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Date:   Thu, 23 Mar 2023 09:20:44 -0300
From:   Jason Gunthorpe <jgg@nvidia.com>
To:     Nanyong Sun <sunnanyong@huawei.com>
Cc:     "Michael S. Tsirkin" <mst@redhat.com>,
        Jason Wang <jasowang@redhat.com>, joro@8bytes.org,
        will@kernel.org, robin.murphy@arm.com, iommu@lists.linux.dev,
        linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        virtualization@lists.linux-foundation.org, netdev@vger.kernel.org,
        wangrong68@huawei.com, Cindy Lu <lulu@redhat.com>
Subject: Re: [PATCH v2] vhost/vdpa: Add MSI translation tables to iommu for
 software-managed MSI
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On Thu, Mar 23, 2023 at 08:15:44PM +0800, Nanyong Sun wrote:
> On 2023/3/23 19:31, Jason Gunthorpe wrote:
> 
> > On Thu, Mar 23, 2023 at 05:22:36PM +0800, Nanyong Sun wrote:
> > > > A patch to export that function is alread posted:
> > > > 
> > > > https://lore.kernel.org/linux-iommu/BN9PR11MB52760E9705F2985EACCD5C4A8CBA9@BN9PR11MB5276.namprd11.prod.outlook.com/T/#u
> > > > 
> > > > But I do not want VDPA to mis-use it unless it also implements all the
> > > > ownership stuff properly.
> > > > 
> > > I want to confirm if we need to introduce iommu group logic to vdpa, as "all
> > > the ownership stuff" ?
> > You have to call iommu_device_claim_dma_owner()
> > 
> > But again, this is all pointless, iommufd takes are of all of this and
> > VDPA should switch to it instead of more hacking.
> > 
> > Jason
> > .
> Yeah,  thanks for your suggestion，but as Michael and Jason Wang said,
> before iommufd is ready, we may need to make vDPA work well on software
> managed MSI platforms.
> To achieve that, basically we have two ways:
> 
> 1. export iommu_get_resv_regions, and get regions device by device.
> 2. introduce iommu group, get regions by iommu_get_group_resv_regions, which
> already exported.

I do not think you should dig the hole deeper. If proper iommu
support is important to you then you should invest in iommufd
conversion.

Jason