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

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Date:   Thu, 16 Feb 2023 20:14:50 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Nanyong Sun <sunnanyong@...wei.com>
Cc:     joro@...tes.org, will@...nel.org, robin.murphy@....com,
        mst@...hat.com, jasowang@...hat.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 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..

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