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Peter Anvin" , Sebastian Andrzej Siewior , Clark Williams , Steven Rostedt , Jonathan Corbet , Shuah Khan Subject: [PATCH v8 00/21] Runtime TDX module update support Date: Mon, 27 Apr 2026 08:27:54 -0700 Message-ID: <20260427152854.101171-1-chao.gao@intel.com> X-Mailer: git-send-email 2.52.0 Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Hi Reviewers, This v8 mainly addresses issues raised by Rick and collects his Reviewed-by tags. The most notable changes are removing pieces that are not strictly needed for the basic runtime update support and tightening several commit messages to make them more direct and to the point. In particular, patches 08 and 15 were substantially rewritten, and commit messages for patches 16 and 17 were reworked, so those would benefit from another review. The rest of the series has only minor changes. I'm hoping this series can be merged for 7.2. Changelog: v7->v8: - rebase onto v7.1-rc1 to resolve conflicts with the merged VMXON series - flatten the P-SEAMLDR sysfs ABI by exposing seamldr_version and num_remaining_updates directly under /sys/devices/faux/tdx_host/, and clarify when they are visible - don't preemptively handle "PAGE_SIZE != 4KB" case - tighten the fw_upload ABI: return FW_UPLOAD_ERR_BUSY for TD-build contention and collapse other update failures to firmware-invalid - consolidate tdx_blob validation in a separate function and clarify what is validated by the kernel vs. P-SEAMLDR - rework the changelog of aborting updates on any failure; always use READ_ONCE()/WRITE_ONCE() for the shared "failed" flag access - rewrite the changelog of handling the race between updates and TD builds; always pass the compat flag to TDH.SYS.SHUTDOWN - refresh only the TDX module update_version after a successful update; drop the broader post-update metadata/feature checks - explain the kernel's role and responsibilities in TDX module updates in the cover letter - collect new review/ack tags - minor typo and wording fixes - v7: https://lore.kernel.org/kvm/20260331124214.117808-1-chao.gao@intel.com/ (For transparency, note that I used AI tools to help proofread this cover-letter and commit messages) 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-v8/ == Background == 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. == Problems == 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. == Solution == 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. This series implements runtime TDX module updates through the fw_upload mechanism. That interface is a good fit because TDX module selection is not a simple "load a known file from disk" problem. The update image to load depends on module versioning, compatibility rules. fw_upload lets userspace choose the module explicitly while the kernel provides the update mechanism. This design intentionally keeps most update validation/policy in userspace. The kernel exposes the information userspace needs, such as TDX module version and P-SEAMLDR information, but userspace is responsible for understanding TDX module's versioning and compatibility rules and for choosing an appropriate update image (see "TDX module versioning" below). The kernel still enforces the pieces that must be handled in-kernel: 1. Validate the tdx_blob header fields that are not passed through tothe TDX module. Just the standard overflow and reserved bits defensive ABI stuff. 2. Make sure no non-update SEAMCALLs are called during the update. 3. Make sure SEAMCALLs are on the right CPU, for any the user has made available to the kernel. 4. Handle the race between updates and concurrent TD builds by returning -EBUSY to userspace. Everything else remains a userspace responsibility. 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. == How to test this series == 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 == Other information relevant to Runtime TDX module updates == === TDX module versioning === 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 this, 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. === TCB Stability === 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]. === TDX module Distribution Model === 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@amazon.com/ [4]: https://lore.kernel.org/all/5d1da767-491b-4077-b472-2cc3d73246d6@amazon.com/ [5]: https://lore.kernel.org/all/94d6047e-3b7c-4bc1-819c-85c16ff85abf@intel.com/ Chao Gao (20): 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: Add a helper to 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: 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 module installation x86/virt/tdx: Restore TDX module state x86/virt/tdx: Refresh TDX module version after update x86/virt/tdx: Reject updates during concurrent TD build x86/virt/seamldr: Abort updates on failure 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 Kai Huang (1): x86/virt/tdx: Move low level SEAMCALL helpers out of .../ABI/testing/sysfs-devices-faux-tdx-host | 67 ++++ 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 | 69 ++-- arch/x86/include/asm/tdx_global_metadata.h | 4 + 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 | 330 ++++++++++++++++++ arch/x86/virt/vmx/tdx/tdx.c | 157 ++++++--- arch/x86/virt/vmx/tdx/tdx.h | 9 +- arch/x86/virt/vmx/tdx/tdx_global_metadata.c | 17 +- 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 | 221 ++++++++++++ 19 files changed, 970 insertions(+), 108 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 base-commit: 254f49634ee16a731174d2ae34bc50bd5f45e731 -- 2.47.1