linux-kernel - Re: [dpdk-dev] [PATCH] vfio: Include No-IOMMU mode

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Date:	Wed, 02 Dec 2015 17:19:18 +0100
From:	Thomas Monjalon <thomas.monjalon@...nd.com>
To:	Alex Williamson <alex.williamson@...hat.com>
Cc:	dev@...k.org, Avi Kivity <avi@...lladb.com>, gleb@...lladb.com,
	mst@...hat.com, corbet@....net, linux-kernel@...r.kernel.org,
	iommu@...ts.linux-foundation.org, hjk@...sjkoch.de,
	gregkh@...uxfoundation.org
Subject: Re: [dpdk-dev] [PATCH] vfio: Include No-IOMMU mode

Hi,

2015-12-02 08:28, Alex Williamson:
> On Mon, 2015-11-16 at 19:12 +0200, Avi Kivity wrote:
> > On 11/16/2015 07:06 PM, Alex Williamson wrote:
> > > FYI, this is now in v4.4-rc1 (the slightly modified v2 version).  I want
> > > to give fair warning though that while we seem to agree on this idea, it
> > > hasn't been proven with a userspace driver port.  I've opted to include
> > > it in this merge window rather than delaying it until v4.5, but I really
> > > need to see a user for this before the end of the v4.4 cycle or I think
> > > we'll need to revert and revisit for v4.5 anyway.  I don't really have
> > > any interest in adding and maintaining code that has no users.  Please
> > > keep me informed of progress with a dpdk port.  Thanks,
> > 
> > Thanks Alex.  Copying the dpdk mailing list, where the users live.
> > 
> > dpdk-ers: vfio-noiommu is a replacement for uio_pci_generic and 
> > uio_igb.  It supports MSI-X and so can be used on SR/IOV VF devices.  
> > The intent is that you can use dpdk without an external module, using 
> > vfio, whether you are on bare metal with an iommu, bare metal without an 
> > iommu, or virtualized.  However, dpdk needs modification to support this.
> 
> Still no users for this that I'm aware of.  I'm going to revert this in
> rc5 unless something changes.  Thanks,

Removing needs for out-of-tree modules is a really nice achievement.
Yes, we (in the DPDK project) should check how to use this no-iommu VFIO
and to replace igb_uio.

I'm sorry we failed to catch your email and follow up.
Is it really too late? What is the risk of keeping it in Linux 4.4?
Advertising a new feature and removing it would be frustrating.

Have you tried this VFIO mode with DPDK?
How complex would be the patch to support it?

Thanks
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