Re: [PATCH v3 2/4] iommu: Add PASID support for DMA mapping API users

[Jason Gunthorpe <jgg@nvidia.com>]

On Tue, May 10, 2022 at 02:07:02PM -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 | 107 ++++++++++++++++++++++++++++++++++++++
>  include/linux/dma-iommu.h |   3 ++
>  include/linux/iommu.h     |   2 +
>  3 files changed, 112 insertions(+)
> 
> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> index 1ca85d37eeab..5984f3129fa2 100644
> +++ b/drivers/iommu/dma-iommu.c
> @@ -34,6 +34,8 @@ struct iommu_dma_msi_page {
>  	phys_addr_t		phys;
>  };
>  
> +static DECLARE_IOASID_SET(iommu_dma_pasid);
> +
>  enum iommu_dma_cookie_type {
>  	IOMMU_DMA_IOVA_COOKIE,
>  	IOMMU_DMA_MSI_COOKIE,
> @@ -370,6 +372,111 @@ void iommu_put_dma_cookie(struct iommu_domain *domain)
>  	domain->iova_cookie = NULL;
>  }
>  
> +/**
> + * iommu_attach_dma_pasid --Attach a PASID for in-kernel DMA. Use the device's
> + * DMA domain.
> + * @dev: Device to be enabled
> + * @pasid: The returned kernel PASID to be used for DMA
> + *
> + * 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, the PASID will point to the same IOVA page table.
> + *
> + * @return err code or 0 on success
> + */
> +int iommu_attach_dma_pasid(struct device *dev, ioasid_t *pasid)
> +{
> +	struct iommu_domain *dom;
> +	ioasid_t id, max;
> +	int ret = 0;
> +
> +	dom = iommu_get_domain_for_dev(dev);
> +	if (!dom || !dom->ops || !dom->ops->attach_dev_pasid)
> +		return -ENODEV;
> +
> +	/* Only support domain types that DMA API can be used */
> +	if (dom->type == IOMMU_DOMAIN_UNMANAGED ||
> +	    dom->type == IOMMU_DOMAIN_BLOCKED) {
> +		dev_warn(dev, "Invalid domain type %d", dom->type);

This should be a WARN_ON

> +		return -EPERM;
> +	}
> +
> +	id = dom->pasid;
> +	if (!id) {
> +		/*
> +		 * First device to use PASID in its DMA domain, allocate
> +		 * a single PASID per DMA domain is all we need, it is also
> +		 * good for performance when it comes down to IOTLB flush.
> +		 */
> +		max = 1U << dev->iommu->pasid_bits;
> +		if (!max)
> +			return -EINVAL;
> +
> +		id = ioasid_alloc(&iommu_dma_pasid, 1, max, dev);
> +		if (id == INVALID_IOASID)
> +			return -ENOMEM;
> +
> +		dom->pasid = id;
> +		atomic_set(&dom->pasid_users, 1);

All of this needs proper locking.

> +	}
> +
> +	ret = dom->ops->attach_dev_pasid(dom, dev, id);
> +	if (!ret) {
> +		*pasid = id;
> +		atomic_inc(&dom->pasid_users);
> +		return 0;
> +	}
> +
> +	if (atomic_dec_and_test(&dom->pasid_users)) {
> +		ioasid_free(id);
> +		dom->pasid = 0;
> +	}
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL(iommu_attach_dma_pasid);
> +
> +/**
> + * iommu_detach_dma_pasid --Disable in-kernel DMA request with PASID
> + * @dev:	Device's PASID DMA to be disabled
> + *
> + * It is the device driver's responsibility to ensure no more incoming DMA
> + * requests with the kernel PASID before calling this function. IOMMU driver
> + * ensures PASID cache, IOTLBs related to the kernel PASID are cleared and
> + * drained.
> + *
> + */
> +void iommu_detach_dma_pasid(struct device *dev)
> +{
> +	struct iommu_domain *dom;
> +	ioasid_t pasid;
> +
> +	dom = iommu_get_domain_for_dev(dev);
> +	if (!dom || !dom->ops || !dom->ops->detach_dev_pasid) {
> +		dev_warn(dev, "No ops for detaching PASID %u", pasid);
> +		return;
> +	}
> +	/* Only support DMA API managed domain type */
> +	if (dom->type == IOMMU_DOMAIN_UNMANAGED ||
> +	    dom->type == IOMMU_DOMAIN_BLOCKED) {
> +		dev_err(dev, "Invalid domain type %d to detach DMA PASID %u\n",
> +			 dom->type, pasid);
> +		return;
> +	}
> +	pasid = dom->pasid;
> +	if (!pasid) {
> +		dev_err(dev, "No DMA PASID attached\n");
> +		return;
> +	}

All WARN_ON's too

> +	dom->ops->detach_dev_pasid(dom, dev, pasid);
> +	if (atomic_dec_and_test(&dom->pasid_users)) {
> +		ioasid_free(pasid);
> +		dom->pasid = 0;
> +	}
> +}
> +EXPORT_SYMBOL(iommu_detach_dma_pasid);
> +
>  /**
>   * iommu_dma_get_resv_regions - Reserved region driver helper
>   * @dev: Device from iommu_get_resv_regions()
> diff --git a/include/linux/dma-iommu.h b/include/linux/dma-iommu.h
> index 24607dc3c2ac..538650b9cb75 100644
> +++ b/include/linux/dma-iommu.h
> @@ -18,6 +18,9 @@ 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);
>  
> +int iommu_attach_dma_pasid(struct device *dev, ioasid_t *pasid);
> +void iommu_detach_dma_pasid(struct device *dev);
> +
>  /* Setup call for arch DMA mapping code */
>  void iommu_setup_dma_ops(struct device *dev, u64 dma_base, u64 dma_limit);
>  int iommu_dma_init_fq(struct iommu_domain *domain);
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index 1164524814cb..281a87fdce77 100644
> +++ b/include/linux/iommu.h
> @@ -105,6 +105,8 @@ struct iommu_domain {
>  	enum iommu_page_response_code (*iopf_handler)(struct iommu_fault *fault,
>  						      void *data);
>  	void *fault_data;
> +	ioasid_t pasid;		/* Used for DMA requests with PASID */
> +	atomic_t pasid_users;

These are poorly named, this is really the DMA API global PASID and
shouldn't be used for other things.

Jason