linux-kernel - Re: [PATCH v7 17/22] vfio-pci/zdev: add open/close device hooks

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Message-ID: <305208c4-db8a-5751-2ffc-753751a70815@linux.ibm.com>
Date:   Mon, 16 May 2022 17:59:01 -0400
From:   Matthew Rosato <mjrosato@...ux.ibm.com>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     alex.williamson@...hat.com, linux-s390@...r.kernel.org,
        cohuck@...hat.com, schnelle@...ux.ibm.com, farman@...ux.ibm.com,
        pmorel@...ux.ibm.com, borntraeger@...ux.ibm.com, hca@...ux.ibm.com,
        gor@...ux.ibm.com, gerald.schaefer@...ux.ibm.com,
        agordeev@...ux.ibm.com, svens@...ux.ibm.com, frankja@...ux.ibm.com,
        david@...hat.com, imbrenda@...ux.ibm.com, vneethv@...ux.ibm.com,
        oberpar@...ux.ibm.com, freude@...ux.ibm.com, thuth@...hat.com,
        pasic@...ux.ibm.com, pbonzini@...hat.com, corbet@....net,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org
Subject: Re: [PATCH v7 17/22] vfio-pci/zdev: add open/close device hooks

On 5/16/22 2:35 PM, Jason Gunthorpe wrote:
> On Mon, May 16, 2022 at 02:30:46PM -0400, Matthew Rosato wrote:
> 
>> Conceptually I think this would work for QEMU anyway (it always sets the kvm
>> before we open the device).  I tried to test the idea quickly but couldn't
>> get the following to apply on vfio-next or your vfio_group_locking -- but I
>> understand what you're trying to do so I'll re-work and try it out.
> 
> I created it on 8c9350e9bf43de1ebab3cc8a80703671e6495ab4 which is the
> vfio_group_locking.. I can send you a github if it helps
> https://github.com/jgunthorpe/linux/commits/vfio_group_lockin
> 
Thanks -- I was able to successfully test your proposed idea (+ some 
changes to make it compile :)) on top of vfio_group_locking along with a 
modified version of my zdev series.  I also tried it out with vfio-ap 
successfully, but have nothing to test GVT with.

That said, this has caused me to realize that 'iommu: 
iommu_group_claim_dma_owner() must always assign a domain' breaks s390x 
vfio-pci :( I wonder if it is due to the way s390x PCI currently 
switches between dma ops and iommu ops.  It looks like it breaks vfio-ap 
mdevs too, but I know less about that --  I will have to investigate 
both more tomorrow.