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    SubjectRe: [PATCH v2 5/8] iommu: Add PASID support for DMA mapping API users
    Hi Jason,

    On Tue, 15 Mar 2022 11:35:35 -0300, Jason Gunthorpe <jgg@nvidia.com> wrote:

    > On Mon, Mar 14, 2022 at 10:07:09PM -0700, Jacob Pan wrote:
    > > DMA mapping API is the de facto standard for in-kernel DMA. It operates
    > > on a per device/RID basis which is not PASID-aware.
    > >
    > > Some modern devices such as Intel Data Streaming Accelerator, PASID is
    > > required for certain work submissions. To allow such devices use DMA
    > > mapping API, we need the following functionalities:
    > > 1. Provide device a way to retrieve a PASID for work submission within
    > > the kernel
    > > 2. Enable the kernel PASID on the IOMMU for the device
    > > 3. Attach the kernel PASID to the device's default DMA domain, let it
    > > be IOVA or physical address in case of pass-through.
    > >
    > > This patch introduces a driver facing API that enables DMA API
    > > PASID usage. Once enabled, device drivers can continue to use DMA APIs
    > > as is. There is no difference in dma_handle between without PASID and
    > > with PASID.
    > >
    > > Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
    > > drivers/iommu/dma-iommu.c | 65 +++++++++++++++++++++++++++++++++++++++
    > > include/linux/dma-iommu.h | 7 +++++
    > > include/linux/iommu.h | 9 ++++++
    > > 3 files changed, 81 insertions(+)
    > >
    > > diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
    > > index b22034975301..d0ff1a34b1b6 100644
    > > +++ b/drivers/iommu/dma-iommu.c
    > > @@ -39,6 +39,8 @@ enum iommu_dma_cookie_type {
    > > IOMMU_DMA_MSI_COOKIE,
    > > };
    > >
    > > +static DECLARE_IOASID_SET(iommu_dma_pasid);
    > > +
    > > struct iommu_dma_cookie {
    > > enum iommu_dma_cookie_type type;
    > > union {
    > > @@ -370,6 +372,69 @@ void iommu_put_dma_cookie(struct iommu_domain
    > > *domain) domain->iova_cookie = NULL;
    > > }
    > >
    > > +/**
    > > + * iommu_enable_pasid_dma --Enable in-kernel DMA request with PASID
    > > + * @dev: Device to be enabled
    > > + *
    > > + * DMA request with PASID will be mapped the same way as the legacy
    > > DMA.
    > > + * If the device is in pass-through, PASID will also pass-through. If
    > > the
    > > + * device is in IOVA map, the supervisor PASID will point to the same
    > > IOVA
    > > + * page table.
    > > + *
    > > + * @return the kernel PASID to be used for DMA or INVALID_IOASID on
    > > failure
    > > + */
    > > +int iommu_enable_pasid_dma(struct device *dev, ioasid_t *pasid)
    > > +{
    > > + struct iommu_domain *dom;
    > > + ioasid_t id, max;
    > > + int ret;
    > > +
    > > + dom = iommu_get_domain_for_dev(dev);
    > > + if (!dom || !dom->ops || !dom->ops->attach_dev_pasid)
    > > + return -ENODEV;
    >
    > Given the purpose of this API I think it should assert that the device
    > has the DMA API in-use using the machinery from the other series.
    >
    > ie this should not be used to clone non-DMA API iommu_domains..
    >
    Let me try to confirm the specific here. I should check domain type and
    rejects all others except IOMMU_DOMAIN_DMA type, right? Should also allow
    IOMMU_DOMAIN_IDENTITY.

    That makes sense.

    > > diff --git a/include/linux/dma-iommu.h b/include/linux/dma-iommu.h
    > > index 24607dc3c2ac..e6cb9b52a420 100644
    > > +++ b/include/linux/dma-iommu.h
    > > @@ -18,6 +18,13 @@ int iommu_get_dma_cookie(struct iommu_domain
    > > *domain); int iommu_get_msi_cookie(struct iommu_domain *domain,
    > > dma_addr_t base); void iommu_put_dma_cookie(struct iommu_domain
    > > *domain);
    > > +/*
    > > + * For devices that can do DMA request with PASID, setup a system
    > > PASID.
    > > + * Address modes (IOVA, PA) are selected by the platform code.
    > > + */
    > > +int iommu_enable_pasid_dma(struct device *dev, ioasid_t *pasid);
    > > +void iommu_disable_pasid_dma(struct device *dev, ioasid_t pasid);
    >
    > The functions already have a kdoc, don't need two..
    >
    Good point!

    Thanks,

    Jacob

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