tl;dr: Select fw_upload for doing TDX module updates. The process of
selecting among available update images is complicated and nuanced. Punt
the selection process out to userspace. One existing userspace
implementation today is the script in the Intel TDX Module Binaries
repository[1].
Long Version:
The kernel supports two primary firmware update mechanisms:
1. request_firmware() - used by microcode, SEV firmware, hundreds of
other drivers
2. 'struct fw_upload' - used by CXL, FPGA updates, dozens of others
The key difference between is that request_firmware() loads a named file
from the filesystem where the filename is kernel-controlled, while
fw_upload accepts firmware data directly from userspace.
TDX module firmware update selection policy is too complex for the kernel.
Leave it to userspace and use fw_upload.
Add a skeleton fw_upload implementation to be fleshed out in subsequent
patches.
Refactor the sysfs visiblity attribute function so it can be used as a
more generic flag for the presence of viable runtime update support.
Why fw_upload instead of request_firmware()?
============================================
Selecting a TDX module update image is not a simple "load the latest"
decision. Userspace needs to choose an image that is compatible with both
the platform and the currently running module.
Some constraints are hard requirements:
a. Module version series are platform-specific. For example, the 1.5.x
series runs on Sapphire Rapids but not Granite Rapids, which needs
2.0.x.
b. Updates are also constrained by version distance. A 1.5.6 module
might permit updates to 1.5.7 but not to 1.5.50.
There may also be userspace policy choices:
c. Decide the update direction: upgrade or downgrade
d. Choose whether to optimize for fewer updates or smaller version
steps, for example, 1.2.3=>1.2.5 versus 1.2.3=>1.2.4=>1.2.5.
Given that complexity, leave module selection to userspace and use
fw_upload.
1. https://github.com/intel/confidential-computing.tdx.tdx-module.binaries/blob/main/version_select_and_load.py
[ dhansen: add version script link, add more explanation of code moves,
fix some minor whitespace issues ]
Signed-off-by: Chao Gao <chao.gao@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Tony Lindgren <tony.lindgren@linux.intel.com>
Reviewed-by: Kai Huang <kai.huang@intel.com>
Reviewed-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
Link: https://lore.kernel.org/kvm/01fc8946-eb84-46fa-9458-f345dd3f6033@intel.com/
Link: https://patch.msgid.link/20260520133909.409394-13-chao.gao@intel.com
TDX depends on a platform firmware module that runs on the CPU.
Unlike other CoCo architectures, TDX has no hardware "device"
running the show, just a blob on the CPU.
Create a virtual device to anchor interactions with this platform
firmware. This lets later code:
- expose metadata: TDX module version, seamldr version, to userspace
as device attributes
- implement firmware uploader APIs (which are tied to a device) to
support TDX module runtime updates
Use a faux device because the TDX module is singular within the system
and has no platform resources. Using a faux device eliminates the need
to create a stub bus.
The call to tdx_get_sysinfo() ensures that the TDX module is ready to
provide services.
Note that AMD has a PCI device for the PSP for SEV and ARM CCA will
likely have a faux device [1].
Thanks to Dan and Yilun for all the help on this one.
[ dhansen: trim changelog ]
Signed-off-by: Chao Gao <chao.gao@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Reviewed-by: Tony Lindgren <tony.lindgren@linux.intel.com>
Reviewed-by: Xu Yilun <yilun.xu@linux.intel.com>
Reviewed-by: Kai Huang <kai.huang@intel.com>
Reviewed-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Link: https://lore.kernel.org/all/2025073035-bulginess-rematch-b92e@gregkh/ # [1]
Link: https://patch.msgid.link/20260520133909.409394-7-chao.gao@intel.com
