linux-kernel - Re: [PATCH v3 0/3] virtio DMA API core stuff

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Date:	Thu, 19 Nov 2015 13:59:05 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Sebastian Ott <sebott@...ux.vnet.ibm.com>,
	linux-s390 <linux-s390@...r.kernel.org>,
	Cornelia Huck <cornelia.huck@...ibm.com>,
	Joerg Roedel <jroedel@...e.de>,
	Linux Virtualization <virtualization@...ts.linux-foundation.org>,
	Christoph Hellwig <hch@....de>,
	David Woodhouse <dwmw2@...radead.org>,
	KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH v3 0/3] virtio DMA API core stuff

On Nov 19, 2015 5:45 AM, "Michael S. Tsirkin" <mst@...hat.com> wrote:
>
> On Tue, Oct 27, 2015 at 11:38:57PM -0700, Andy Lutomirski wrote:
> > This switches virtio to use the DMA API unconditionally.  I'm sure
> > it breaks things, but it seems to work on x86 using virtio-pci, with
> > and without Xen, and using both the modern 1.0 variant and the
> > legacy variant.
>
> So thinking hard about it, I don't see any real drawbacks to making this
> conditional on a new feature bit, that Xen can then set..

Can you elaborate?  If I run QEMU, hosting Xen, hosting Linux, and the
virtio device is provided by QEMU, then how does Xen set the bit?
Similarly, how would Xen set the bit for a real physical device?


--Andy
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