netdev - Re: [PATCH] vhost/vdpa: Add MSI translation tables to iommu for software-managed MSI

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Date:   Sun, 29 Jan 2023 14:02:08 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Nanyong Sun <sunnanyong@...wei.com>
Cc:     joro@...tes.org, will@...nel.org, robin.murphy@....com,
        mst@...hat.com, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        wangrong68@...wei.com
Subject: Re: [PATCH] vhost/vdpa: Add MSI translation tables to iommu for
 software-managed MSI

On Sat, Jan 28, 2023 at 10:25 AM Nanyong Sun <sunnanyong@...wei.com> wrote:
>
> From: Rong Wang <wangrong68@...wei.com>
>
> Once enable iommu domain for one device, the MSI
> translation tables have to be there for software-managed MSI.
> Otherwise, platform with software-managed MSI without an
> irq bypass function, can not get a correct memory write event
> from pcie, will not get irqs.
> The solution is to obtain the MSI phy base address from
> iommu reserved region, and set it to iommu MSI cookie,
> then translation tables will be created while request irq.
>
> Signed-off-by: Rong Wang <wangrong68@...wei.com>
> Signed-off-by: Nanyong Sun <sunnanyong@...wei.com>
> ---
>  drivers/iommu/iommu.c |  1 +
>  drivers/vhost/vdpa.c  | 53 ++++++++++++++++++++++++++++++++++++++++---
>  2 files changed, 51 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index de91dd88705b..f6c65d5d8e2b 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -2623,6 +2623,7 @@ void iommu_get_resv_regions(struct device *dev, struct list_head *list)
>         if (ops->get_resv_regions)
>                 ops->get_resv_regions(dev, list);
>  }
> +EXPORT_SYMBOL_GPL(iommu_get_resv_regions);
>
>  /**
>   * iommu_put_resv_regions - release resered regions
> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> index ec32f785dfde..31d3e9ed4cfa 100644
> --- a/drivers/vhost/vdpa.c
> +++ b/drivers/vhost/vdpa.c
> @@ -1103,6 +1103,48 @@ static ssize_t vhost_vdpa_chr_write_iter(struct kiocb *iocb,
>         return vhost_chr_write_iter(dev, from);
>  }
>
> +static bool vhost_vdpa_check_sw_msi(struct list_head *dev_resv_regions, phys_addr_t *base)
> +{
> +       struct iommu_resv_region *region;
> +       bool ret = false;
> +
> +       list_for_each_entry(region, dev_resv_regions, list) {
> +               /*
> +                * The presence of any 'real' MSI regions should take
> +                * precedence over the software-managed one if the
> +                * IOMMU driver happens to advertise both types.
> +                */
> +               if (region->type == IOMMU_RESV_MSI) {
> +                       ret = false;
> +                       break;
> +               }
> +
> +               if (region->type == IOMMU_RESV_SW_MSI) {
> +                       *base = region->start;
> +                       ret = true;
> +               }
> +       }
> +
> +       return ret;
> +}

Can we unify this with what VFIO had?

> +
> +static int vhost_vdpa_get_msi_cookie(struct iommu_domain *domain, struct device *dma_dev)
> +{
> +       struct list_head dev_resv_regions;
> +       phys_addr_t resv_msi_base = 0;
> +       int ret = 0;
> +
> +       INIT_LIST_HEAD(&dev_resv_regions);
> +       iommu_get_resv_regions(dma_dev, &dev_resv_regions);
> +
> +       if (vhost_vdpa_check_sw_msi(&dev_resv_regions, &resv_msi_base))
> +               ret = iommu_get_msi_cookie(domain, resv_msi_base);
> +
> +       iommu_put_resv_regions(dma_dev, &dev_resv_regions);
> +
> +       return ret;
> +}
> +
>  static int vhost_vdpa_alloc_domain(struct vhost_vdpa *v)
>  {
>         struct vdpa_device *vdpa = v->vdpa;
> @@ -1128,11 +1170,16 @@ static int vhost_vdpa_alloc_domain(struct vhost_vdpa *v)
>
>         ret = iommu_attach_device(v->domain, dma_dev);
>         if (ret)
> -               goto err_attach;
> +               goto err_alloc_domain;
>
> -       return 0;
> +       ret = vhost_vdpa_get_msi_cookie(v->domain, dma_dev);

Do we need to check the overlap mapping and record it in the interval
tree (as what VFIO did)?

Thanks

> +       if (ret)
> +               goto err_attach_device;
>
> -err_attach:
> +       return 0;
> +err_attach_device:
> +       iommu_detach_device(v->domain, dma_dev);
> +err_alloc_domain:
>         iommu_domain_free(v->domain);
>         return ret;
>  }
> --
> 2.25.1
>