Date:   Fri, 17 Feb 2023 08:43:31 -0400
From:   Jason Gunthorpe <jgg@nvidia.com>
To:     "Michael S. Tsirkin" <mst@redhat.com>
Cc:     Nanyong Sun <sunnanyong@huawei.com>, joro@8bytes.org,
        will@kernel.org, robin.murphy@arm.com, jasowang@redhat.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
Subject: Re: [PATCH v2] vhost/vdpa: Add MSI translation tables to iommu for
 software-managed MSI
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On Fri, Feb 17, 2023 at 05:12:29AM -0500, Michael S. Tsirkin wrote:
> On Thu, Feb 16, 2023 at 08:14:50PM -0400, Jason Gunthorpe wrote:
> > On Tue, Feb 07, 2023 at 08:08:43PM +0800, Nanyong Sun wrote:
> > > From: Rong Wang <wangrong68@huawei.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.
> > 
> > Probably not what anyone wants to hear, but I would prefer we not add
> > more uses of this stuff. It looks like we have to get rid of
> > iommu_get_msi_cookie() :\
> > 
> > I'd like it if vdpa could move to iommufd not keep copying stuff from
> > it..
> 
> Absolutely but when is that happening?

Don't know, I think it has to come from the VDPA maintainers, Nicolin
made some drafts but wasn't able to get it beyond that.

Please have people who need more iommu platform enablement to pick it
up instead of merging hacks like this..

We are very close to having nested translation on ARM so anyone who is
serious about VDPA on ARM is going to need iommufd anyhow.

Jason