netdev - Re: [PATCH v3] vhost/vdpa: Add MSI translation tables to iommu for software-managed MSI

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Message-ID: <20240329051334-mutt-send-email-mst@kernel.org>
Date: Fri, 29 Mar 2024 05:13:44 -0400
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Jason Wang <jasowang@...hat.com>
Cc: Wang Rong <w_angrong@....com>, kvm@...r.kernel.org,
	virtualization@...ts.linux.dev, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, Cindy Lu <lulu@...hat.com>
Subject: Re: [PATCH v3] vhost/vdpa: Add MSI translation tables to iommu for
 software-managed MSI

On Fri, Mar 29, 2024 at 11:55:50AM +0800, Jason Wang wrote:
> On Wed, Mar 27, 2024 at 5:08 PM Jason Wang <jasowang@...hat.com> wrote:
> >
> > On Thu, Mar 21, 2024 at 3:00 PM Michael S. Tsirkin <mst@...hat.com> wrote:
> > >
> > > On Wed, Mar 20, 2024 at 06:19:12PM +0800, Wang Rong wrote:
> > > > From: Rong Wang <w_angrong@....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.
> > > >
> > > > Change log
> > > > ----------
> > > >
> > > > v1->v2:
> > > > - add resv iotlb to avoid overlap mapping.
> > > > v2->v3:
> > > > - there is no need to export the iommu symbol anymore.
> > > >
> > > > Signed-off-by: Rong Wang <w_angrong@....com>
> > >
> > > There's in interest to keep extending vhost iotlb -
> > > we should just switch over to iommufd which supports
> > > this already.
> >
> > IOMMUFD is good but VFIO supports this before IOMMUFD. This patch
> > makes vDPA run without a backporting of full IOMMUFD in the production
> > environment. I think it's worth.
> >
> > If you worry about the extension, we can just use the vhost iotlb
> > existing facility to do this.
> >
> > Thanks
> 
> Btw, Wang Rong,
> 
> It looks that Cindy does have the bandwidth in working for IOMMUFD support.

I think you mean she does not.

> Do you have the will to do that?
> 
> Thanks