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Tue, 17 Mar 2026 06:06:47 -0400 (EDT) Date: Tue, 17 Mar 2026 10:06:40 +0000 From: Kiryl Shutsemau To: Chao Gao Cc: x86@kernel.org, linux-coco@lists.linux.dev, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, binbin.wu@linux.intel.com, dan.j.williams@intel.com, dave.hansen@linux.intel.com, ira.weiny@intel.com, kai.huang@intel.com, nik.borisov@suse.com, paulmck@kernel.org, pbonzini@redhat.com, reinette.chatre@intel.com, rick.p.edgecombe@intel.com, sagis@google.com, seanjc@google.com, tony.lindgren@linux.intel.com, vannapurve@google.com, vishal.l.verma@intel.com, yilun.xu@linux.intel.com Subject: Re: [PATCH v5 06/22] coco/tdx-host: Expose P-SEAMLDR information via sysfs Message-ID: References: <20260315135920.354657-1-chao.gao@intel.com> <20260315135920.354657-7-chao.gao@intel.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20260315135920.354657-7-chao.gao@intel.com> On Sun, Mar 15, 2026 at 06:58:26AM -0700, 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. Register these attributes > during device probe rather than creation, making it easier to hide them > when P-SEAMLDR calls are unsafe (due to CPU erratum). > > Signed-off-by: Chao Gao Reviewed-by: Kiryl Shutsemau (Meta) Few nitpicks below. > --- > v5: > - fix typos [Binbin] > - register seamldr_group during device probe > 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 | 68 ++++++++++++++++++- > 2 files changed, 90 insertions(+), 1 deletion(-) > > diff --git a/Documentation/ABI/testing/sysfs-devices-faux-tdx-host b/Documentation/ABI/testing/sysfs-devices-faux-tdx-host > index 2cf682b65acf..44b8356aed6b 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 etc. > + > +What: /sys/devices/faux/tdx_host/seamldr/version > +Contact: linux-coco@lists.linux.dev > +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@lists.linux.dev > +Description: (RO) Report the number of remaining updates. TDX maintains a > + log about each TDX module that has been loaded. This log has > + a finite size, which limits the number of TDX module updates > + that can be performed. > + > + 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. Do you think revision and chapter numbers useful here? > diff --git a/drivers/virt/coco/tdx-host/tdx-host.c b/drivers/virt/coco/tdx-host/tdx-host.c > index 0424933b2560..8d46e3c039ba 100644 > --- a/drivers/virt/coco/tdx-host/tdx-host.c > +++ b/drivers/virt/coco/tdx-host/tdx-host.c > @@ -11,6 +11,7 @@ > #include > > #include > +#include > #include > > static const struct x86_cpu_id tdx_host_ids[] = { > @@ -42,6 +43,71 @@ static struct attribute *tdx_host_attrs[] = { > }; > ATTRIBUTE_GROUPS(tdx_host); > > +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); Maybe a comment why %02u used for 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, > + * 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 const struct attribute_group seamldr_group = { > + .name = "seamldr", > + .attrs = seamldr_attrs, > +}; > + > +static int seamldr_init(struct device *dev) > +{ > + return devm_device_add_group(dev, &seamldr_group); > +} > + > +static int tdx_host_probe(struct faux_device *fdev) > +{ > + return seamldr_init(&fdev->dev); > +} > + > +static const struct faux_device_ops tdx_host_ops = { > + .probe = tdx_host_probe, > +}; > + > static struct faux_device *fdev; > > static int __init tdx_host_init(void) > @@ -49,7 +115,7 @@ static int __init tdx_host_init(void) > if (!x86_match_cpu(tdx_host_ids) || !tdx_get_sysinfo()) > return -ENODEV; > > - fdev = faux_device_create_with_groups(KBUILD_MODNAME, NULL, NULL, tdx_host_groups); > + fdev = faux_device_create_with_groups(KBUILD_MODNAME, NULL, &tdx_host_ops, tdx_host_groups); > if (!fdev) > return -ENODEV; > > -- > 2.47.3 > -- Kiryl Shutsemau / Kirill A. Shutemov