linux-kernel - Re: [PATCH] vfio iommu type1: Bypass the vma permission check in vfio_pin_pages

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Date:   Mon, 7 Dec 2020 14:48:38 +0000
From:   Stefan Hajnoczi <stefanha@...il.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     Peter Xu <peterx@...hat.com>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        Justin He <Justin.He@....com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] vfio iommu type1: Bypass the vma permission check in
 vfio_pin_pages_remote()

On Thu, Dec 03, 2020 at 05:01:32PM +0100, David Hildenbrand wrote:
> The real question is: do we even *need* DMA from vfio devices to
> virtio-fs regions? If not (do guests rely on it? what does the spec
> state?), just don't care about vfio at all and don't map anything.

Can DMA to/from the virtio-fs DAX Window happen? Yes, the guest could do
it although it's rare.

Is it a great idea to combine VFIO and virtio-fs DAX? Maybe not. It
involves pinning host page cache pages O_o.

Stefan

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