Re: [PATCH v2 5/8] iommu: Add PASID support for DMA mapping API users

Jacob Pan
2022-03-15T16:34:59Z

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