linux-kernel - RE: [RFC] /dev/ioasid uAPI proposal

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Date:   Fri, 4 Jun 2021 09:19:50 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Alex Williamson <alex.williamson@...hat.com>,
        Jason Gunthorpe <jgg@...dia.com>
CC:     Jean-Philippe Brucker <jean-philippe@...aro.org>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        Jonathan Corbet <corbet@....net>,
        Robin Murphy <robin.murphy@....com>,
        LKML <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        David Gibson <david@...son.dropbear.id.au>,
        Kirti Wankhede <kwankhede@...dia.com>,
        "David Woodhouse" <dwmw2@...radead.org>,
        Jason Wang <jasowang@...hat.com>
Subject: RE: [RFC] /dev/ioasid uAPI proposal

> From: Alex Williamson <alex.williamson@...hat.com>
> Sent: Friday, June 4, 2021 4:42 AM
> 
> > 'qemu --allow-no-snoop' makes more sense to me
> 
> I'd be tempted to attach it to the -device vfio-pci option, it's
> specific drivers for specific devices that are going to want this and
> those devices may not be permanently attached to the VM.  But I see in
> the other thread you're trying to optimize IOMMU page table sharing.
> 
> There's a usability question in either case though and I'm not sure how
> to get around it other than QEMU or the kernel knowing a list of
> devices (explicit IDs or vendor+class) to select per device defaults.
> 

"-device vfio-pci" is a per-device option, which implies that the
no-snoop choice is given to the admin then no need to maintain 
a fixed device list in Qemu?

Thanks
Kevin