linux-kernel - Re: [PATCH v5 00/10] virtio DMA API, yet again

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Date:	Sun, 31 Jan 2016 12:16:18 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Andy Lutomirski <luto@...nel.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	David Woodhouse <dwmw2@...radead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	sparclinux@...r.kernel.org, Joerg Roedel <jroedel@...e.de>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	Cornelia Huck <cornelia.huck@...ibm.com>,
	Sebastian Ott <sebott@...ux.vnet.ibm.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Christoph Hellwig <hch@....de>, KVM <kvm@...r.kernel.org>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	linux-s390 <linux-s390@...r.kernel.org>,
	Linux Virtualization <virtualization@...ts.linux-foundation.org>,
	David Vrabel <david.vrabel@...rix.com>,
	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	"xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>
Subject: Re: [PATCH v5 00/10] virtio DMA API, yet again

On Sun, Jan 31, 2016 at 12:12 PM, Michael S. Tsirkin <mst@...hat.com> wrote:
> On Thu, Jan 28, 2016 at 06:31:13PM -0800, Andy Lutomirski wrote:
>> This switches virtio to use the DMA API on Xen and if requested by
>> module option.
>>
>> This fixes virtio on Xen, and it should break anything because it's
>> off by default on everything except Xen PV on x86.
>>
>> To the Xen people: is this okay?  If it doesn't work on other Xen
>> variants (PVH? HVM?), can you submit follow-up patches to fix it?
>>
>> To everyone else: we've waffled on this for way too long.  I think
>> we should to get DMA API implementation in with a conservative
>> policy like this rather than waiting until we achieve perfection.
>> I'm tired of carrying these patches around.
>
> I agree, thanks for working on this!
>
>> Michael, if these survive review, can you stage these in your tree?
>
> Yes, I'll stage everything except 10/10. I'd rather not maintain a
> module option like this, things work for now and I'm working on a
> clean solution for things like dpdk within guest.

The module option was mainly for testing, but patching in a "return
true" works just as well.

I ran the code through the DMA API debugging stuff and swiotlb=force
with the module option set under KVM (no Xen), and everything seemed
to work.

--Andy