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

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Date:	Wed, 28 Oct 2015 23:13:29 +0900
From:	David Woodhouse <dwmw2@...radead.org>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Christian Borntraeger <borntraeger@...ibm.com>,
	Andy Lutomirski <luto@...nel.org>,
	linux-kernel@...r.kernel.org, Joerg Roedel <jroedel@...e.de>,
	Cornelia Huck <cornelia.huck@...ibm.com>,
	Sebastian Ott <sebott@...ux.vnet.ibm.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Christoph Hellwig <hch@....de>, benh@...nel.crashing.org,
	KVM <kvm@...r.kernel.org>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	linux-s390 <linux-s390@...r.kernel.org>,
	virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v3 0/3] virtio DMA API core stuff

On Wed, 2015-10-28 at 16:05 +0200, Michael S. Tsirkin wrote:
> 
> Short answer - platforms need a way to discover, and express different
> security requirements of different devices.

Sure. PLATFORMS need that. Do not let it go anywhere near your device
drivers. Including the virtio drivers.

> If they continue to lack that, we'll need a custom API in virtio,
> and while this seems a bit less elegant, I would not see that as
> the end of the world at all, there are not that many virtio drivers.

No. If they continue to lack that, we fix them. This is a *platform*
issue. The DMA API shall do the right thing. Do not second-guess it.


 (From the other mail)
> > > OK so I guess that means we should prefer a transport-specific
> > > interface in virtio-pci then.
> >
> > Why?
> 
> Because you said you are doing something device tree specific for 
> ARM, aren't you?

Nonono. The ARM platform code might do that, and the DMA API on ARM
*might* give you I/O virtual addresses that look a lot like the
physical addresses you asked it to map. That's none of your business.
Drivers use DMA API. No more talky.

-- 
dwmw2



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