 insertions(+)
> > > 
> > > diff --git a/Documentation/ABI/testing/sysfs-bus-cxl b/Documentation/ABI/testing/sysfs-bus-cxl
> > > index b63ab622515f..64918180a3c9 100644
> > > --- a/Documentation/ABI/testing/sysfs-bus-cxl
> > > +++ b/Documentation/ABI/testing/sysfs-bus-cxl
> > > @@ -632,3 +632,35 @@ Description:
> > >  		See Documentation/ABI/stable/sysfs-devices-node. access0 provides
> > >  		the number to the closest initiator and access1 provides the
> > >  		number to the closest CPU.
> > > +
> > > +What:		/sys/bus/cxl/devices/dax_regionX/extentX.Y/offset
> > > +Date:		December, 2024
> > > +KernelVersion:	v6.13
> > > +Contact:	linux-cxl@vger.kernel.org
> > > +Description:
> > > +		(RO) [For Dynamic Capacity regions only] Users can use the
> > > +		extent information to create DAX devices on specific extents.
> > > +		This is done by creating and destroying DAX devices in specific
> > > +		sequences and looking at the mappings created.   
> > 
> > Similar to earlier patch, maybe put this doc for the directory, then
> > have much less duplication?
> >   
> 
> But none of the other directories are done this way so I'm inclined to keep it.

Fair enough. Maybe a topic for a future cleanup to reduce duplication.

> 
> >   
> > > Extent offset
> > > +		within the region.
> > > +
> > > +What:		/sys/bus/cxl/devices/dax_regionX/extentX.Y/length
> > > +Date:		December, 2024
> > > +KernelVersion:	v6.13
> > > +Contact:	linux-cxl@vger.kernel.org
> > > +Description:
> > > +		(RO) [For Dynamic Capacity regions only] Users can use the
> > > +		extent information to create DAX devices on specific extents.
> > > +		This is done by creating and destroying DAX devices in specific
> > > +		sequences and looking at the mappings created.  Extent length
> > > +		within the region.
> > > +
> > > +What:		/sys/bus/cxl/devices/dax_regionX/extentX.Y/tag
> > > +Date:		December, 2024
> > > +KernelVersion:	v6.13
> > > +Contact:	linux-cxl@vger.kernel.org
> > > +Description:
> > > +		(RO) [For Dynamic Capacity regions only] Users can use the
> > > +		extent information to create DAX devices on specific extents.
> > > +		This is done by creating and destroying DAX devices in specific
> > > +		sequences and looking at the mappings created.  Extent tag.  
> > 
> > Maybe say we are treating it as a UUID?  
> 
> ok...  How about?
> 
> <quote>
> ...  looking at the mappings created.  UUID extent tag.
That's fine.

> </quote>
> 
> > > diff --git a/drivers/cxl/core/extent.c b/drivers/cxl/core/extent.c
> > > index 69a7614ba6a9..a1eb6e8e4f1a 100644
> > > --- a/drivers/cxl/core/extent.c
> > > +++ b/drivers/cxl/core/extent.c
> > > @@ -6,6 +6,63 @@  
> >   
> > > +static struct attribute *region_extent_attrs[] = {
> > > +	&dev_attr_offset.attr,
> > > +	&dev_attr_length.attr,
> > > +	&dev_attr_tag.attr,
> > > +	NULL,  
> > No need for trailing comma (one of my 'favourite' review comments :)  
> 
> I'm noticing...  :-D
Maybe I'll one day add to checkpatch.  If it weren't written in perl
I'd do it now ;)

Jonathan

> 
> Ira
>
diff mbox series

Patch

diff --git a/Documentation/ABI/testing/sysfs-bus-cxl b/Documentation/ABI/testing/sysfs-bus-cxl
index b63ab622515f..64918180a3c9 100644
--- a/Documentation/ABI/testing/sysfs-bus-cxl
+++ b/Documentation/ABI/testing/sysfs-bus-cxl
@@ -632,3 +632,35 @@  Description:
 		See Documentation/ABI/stable/sysfs-devices-node. access0 provides
 		the number to the closest initiator and access1 provides the
 		number to the closest CPU.
+
+What:		/sys/bus/cxl/devices/dax_regionX/extentX.Y/offset
+Date:		December, 2024
+KernelVersion:	v6.13
+Contact:	linux-cxl@vger.kernel.org
+Description:
+		(RO) [For Dynamic Capacity regions only] Users can use the
+		extent information to create DAX devices on specific extents.
+		This is done by creating and destroying DAX devices in specific
+		sequences and looking at the mappings created.  Extent offset
+		within the region.
+
+What:		/sys/bus/cxl/devices/dax_regionX/extentX.Y/length
+Date:		December, 2024
+KernelVersion:	v6.13
+Contact:	linux-cxl@vger.kernel.org
+Description:
+		(RO) [For Dynamic Capacity regions only] Users can use the
+		extent information to create DAX devices on specific extents.
+		This is done by creating and destroying DAX devices in specific
+		sequences and looking at the mappings created.  Extent length
+		within the region.
+
+What:		/sys/bus/cxl/devices/dax_regionX/extentX.Y/tag
+Date:		December, 2024
+KernelVersion:	v6.13
+Contact:	linux-cxl@vger.kernel.org
+Description:
+		(RO) [For Dynamic Capacity regions only] Users can use the
+		extent information to create DAX devices on specific extents.
+		This is done by creating and destroying DAX devices in specific
+		sequences and looking at the mappings created.  Extent tag.
diff --git a/drivers/cxl/core/extent.c b/drivers/cxl/core/extent.c
index 69a7614ba6a9..a1eb6e8e4f1a 100644
--- a/drivers/cxl/core/extent.c
+++ b/drivers/cxl/core/extent.c
@@ -6,6 +6,63 @@ 
 
 #include "core.h"
 
+static ssize_t offset_show(struct device *dev, struct device_attribute *attr,
+			   char *buf)
+{
+	struct region_extent *region_extent = to_region_extent(dev);
+
+	return sysfs_emit(buf, "%#llx\n", region_extent->hpa_range.start);
+}
+static DEVICE_ATTR_RO(offset);
+
+static ssize_t length_show(struct device *dev, struct device_attribute *attr,
+			   char *buf)
+{
+	struct region_extent *region_extent = to_region_extent(dev);
+	u64 length = range_len(&region_extent->hpa_range);
+
+	return sysfs_emit(buf, "%#llx\n", length);
+}
+static DEVICE_ATTR_RO(length);
+
+static ssize_t tag_show(struct device *dev, struct device_attribute *attr,
+			char *buf)
+{
+	struct region_extent *region_extent = to_region_extent(dev);
+
+	return sysfs_emit(buf, "%pUb\n", &region_extent->tag);
+}
+static DEVICE_ATTR_RO(tag);
+
+static struct attribute *region_extent_attrs[] = {
+	&dev_attr_offset.attr,
+	&dev_attr_length.attr,
+	&dev_attr_tag.attr,
+	NULL,
+};
+
+static uuid_t empty_tag = { 0 };
+
+static umode_t region_extent_visible(struct kobject *kobj,
+				     struct attribute *a, int n)
+{
+	struct device *dev = kobj_to_dev(kobj);
+	struct region_extent *region_extent = to_region_extent(dev);
+
+	if (a == &dev_attr_tag.attr &&
+	    uuid_equal(&region_extent->tag, &empty_tag))
+		return 0;
+
+	return a->mode;
+}
+
+static const struct attribute_group region_extent_attribute_group = {
+	.attrs = region_extent_attrs,
+	.is_visible = region_extent_visible,
+};
+
+__ATTRIBUTE_GROUPS(region_extent_attribute);
+
 static void cxled_release_extent(struct cxl_endpoint_decoder *cxled,
 				 struct cxled_extent *ed_extent)
 {
@@ -44,6 +101,7 @@  static void region_extent_release(struct device *dev)
 static const struct device_type region_extent_type = {
 	.name = "extent",
 	.release = region_extent_release,
+	.groups = region_extent_attribute_groups,
 };
 
 bool is_region_extent(struct device *dev)