Re: [PATCH 15/15] PCI/TSM: Add relative MMIO offset support?

[Alexey Kardashevskiy <aik@amd.com>]

On 6/7/26 08:08, Dan Williams wrote:
> The RMM specification, DEN0137-2.0-bet2 section A9.6.2 "Realm validation of
> device memory mappings" documents the expectation that the
> MMIO_REPORTING_OFFSET chosen for TDISP Interface Reports is always BAR
> aligned.
> 
> Ideally this change is not needed and all implementations share the same
> expectation.
> 
> If this semantic is already shipping in production and/or the PCI-SIG
> clarifies that an implementation can hold this assumption then Linux will
> need to ask the TSM drivers for this hint.

We are changing it on SEV-TIO such that the host os calculates the offset to allow TDISP_OFFSET_BAR_ALIGN and passes it to the PSP during TDI_BIND (==interface start), others did not need it in the first place so I guess we can drop this one. Thanks,


> Cc: Alexey Kardashevskiy <aik@amd.com>
> Cc: Xu Yilun <yilun.xu@linux.intel.com>
> Cc: "Aneesh Kumar K.V" <aneesh.kumar@kernel.org>
> Signed-off-by: Dan Williams <djbw@kernel.org>
> ---
>   include/linux/pci-tsm.h | 15 ++++++++++++++-
>   drivers/pci/tsm/core.c  | 14 ++++++++++----
>   2 files changed, 24 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/pci-tsm.h b/include/linux/pci-tsm.h
> index 6d5fadd79360..be9f78ca2c1a 100644
> --- a/include/linux/pci-tsm.h
> +++ b/include/linux/pci-tsm.h
> @@ -296,7 +296,20 @@ struct pci_tsm_devsec *to_pci_tsm_devsec(struct pci_tsm *tsm);
>   int pci_tsm_mmio_setup(struct pci_dev *pdev, struct pci_tsm_mmio *mmio);
>   void pci_tsm_mmio_teardown(struct pci_tsm_mmio *mmio);
>   
> -struct pci_tsm_mmio *pci_tsm_mmio_alloc(struct pci_dev *pdev);
> +/**
> + * enum tdisp_offset_scheme - MMIO_REPORTING_OFFSET assumptions
> + * @TDISP_OFFSET_BAR_ALIGN: mask by bar size to recover offset
> + * @TDISP_OFFSET_RELATIVE: first mmio report per bar is bar-offset-0
> + *
> + * A TSM driver may know that the default TDISP_OFFSET_BAR_ALIGN
> + * assumption is being violated.
> + */
> +enum tdisp_offset_scheme {
> +	TDISP_OFFSET_BAR_ALIGN,
> +	TDISP_OFFSET_RELATIVE,
> +};
> +struct pci_tsm_mmio *pci_tsm_mmio_alloc(struct pci_dev *pdev,
> +					enum tdisp_offset_scheme scheme);
>   int pci_tsm_mmio_free(struct pci_dev *pdev, struct pci_tsm_mmio *mmio);
>   #else
>   static inline int pci_tsm_register(struct tsm_dev *tsm_dev)
> diff --git a/drivers/pci/tsm/core.c b/drivers/pci/tsm/core.c
> index 9ac216ad896d..19ad35f2da4a 100644
> --- a/drivers/pci/tsm/core.c
> +++ b/drivers/pci/tsm/core.c
> @@ -643,13 +643,15 @@ struct pci_tsm_devif_report {
>   /**
>    * pci_tsm_mmio_alloc() - allocate encrypted MMIO range descriptor
>    * @pdev: device owner of MMIO ranges
> + * @scheme: allow the low level TSM driver to hint the offset calc scheme
>    *
>    * Return: the encrypted MMIO range descriptor on success, NULL on failure
>    *
>    * Assumes that this is called within the live lifetime of a PCI device's
>    * association with a low level TSM.
>    */
> -struct pci_tsm_mmio *pci_tsm_mmio_alloc(struct pci_dev *pdev)
> +struct pci_tsm_mmio *pci_tsm_mmio_alloc(struct pci_dev *pdev,
> +					enum tdisp_offset_scheme scheme)
>   {
>   	struct device_evidence *evidence = pdev->tsm->evidence;
>   	u64 reporting_bar_base, last_reporting_end;
> @@ -712,10 +714,14 @@ struct pci_tsm_mmio *pci_tsm_mmio_alloc(struct pci_dev *pdev)
>   			last_bar = bar;
>   
>   			/*
> -			 * Determine the obfuscated base of the BAR. BAR
> -			 * offsets are never obfuscated.
> +			 * Either the first range per bar always maps
> +			 * the start of the BAR, or the reporting_offset
> +			 * is BAR size aligned.
>   			 */
> -			reporting_bar_base = tsm_offset & ~mask;
> +			if (scheme == TDISP_OFFSET_RELATIVE)
> +				reporting_bar_base = tsm_offset;
> +			else
> +				reporting_bar_base = tsm_offset & ~mask;
>   		} else if (tsm_offset < last_reporting_end) {
>   			pci_dbg(pdev, "Reporting ranges within BAR not in ascending order\n");
>   			return NULL;

-- 
Alexey