Re: [PATCH 2/7] PCI/TSM: Add pci_tsm_guest_req() for managing TDIs

[Aneesh Kumar K.V <aneesh.kumar@kernel.org>]

Dan Williams <dan.j.williams@intel.com> writes:

> +/** 
> + * enum pci_tsm_req_scope - Scope of guest requests to be validated by TSM
> + *
> + * Guest requests are a transport for a TVM to communicate with a TSM + DSM for
> + * a given TDI. A TSM driver is responsible for maintaining the kernel security
> + * model and limit commands that may affect the host, or are otherwise outside
> + * the typical TDISP operational model.
> + */
> +enum pci_tsm_req_scope {
> +	/**
> +	 * @PCI_TSM_REQ_INFO: Read-only, without side effects, request for
> +	 * typical TDISP collateral information like Device Interface Reports.
> +	 * No device secrets are permitted, and no device state is changed.
> +	 */
> +	PCI_TSM_REQ_INFO = 0,
> +	/**
> +	 * @PCI_TSM_REQ_STATE_CHANGE: Request to change the TDISP state from
> +	 * UNLOCKED->LOCKED, LOCKED->RUN. No any other device state,
> +	 * configuration, or data change is permitted.
> +	 */
> +	PCI_TSM_REQ_STATE_CHANGE = 1,
> +	/**
> +	 * @PCI_TSM_REQ_DEBUG_READ: Read-only request for debug information
> +	 *
> +	 * A method to facilitate TVM information retrieval outside of typical
> +	 * TDISP operational requirements. No device secrets are permitted.
> +	 */
> +	PCI_TSM_REQ_DEBUG_READ = 2,
> +	/**
> +	 * @PCI_TSM_REQ_DEBUG_WRITE: Device state changes for debug purposes
> +	 *
> +	 * The request may affect the operational state of the device outside of
> +	 * the TDISP operational model. If allowed, requires CAP_SYS_RAW_IO, and
> +	 * will taint the kernel.
> +	 */
> +	PCI_TSM_REQ_DEBUG_WRITE = 3,
> +};
> +

Will all architectures need to support all the above pci_tsm_req_scope
values?

For example, on ARM, I’ve implemented a simpler approach [1] by using an
architecture-specific pci_tsm_req_scope / type. This simplifies
the implementation, as I can access `info->req` and `info->resp`
directly within the same callback, without needing an additional
structure to carry arch-specific request types like
`ARM_CCA_DA_OBJECT_SIZE` or `ARM_CCA_DA_OBJECT_READ`.

[1] https://git.gitlab.arm.com/linux-arm/linux-cca/-/commit/ae6e667a6426fdeff9cdf9f6807acb8a5d5d601f

-aneesh