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

Tian, Kevin
2022-03-18T06:10:57Z

> 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