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Peter Anvin" , Ingo Molnar , Jonathan Corbet , Shuah Khan , Thomas Gleixner Subject: [PATCH v5 00/22] Runtime TDX module update support Date: Sun, 15 Mar 2026 06:58:20 -0700 Message-ID: <20260315135920.354657-1-chao.gao@intel.com> X-Mailer: git-send-email 2.47.3 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Hi Reviewers, With this posting, I'm hoping to collect more Reviewed-by or Acked-by tags. Please note these changes: Patch 18 handles a CPU erratum that clears the active VMCS after P-SEAMLDR calls. Because of this erratum, patch 6 now exposes seamldr attributes during device probe rather than creation as unconditional exposure would be unsafe. Patch 22 adds error logging for update failures. It's kind of nice-to-have, so it is placed last for easy removal if necessary. For transparency, I should note that I used an Intel-operated AI tool to help proofread this cover-letter and commit messages. Changelog: v4->v5: - s/TDX Module/TDX module/g [Binbin/Dave] - drop is_vmalloc_addr() checking [Dave/Rick] - protect lockstep control data with a lock [Dave] - clarify why raw_spinlock is used [Dave/Kai] - drop patches that check all CPUs are online and updates are not exhauste= d [Dave] - register seamldr attributes in device probe - use devm_add_action_or_reset for seamldr deinit [Yilun] - remove global tdx_fw [Yilun] - clarify request_firmware() doesn't take filename from userspace [Rick] - drop unnecessary checks when populating an update request [Rick] - rewrite the commit message for the skeleton patch - rewrite the commit message for the "update-sensitive operations" handlin= g patch - other minor code changes, changelog improvements and typo fixes [Binbin/= Yan etc] - collect review tags from Yilun/Rick/Kai/Binbin - v4: https://lore.kernel.org/kvm/20260212143606.534586-1-chao.gao@intel.c= om/ This series adds support for runtime TDX module updates that preserve running TDX guests. It is also available at: https://github.com/gaochaointel/linux-dev/commits/tdx-module-updates-v5/ =3D=3D Background =3D=3D Intel TDX isolates Trusted Domains (TDs), or confidential guests, from the host. A key component of Intel TDX is the TDX module, which enforces security policies to protect the memory and CPU states of TDs from the host. However, the TDX module is software that requires updates. =3D=3D Problems =3D=3D Currently, the TDX module is loaded by the BIOS at boot time, and the only way to update it is through a reboot, which results in significant system downtime. Users expect the TDX module to be updatable at runtime without disrupting TDX guests. =3D=3D Solution =3D=3D On TDX platforms, P-SEAMLDR[1] is a component within the protected SEAM range. It is loaded by the BIOS and provides the host with functions to install a TDX module at runtime. Implement a TDX module update facility via the fw_upload mechanism. Given that there is variability in which module update to load based on features, fix levels, and potentially reloading the same version for error recovery scenarios, the explicit userspace chosen payload flexibility of fw_upload is attractive. This design allows the kernel to accept a bitstream instead of loading a named file from the filesystem, as the module selection and policy enforcement for TDX modules are quite complex (see patch "coco/tdx-host: Implement firmware upload sysfs ABI for TDX module updates"). By doing so, much of this complexity is shifted out of the kernel. The kernel needs to expose information, such as the TDX module version, to userspace. Userspace must understand the TDX module versioning scheme and update policy to select the appropriate TDX module (see "TDX module Versioning" below). In the unlikely event the update fails, for example userspace picks an incompatible update image, or the image is otherwise corrupted, all TDs will experience SEAMCALL failures and be killed. The recovery of TD operation from that event requires a reboot. Given there is no mechanism to quiesce SEAMCALLs, the TDs themselves must pause execution over an update. The most straightforward way to meet the 'pause TDs while update executes' constraint is to run the update in stop_machine() context. All other evaluated solutions export more complexity to KVM, or exports more fragility to userspace. =3D=3D How to test this series =3D=3D First, load kvm-intel.ko and tdx-host.ko if they haven't been loaded: # modprobe -r kvm_intel # modprobe kvm_intel tdx=3D1 # modprobe tdx-host Then, use the userspace tool below to select the appropriate TDX module and install it via the interfaces exposed by this series: # git clone https://github.com/intel/tdx-module-binaries # cd tdx-module-binaries # python version_select_and_load.py --update this version changes the firmware directory name from seamldr_upload to tdx_module, so, below change should be applied to version_select_and_load.p= y: diff --git a/version_select_and_load.py b/version_select_and_load.py index 2193bd8..6a3b604 100644 --- a/version_select_and_load.py +++ b/version_select_and_load.py @@ -38,7 +38,7 @@ except ImportError: print("Error: cpuid module is not installed. Please install it using '= pip install cpuid'") sys.exit(1) -FIRMWARE_PATH =3D "/sys/class/firmware/seamldr_upload" +FIRMWARE_PATH =3D "/sys/class/firmware/tdx_module" MODULE_PATH =3D "/sys/devices/faux/tdx_host" SEAMLDR_PATH =3D "/sys/devices/faux/tdx_host/seamldr" allow_debug =3D False =3D=3D Other information relevant to Runtime TDX module updates =3D=3D =3D=3D=3D TDX module versioning =3D=3D=3D Each TDX module is assigned a version number x.y.z, where x represents the "major" version, y the "minor" version, and z the "update" version. Runtime TDX module updates are restricted to Z-stream releases. Note that Z-stream releases do not necessarily guarantee compatibility. A new release may not be compatible with all previous versions. To address th= is, Intel provides a separate file containing compatibility information, which specifies the minimum module version required for a particular update. This information is referenced by the tool to determine if two modules are compatible. =3D=3D=3D TCB Stability =3D=3D=3D Updates change the TCB as viewed by attestation reports. In TDX there is a distinction between launch-time version and current version where runtime TDX module updates cause that latter version number to change, subject to Z-stream constraints. The concern that a malicious host may attack confidential VMs by loading insecure updates was addressed by Alex in [3]. Similarly, the scenario where some "theoretical paranoid tenant" in the cloud wants to audit updates and stop trusting the host after updates until audit completion was also addressed in [4]. Users not in the cloud control the host machine and can manage updates themselves, so they don't have these concerns. See more about the implications of current TCB version changes in attestation as summarized by Dave in [5]. =3D=3D=3D TDX module Distribution Model =3D=3D=3D At a high level, Intel publishes all TDX modules on the github [2], along with a mapping_file.json which documents the compatibility information about each TDX module and a userspace tool to install the TDX module. OS vendors can package these modules and distribute them. Administrators install the package and use the tool to select the appropriate TDX module and install it via the interfaces exposed by this series. [1]: https://cdrdv2.intel.com/v1/dl/getContent/733584 [2]: https://github.com/intel/tdx-module-binaries [3]: https://lore.kernel.org/all/665c5ae0-4b7c-4852-8995-255adf7b3a2f@amazo= n.com/ [4]: https://lore.kernel.org/all/5d1da767-491b-4077-b472-2cc3d73246d6@amazo= n.com/ [5]: https://lore.kernel.org/all/94d6047e-3b7c-4bc1-819c-85c16ff85abf@intel= .com/ Chao Gao (21): coco/tdx-host: Introduce a "tdx_host" device coco/tdx-host: Expose TDX module version x86/virt/seamldr: Introduce a wrapper for P-SEAMLDR SEAMCALLs x86/virt/seamldr: Retrieve P-SEAMLDR information coco/tdx-host: Expose P-SEAMLDR information via sysfs coco/tdx-host: Implement firmware upload sysfs ABI for TDX module updates x86/virt/seamldr: Allocate and populate a module update request x86/virt/seamldr: Introduce skeleton for TDX module updates x86/virt/seamldr: Abort updates if errors occurred midway x86/virt/seamldr: Shut down the current TDX module x86/virt/tdx: Reset software states during TDX module shutdown x86/virt/seamldr: Install a new TDX module x86/virt/seamldr: Do TDX per-CPU initialization after updates x86/virt/tdx: Restore TDX module state x86/virt/tdx: Update tdx_sysinfo and check features post-update x86/virt/tdx: Avoid updates during update-sensitive operations coco/tdx-host: Don't expose P-SEAMLDR features on CPUs with erratum x86/virt/tdx: Enable TDX module runtime updates coco/tdx-host: Document TDX module update compatibility criteria x86/virt/tdx: Document TDX module update x86/virt/seamldr: Log TDX module update failures Kai Huang (1): x86/virt/tdx: Move low level SEAMCALL helpers out of .../ABI/testing/sysfs-devices-faux-tdx-host | 75 ++++ Documentation/arch/x86/tdx.rst | 36 ++ arch/x86/include/asm/cpufeatures.h | 1 + arch/x86/include/asm/seamldr.h | 37 ++ arch/x86/include/asm/tdx.h | 65 +--- arch/x86/include/asm/tdx_global_metadata.h | 5 + arch/x86/include/asm/vmx.h | 1 + arch/x86/kvm/vmx/tdx_errno.h | 2 - arch/x86/virt/vmx/tdx/Makefile | 2 +- arch/x86/virt/vmx/tdx/seamcall_internal.h | 109 ++++++ arch/x86/virt/vmx/tdx/seamldr.c | 325 ++++++++++++++++++ arch/x86/virt/vmx/tdx/tdx.c | 165 ++++++--- arch/x86/virt/vmx/tdx/tdx.h | 11 +- arch/x86/virt/vmx/tdx/tdx_global_metadata.c | 18 + drivers/virt/coco/Kconfig | 2 + drivers/virt/coco/Makefile | 1 + drivers/virt/coco/tdx-host/Kconfig | 12 + drivers/virt/coco/tdx-host/Makefile | 1 + drivers/virt/coco/tdx-host/tdx-host.c | 228 ++++++++++++ 19 files changed, 995 insertions(+), 101 deletions(-) create mode 100644 Documentation/ABI/testing/sysfs-devices-faux-tdx-host create mode 100644 arch/x86/include/asm/seamldr.h create mode 100644 arch/x86/virt/vmx/tdx/seamcall_internal.h create mode 100644 arch/x86/virt/vmx/tdx/seamldr.c create mode 100644 drivers/virt/coco/tdx-host/Kconfig create mode 100644 drivers/virt/coco/tdx-host/Makefile create mode 100644 drivers/virt/coco/tdx-host/tdx-host.c --=20 2.47.3