RE: [PATCH V2 4/4] intel-iommu: PASID support

[Tian, Kevin]

> From: Jason Wang
> Sent: Monday, March 21, 2022 1:54 PM
> 
> +    /*
> +     * vtd-spec v3.4 3.14:
> +     *
> +     * """
> +     * Requests-with-PASID with input address in range 0xFEEx_xxxx are
> +     * translated normally like any other request-with-PASID through
> +     * DMA-remapping hardware. However, if such a request is processed
> +     * using pass-through translation, it will be blocked as described
> +     * in the paragraph below.

While PASID+PT is blocked as described in the below paragraph, the
paragraph itself applies to all situations:

  1) PT + noPASID
  2) translation + noPASID
  3) PT + PASID
  4) translation + PASID

because...

> +     *
> +     * Software must not program paging-structure entries to remap any
> +     * address to the interrupt address range. Untranslated requests
> +     * and translation requests that result in an address in the
> +     * interrupt range will be blocked with condition code LGN.4 or
> +     * SGN.8.

... if you look at the definition of LGN.4 or SGN.8:

LGN.4:  When legacy mode (RTADDR_REG.TTM=00b) is enabled, hardware
        detected an output address (i.e. address after remapping) in the
        interrupt address range (0xFEEx_xxxx). For Translated requests and
        requests with pass-through translation type (TT=10), the output
        address is the same as the address in the request

The last sentence in the first paragraph above just highlights the fact that
when input address of PT is in interrupt range then it is blocked by LGN.4
or SGN.8 due to output address also in interrupt range.

> +     * """
> +     *
> +     * We enable per as memory region (iommu_ir_fault) for catching
> +     * the tranlsation for interrupt range through PASID + PT.
> +     */
> +    if (pt && as->pasid != PCI_NO_PASID) {
> +        memory_region_set_enabled(&as->iommu_ir_fault, true);
> +    } else {
> +        memory_region_set_enabled(&as->iommu_ir_fault, false);
> +    }
> +

Given above this should be a bug fix for nopasid first and then apply it
to pasid path too.

Thanks
Kevin