linux-kernel - Re: [PATCH v6 1/4] iommu: Generalize default PCIe requester ID PASID

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Message-ID: <ZHUCGFIpGp5Kku1S@nvidia.com>
Date:   Mon, 29 May 2023 16:50:48 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, iommu@...ts.linux.dev,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>, dmaengine@...r.kernel.org,
        vkoul@...nel.org, Robin Murphy <robin.murphy@....com>,
        Will Deacon <will@...nel.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Raj Ashok <ashok.raj@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>, Yi Liu <yi.l.liu@...el.com>,
        "Yu, Fenghua" <fenghua.yu@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        "Zanussi, Tom" <tom.zanussi@...el.com>,
        narayan.ranganathan@...el.com
Subject: Re: [PATCH v6 1/4] iommu: Generalize default PCIe requester ID PASID

On Fri, May 19, 2023 at 01:32:20PM -0700, Jacob Pan wrote:
> PCIe Process address space ID (PASID) is used to tag DMA traffic, it
> provides finer grained isolation than requester ID (RID).
> 
> For each RID, 0 is as a special PASID for the legacy DMA (without
> PASID), thus RID_PASID. This is universal across all architectures,
> therefore warranted to be declared in the common header.
> Noting that VT-d could support none-zero RID_PASID, but currently not
> used.
> 
> By having a common RID_PASID, we can avoid conflicts between different
> use cases in the generic code. e.g. SVA and DMA API with PASIDs.
> 
> Signed-off-by: Jacob Pan <jacob.jun.pan@...ux.intel.com>
> ---
> v6:
>    - let SMMU code use the common RID_PASID macro
> ---
>  .../iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c   |  2 +-
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c   | 10 ++++----
>  drivers/iommu/intel/iommu.c                   | 24 +++++++++----------
>  drivers/iommu/intel/pasid.c                   |  2 +-
>  drivers/iommu/intel/pasid.h                   |  1 -
>  include/linux/iommu.h                         |  1 +
>  6 files changed, 20 insertions(+), 20 deletions(-)

I tend to agree with Jean-Philippe's remarks on the name

This is the "untagged" DMA for environments that have optional tags.

Otherwise:

Reviewed-by: Jason Gunthorpe <jgg@...dia.com>

Jason