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

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Message-ID: <20220315143535.GX11336@nvidia.com>
Date:   Tue, 15 Mar 2022 11:35:35 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc:     iommu@...ts.linux-foundation.org,
        LKML <linux-kernel@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>,
        Christoph Hellwig <hch@...radead.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Jacob Pan <jacob.jun.pan@...el.com>,
        Raj Ashok <ashok.raj@...el.com>,
        "Kumar, Sanjay K" <sanjay.k.kumar@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        "Zanussi, Tom" <tom.zanussi@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>, Yi Liu <yi.l.liu@...el.com>
Subject: Re: [PATCH v2 5/8] iommu: Add PASID support for DMA mapping API users

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@...ux.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..

> 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..

Jason