Re: [PATCH 1/1] iommu/vt-d: Disable PCI ATS in legacy passthrough mode

[Baolu Lu]

On 2023/11/14 9:10, Lu Baolu wrote:
> When IOMMU hardware operates in legacy mode, the TT field of the context
> entry determines the translation type, with three supported types (Section
> 9.3 Context Entry):
>
> - DMA translation without device TLB support
> - DMA translation with device TLB support
> - Passthrough mode with translated and translation requests blocked
>
> Device TLB support is absent when hardware is configured in passthrough
> mode.
>
> Disable the PCI ATS feature when IOMMU is configured for passthrough
> translation type in legacy (non-scalable) mode.
>
> Fixes: 0faa19a1515f ("iommu/vt-d: Decouple PASID & PRI enabling from SVA")
> Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> ---
>   drivers/iommu/intel/iommu.c | 4 ++++
>   1 file changed, 4 insertions(+)
>
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index 11670cd812a3..c3ec09118ab1 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -1413,6 +1413,10 @@ static void iommu_enable_pci_caps(struct device_domain_info *info)
>   	if (!dev_is_pci(info->dev))
>   		return;
>   
> +	if (!sm_supported(info->iommu) && info->domain &&
> +	    domain_type_is_si(info->domain))
> +		return;
> +
>   	pdev = to_pci_dev(info->dev);
>   
>   	/* The PCIe spec, in its wisdom, declares that the behaviour of

Perhaps we could move the check into the caller and make this helper
transparent to the iommu mode and domain type?

diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index 11670cd812a3..9bddd4fbbdf8 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -2492,7 +2492,8 @@ static int dmar_domain_attach_device(struct 
dmar_domain *domain,
                return ret;
        }

-       iommu_enable_pci_caps(info);
+       if (sm_supported(info->iommu) || !domain_type_is_si(info->domain))
+               iommu_enable_pci_caps(info);

        return 0;
 }

Best regards,
baolu