RE: [PATCH v2 6/8] dmaengine: idxd: Use DMA API for in-kernel DMA with PASID

["Tian, Kevin" <kevin.tian@intel.com>]

> From: Jacob Pan <jacob.jun.pan@linux.intel.com>
> Sent: Tuesday, March 15, 2022 1:07 PM
> 
> The current in-kernel supervisor PASID support is based on the SVM/SVA
> machinery in SVA lib. The binding between a kernel PASID and kernel
> mapping has many flaws. See discussions in the link below.
> 
> This patch enables in-kernel DMA by switching from SVA lib to the
> standard DMA mapping APIs. Since both DMA requests with and without
> PASIDs are mapped identically, there is no change to how DMA APIs are
> used after the kernel PASID is enabled.
> 
> Link: https://lore.kernel.org/linux-
> iommu/20210511194726.GP1002214@nvidia.com/
> Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
> ---
>  drivers/dma/idxd/idxd.h  |  1 -
>  drivers/dma/idxd/init.c  | 34 +++++++++-------------------------
>  drivers/dma/idxd/sysfs.c |  7 -------
>  3 files changed, 9 insertions(+), 33 deletions(-)
> 
> diff --git a/drivers/dma/idxd/idxd.h b/drivers/dma/idxd/idxd.h
> index da72eb15f610..a09ab4a6e1c1 100644
> --- a/drivers/dma/idxd/idxd.h
> +++ b/drivers/dma/idxd/idxd.h
> @@ -276,7 +276,6 @@ struct idxd_device {
>  	struct idxd_wq **wqs;
>  	struct idxd_engine **engines;
> 
> -	struct iommu_sva *sva;
>  	unsigned int pasid;
> 
>  	int num_groups;
> diff --git a/drivers/dma/idxd/init.c b/drivers/dma/idxd/init.c
> index 08a5f4310188..5d1f8dd4abf6 100644
> --- a/drivers/dma/idxd/init.c
> +++ b/drivers/dma/idxd/init.c
> @@ -16,6 +16,7 @@
>  #include <linux/idr.h>
>  #include <linux/intel-svm.h>
>  #include <linux/iommu.h>
> +#include <linux/dma-iommu.h>
>  #include <uapi/linux/idxd.h>
>  #include <linux/dmaengine.h>
>  #include "../dmaengine.h"
> @@ -466,36 +467,22 @@ static struct idxd_device *idxd_alloc(struct pci_dev
> *pdev, struct idxd_driver_d
> 
>  static int idxd_enable_system_pasid(struct idxd_device *idxd)

idxd_enable_pasid_dma() since system pasid is a confusing term now?
Or just remove the idxd specific wrappers and have the caller to call
iommu_enable_pasid_dma() directly given the simple logic here.

>  {
> -	int flags;
> -	unsigned int pasid;
> -	struct iommu_sva *sva;
> +	u32 pasid;
> +	int ret;
> 
> -	flags = SVM_FLAG_SUPERVISOR_MODE;
> -
> -	sva = iommu_sva_bind_device(&idxd->pdev->dev, NULL, &flags);
> -	if (IS_ERR(sva)) {
> -		dev_warn(&idxd->pdev->dev,
> -			 "iommu sva bind failed: %ld\n", PTR_ERR(sva));
> -		return PTR_ERR(sva);
> -	}
> -
> -	pasid = iommu_sva_get_pasid(sva);
> -	if (pasid == IOMMU_PASID_INVALID) {
> -		iommu_sva_unbind_device(sva);
> -		return -ENODEV;
> +	ret = iommu_enable_pasid_dma(&idxd->pdev->dev, &pasid);
> +	if (ret) {
> +		dev_err(&idxd->pdev->dev, "No DMA PASID %d\n", ret);
> +		return ret;
>  	}
> -
> -	idxd->sva = sva;
>  	idxd->pasid = pasid;
> -	dev_dbg(&idxd->pdev->dev, "system pasid: %u\n", pasid);
> +
>  	return 0;
>  }
> 
>  static void idxd_disable_system_pasid(struct idxd_device *idxd)
>  {
> -
> -	iommu_sva_unbind_device(idxd->sva);
> -	idxd->sva = NULL;
> +	iommu_disable_pasid_dma(&idxd->pdev->dev, idxd->pasid);
>  }
> 
>  static int idxd_probe(struct idxd_device *idxd)
> @@ -524,10 +511,7 @@ static int idxd_probe(struct idxd_device *idxd)
>  		} else {
>  			dev_warn(dev, "Unable to turn on SVA feature.\n");
>  		}
> -	} else if (!sva) {
> -		dev_warn(dev, "User forced SVA off via module param.\n");

why removing above 2 lines? they are related to a module param thus
not affected by the logic in this series.

>  	}
> -
>  	idxd_read_caps(idxd);
>  	idxd_read_table_offsets(idxd);
> 
> diff --git a/drivers/dma/idxd/sysfs.c b/drivers/dma/idxd/sysfs.c
> index 7e19ab92b61a..fde6656695ba 100644
> --- a/drivers/dma/idxd/sysfs.c
> +++ b/drivers/dma/idxd/sysfs.c
> @@ -839,13 +839,6 @@ static ssize_t wq_name_store(struct device *dev,
>  	if (strlen(buf) > WQ_NAME_SIZE || strlen(buf) == 0)
>  		return -EINVAL;
> 
> -	/*
> -	 * This is temporarily placed here until we have SVM support for
> -	 * dmaengine.
> -	 */
> -	if (wq->type == IDXD_WQT_KERNEL && device_pasid_enabled(wq-
> >idxd))
> -		return -EOPNOTSUPP;
> -
>  	memset(wq->name, 0, WQ_NAME_SIZE + 1);
>  	strncpy(wq->name, buf, WQ_NAME_SIZE);
>  	strreplace(wq->name, '\n', '\0');
> --
> 2.25.1