Date:   Fri, 17 Feb 2023 05:12:29 -0500
From:   "Michael S. Tsirkin" <mst@redhat.com>
To:     Jason Gunthorpe <jgg@nvidia.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
Message-ID: <20230217051158-mutt-send-email-mst@kernel.org>
References: <20230207120843.1580403-1-sunnanyong@huawei.com>
 <Y+7G+tiBCjKYnxcZ@nvidia.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <Y+7G+tiBCjKYnxcZ@nvidia.com>
Precedence: bulk

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?

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