Re: [PATCH v2 15/31] coco/tdx-host: Introduce a "tdx_host" device

[Ackerley Tng]

Xu Yilun <yilun.xu@xxxxxxxxxxxxxxx> writes:

> From: Chao Gao <chao.gao@xxxxxxxxx>
>
> TDX depends on a platform firmware module that is invoked via instructions
> similar to vmenter (i.e. enter into a new privileged "root-mode" context to
> manage private memory and private device mechanisms). It is a software
> construct that depends on the CPU vmxon state to enable invocation of
> TDX module ABIs. Unlike other Trusted Execution Environment (TEE) platform
> implementations that employ a firmware module running on a PCI device with
> an MMIO mailbox for communication, TDX has no hardware device to point to
> as the TEE Secure Manager (TSM).
>

I'm trying to get up to speed on Confidential IO. Thank you for this
summary!

s/TEE Secure Manager (TSM)/TEE Security Manager/

> Create a virtual device not only to align with other implementations but
> also to make it easier to
>
>  - expose metadata (e.g., TDX module version, seamldr version etc) to
>    the userspace as device attributes
>
>  - implement firmware uploader APIs which are tied to a device. This is
>    needed to support TDX module runtime updates
>
>  - enable TDX Connect which will share a common infrastructure with other
>    platform implementations. In the TDX Connect context, every
>    architecture has a TSM, represented by a PCIe or virtual device. The
>    new "tdx_host" device will serve the TSM role.
>
> A faux device is used for TDX because the TDX module is singular within
> the system and lacks associated 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].
>
> Co-developed-by: Xu Yilun <yilun.xu@xxxxxxxxxxxxxxx>
> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
> Signed-off-by: Chao Gao <chao.gao@xxxxxxxxx>
> Reviewed-by: Jonathan Cameron <jonathan.cameron@xxxxxxxxxx>
> Reviewed-by: Tony Lindgren <tony.lindgren@xxxxxxxxxxxxxxx>
> Reviewed-by: Xu Yilun <yilun.xu@xxxxxxxxxxxxxxx>
> Reviewed-by: Kai Huang <kai.huang@xxxxxxxxx>
> Reviewed-by: Kiryl Shutsemau (Meta) <kas@xxxxxxxxxx>
> Link: https://lore.kernel.org/all/2025073035-bulginess-rematch-b92e@gregkh/ # [1]
> Signed-off-by: Xu Yilun <yilun.xu@xxxxxxxxxxxxxxx>
>
> [...snip...]
>