Re: [PATCH v4 06/24] coco/tdx-host: Expose P-SEAMLDR information via sysfs

[Binbin Wu]

On 2/12/2026 10:35 PM, Chao Gao wrote:
> TDX Module updates require userspace to select the appropriate module
> to load. Expose necessary information to facilitate this decision. Two
> values are needed:
> 
> - P-SEAMLDR version: for compatibility checks between TDX Module and
> 		     P-SEAMLDR
> - num_remaining_updates: indicates how many updates can be performed
> 
> Expose them as tdx-host device attributes.
> 
> Signed-off-by: Chao Gao <chao.gao@xxxxxxxxx>
> Reviewed-by: Tony Lindgren <tony.lindgren@xxxxxxxxxxxxxxx>
> Tested-by: Farrah Chen <farrah.chen@xxxxxxxxx>


Reviewed-by: Binbin Wu <binbin.wu@xxxxxxxxxxxxxxx>

Some nits below.

> ---
> v4:
>  - Make seamldr attribute permission "0400" [Dave]
>  - Don't include implementation details in OS ABI docs [Dave]
>  - Tag tdx_host_group as static [Kai]
> 
> v3:
>  - use #ifdef rather than .is_visible() to control P-SEAMLDR sysfs
>    visibility [Yilun]
> ---
>  .../ABI/testing/sysfs-devices-faux-tdx-host   | 23 +++++++
>  drivers/virt/coco/tdx-host/tdx-host.c         | 63 ++++++++++++++++++-
>  2 files changed, 85 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/ABI/testing/sysfs-devices-faux-tdx-host b/Documentation/ABI/testing/sysfs-devices-faux-tdx-host
> index 901abbae2e61..88a9c0b2bdfe 100644
> --- a/Documentation/ABI/testing/sysfs-devices-faux-tdx-host
> +++ b/Documentation/ABI/testing/sysfs-devices-faux-tdx-host
> @@ -4,3 +4,26 @@ Description:	(RO) Report the version of the loaded TDX Module. The TDX Module
>  		version is formatted as x.y.z, where "x" is the major version,
>  		"y" is the minor version and "z" is the update version. Versions
>  		are used for bug reporting, TDX Module updates and etc.
> +
> +What:		/sys/devices/faux/tdx_host/seamldr/version
> +Contact:	linux-coco@xxxxxxxxxxxxxxx
> +Description:	(RO) Report the version of the loaded SEAM loader. The SEAM
> +		loader version is formatted as x.y.z, where "x" is the major
> +		version, "y" is the minor version and "z" is the update version.
> +		Versions are used for bug reporting and compatibility checks.
> +
> +What:		/sys/devices/faux/tdx_host/seamldr/num_remaining_updates
> +Contact:	linux-coco@xxxxxxxxxxxxxxx
> +Description:	(RO) Report the number of remaining updates. TDX maintains a
> +		log about each TDX Module which has been loaded. This log has
                                            ^
                                          that
> +		a finite size which limits the number of TDX Module updates
                             ^
                             ,
> +		which can be performed.
                  ^
                that
> +
> +		After each successful update, the number reduces by one. Once it
> +		reaches zero, further updates will fail until next reboot. The
> +		number is always zero if the P-SEAMLDR doesn't support updates.
> +
> +		See Intel® Trust Domain Extensions - SEAM Loader (SEAMLDR)
> +		Interface Specification, Revision 343755-003, Chapter 3.3
> +		"SEAMLDR_INFO" and Chapter 4.2 "SEAMLDR.INSTALL" for more
> +		information.
> diff --git a/drivers/virt/coco/tdx-host/tdx-host.c b/drivers/virt/coco/tdx-host/tdx-host.c
> index 0424933b2560..fd6ffb4f2ff1 100644
> --- a/drivers/virt/coco/tdx-host/tdx-host.c
> +++ b/drivers/virt/coco/tdx-host/tdx-host.c
> @@ -11,6 +11,7 @@
>  #include <linux/sysfs.h>
>  
>  #include <asm/cpu_device_id.h>
> +#include <asm/seamldr.h>
>  #include <asm/tdx.h>
>  
>  static const struct x86_cpu_id tdx_host_ids[] = {
> @@ -40,7 +41,67 @@ static struct attribute *tdx_host_attrs[] = {
>  	&dev_attr_version.attr,
>  	NULL,
>  };
> -ATTRIBUTE_GROUPS(tdx_host);
> +
> +static struct attribute_group tdx_host_group = {
> +	.attrs = tdx_host_attrs,
> +};
> +
> +static ssize_t seamldr_version_show(struct device *dev, struct device_attribute *attr,
> +				    char *buf)
> +{
> +	struct seamldr_info info;
> +	int ret;
> +
> +	ret = seamldr_get_info(&info);
> +	if (ret)
> +		return ret;
> +
> +	return sysfs_emit(buf, "%u.%u.%02u\n", info.major_version,
> +					       info.minor_version,
> +					       info.update_version);
> +}
> +
> +static ssize_t num_remaining_updates_show(struct device *dev,
> +					  struct device_attribute *attr,
> +					  char *buf)
> +{
> +	struct seamldr_info info;
> +	int ret;
> +
> +	ret = seamldr_get_info(&info);
> +	if (ret)
> +		return ret;
> +
> +	return sysfs_emit(buf, "%u\n", info.num_remaining_updates);
> +}
> +
> +/*
> + * Open-code DEVICE_ATTR_ADMIN_RO to specify a different 'show' function
> + * for P-SEAMLDR version as version_show() is used for TDX Module version.
> + *
> + * admin-only readable as reading these attributes calls into P-SEAMLDR,
      ^
      Admin-only
> + * which may have potential performance and system impact.
> + */
> +static struct device_attribute dev_attr_seamldr_version =
> +	__ATTR(version, 0400, seamldr_version_show, NULL);
> +static DEVICE_ATTR_ADMIN_RO(num_remaining_updates);
> +
> +static struct attribute *seamldr_attrs[] = {
> +	&dev_attr_seamldr_version.attr,
> +	&dev_attr_num_remaining_updates.attr,
> +	NULL,
> +};
> +
> +static struct attribute_group seamldr_group = {
> +	.name = "seamldr",
> +	.attrs = seamldr_attrs,
> +};
> +
> +static const struct attribute_group *tdx_host_groups[] = {
> +	&tdx_host_group,
> +	&seamldr_group,
> +	NULL,
> +};
>  
>  static struct faux_device *fdev;
>