For TDX Module updates, userspace needs to select compatible update versions based on the current module version. This design delegates module selection complexity to userspace because TDX Module update policies are complex and version series are platform-specific. For example, the 1.5.x series is for certain platform generations, while the 2.0.x series is intended for others. And TDX Module 1.5.x may be updated to 1.5.y but not to 1.5.y+1. Expose the TDX Module version to userspace via sysfs to aid module selection. Since the TDX faux device will drive module updates, expose the version as its attribute. One bonus of exposing TDX Module version via sysfs is: TDX Module version information remains available even after dmesg logs are cleared. == Background == The "faux device + device attribute" approach compares to other update mechanisms as follows: 1. AMD SEV leverages an existing PCI device for the PSP to expose metadata. TDX uses a faux device as it doesn't have PCI device in its architecture. 2. Microcode uses per-CPU virtual devices to report microcode revisions because CPUs can have different revisions. But, there is only a single TDX Module, so exposing the TDX Module version through a global TDX faux device is appropriate 3. ARM's CCA implementation isn't in-tree yet, but will likely follow a similar faux device approach [1], though it's unclear whether they need to expose firmware version information Signed-off-by: Chao Gao Reviewed-by: Binbin Wu Reviewed-by: Tony Lindgren Reviewed-by: Xu Yilun Link: https://lore.kernel.org/all/2025073035-bulginess-rematch-b92e@gregkh/ # [1] --- v4: - collect reviews - Explain other version exposure implementations and why tdx's approach differs from them v3: - Justify the sysfs ABI choice and expand background on other CoCo implementations. --- .../ABI/testing/sysfs-devices-faux-tdx-host | 6 +++++ drivers/virt/coco/tdx-host/tdx-host.c | 26 ++++++++++++++++++- 2 files changed, 31 insertions(+), 1 deletion(-) create mode 100644 Documentation/ABI/testing/sysfs-devices-faux-tdx-host diff --git a/Documentation/ABI/testing/sysfs-devices-faux-tdx-host b/Documentation/ABI/testing/sysfs-devices-faux-tdx-host new file mode 100644 index 000000000000..901abbae2e61 --- /dev/null +++ b/Documentation/ABI/testing/sysfs-devices-faux-tdx-host @@ -0,0 +1,6 @@ +What: /sys/devices/faux/tdx_host/version +Contact: linux-coco@lists.linux.dev +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. diff --git a/drivers/virt/coco/tdx-host/tdx-host.c b/drivers/virt/coco/tdx-host/tdx-host.c index c77885392b09..0424933b2560 100644 --- a/drivers/virt/coco/tdx-host/tdx-host.c +++ b/drivers/virt/coco/tdx-host/tdx-host.c @@ -8,6 +8,7 @@ #include #include #include +#include #include #include @@ -18,6 +19,29 @@ static const struct x86_cpu_id tdx_host_ids[] = { }; MODULE_DEVICE_TABLE(x86cpu, tdx_host_ids); +static ssize_t version_show(struct device *dev, struct device_attribute *attr, + char *buf) +{ + const struct tdx_sys_info *tdx_sysinfo = tdx_get_sysinfo(); + const struct tdx_sys_info_version *ver; + + if (!tdx_sysinfo) + return -ENXIO; + + ver = &tdx_sysinfo->version; + + return sysfs_emit(buf, "%u.%u.%02u\n", ver->major_version, + ver->minor_version, + ver->update_version); +} +static DEVICE_ATTR_RO(version); + +static struct attribute *tdx_host_attrs[] = { + &dev_attr_version.attr, + NULL, +}; +ATTRIBUTE_GROUPS(tdx_host); + static struct faux_device *fdev; static int __init tdx_host_init(void) @@ -25,7 +49,7 @@ static int __init tdx_host_init(void) if (!x86_match_cpu(tdx_host_ids) || !tdx_get_sysinfo()) return -ENODEV; - fdev = faux_device_create(KBUILD_MODNAME, NULL, NULL); + fdev = faux_device_create_with_groups(KBUILD_MODNAME, NULL, NULL, tdx_host_groups); if (!fdev) return -ENODEV; -- 2.47.3