netdev - Re: [PATCH v2] vhost/vdpa: Add MSI translation tables to iommu for software-managed MSI

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Date:   Mon, 20 Feb 2023 10:24:22 -0500
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     Jason Gunthorpe <jgg@...dia.com>,
        Nanyong Sun <sunnanyong@...wei.com>, joro@...tes.org,
        will@...nel.org, robin.murphy@....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 v2] vhost/vdpa: Add MSI translation tables to iommu for
 software-managed MSI

On Mon, Feb 20, 2023 at 10:36:27AM +0800, Jason Wang wrote:
> On Fri, Feb 17, 2023 at 6:11 PM Michael S. Tsirkin <mst@...hat.com> wrote:
> >
> > On Fri, Feb 17, 2023 at 01:35:59PM +0800, Jason Wang wrote:
> > > On Fri, Feb 17, 2023 at 8:15 AM Jason Gunthorpe <jgg@...dia.com> wrote:
> > > >
> > > > On Tue, Feb 07, 2023 at 08:08:43PM +0800, Nanyong Sun 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.
> > > >
> > > > 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..
> > >
> > > Yes, but we probably need a patch for -stable.
> >
> > Hmm do we? this looks like it's enabling new platforms is not a bugfix...
> 
> I think we haven't limited vDPA to any specific arch in the past?
> 
> Thanks

No, but it still fails gracefully right?

Anyway, this will need iommu maintainer's ack.  We'll see.


> >
> > > >
> > > > Also the iommu_group_has_isolated_msi() check is missing on the vdpa
> > > > path, and it is missing the iommu ownership mechanism.
> > >
> > > Ok.
> > >
> > > >
> > > > Also which in-tree VDPA driver that uses the iommu runs on ARM? Please
> > >
> > > ifcvf and vp_vpda are two drivers that use platform IOMMU.
> > >
> > > Thanks
> > >
> > > > don't propose core changes for unmerged drivers. :(
> > > >
> > > > Jason
> > > >
> >