linux-kernel - Re: [PATCH v12 1/8] iommu: Generalize PASID 0 for normal DMA w/o PASID

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Date:   Fri, 4 Aug 2023 10:51:59 -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>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Robin Murphy <robin.murphy@....com>,
        Will Deacon <will@...nel.org>,
        "Tian, Kevin" <kevin.tian@...el.com>, Yi Liu <yi.l.liu@...el.com>,
        "Yu, Fenghua" <fenghua.yu@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>
Subject: Re: [PATCH v12 1/8] iommu: Generalize PASID 0 for normal DMA w/o
 PASID

On Wed, Aug 02, 2023 at 02:24:20PM -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 device/RID, 0 is a special PASID for the normal DMA (no
> PASID). This is universal across all architectures that supports PASID,
> therefore warranted to be reserved globally and declared in the common
> header. Consequently, we can avoid the conflict between different PASID
> use cases in the generic code. e.g. SVA and DMA API with PASIDs.
> 
> This paved away for device drivers to choose global PASID policy while
> continue doing normal DMA.
> 
> Noting that VT-d could support none-zero RID/NO_PASID, but currently not
> used.
> 
> Reviewed-by: Lu Baolu <baolu.lu@...ux.intel.com>
> Reviewed-by: Kevin Tian <kevin.tian@...el.com>
> Reviewed-by: Jean-Philippe Brucker <jean-philippe@...aro.org>
> Signed-off-by: Jacob Pan <jacob.jun.pan@...ux.intel.com>
> ---
> v8:
>    - make consistent use of NO_PASID in SMMU code
>    - remove PASID_MIN
> v7:
>    - renamed IOMMU_DEF_RID_PASID to be IOMMU_NO_PASID to be more generic
> 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   | 16 ++++++-------
>  drivers/iommu/intel/iommu.c                   | 24 +++++++++----------
>  drivers/iommu/intel/pasid.c                   |  2 +-
>  drivers/iommu/intel/pasid.h                   |  2 --
>  include/linux/iommu.h                         |  1 +
>  6 files changed, 23 insertions(+), 24 deletions(-)

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

Jason