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

From: David Woodhouse <dwmw2@infradead.org>
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: linux-s390 <linux-s390@vger.kernel.org>,
	Joerg Roedel <jroedel@suse.de>, KVM <kvm@vger.kernel.org>,
	benh@kernel.crashing.org,
	Sebastian Ott <sebott@linux.vnet.ibm.com>,
	linux-kernel@vger.kernel.org,
	virtualization@lists.linux-foundation.org,
	Christian Borntraeger <borntraeger@de.ibm.com>,
	Andy Lutomirski <luto@kernel.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Christoph Hellwig <hch@lst.de>,
	Martin Schwidefsky <schwidefsky@de.ibm.com>
Subject: Re: [PATCH v3 0/3] virtio DMA API core stuff
Date: Wed, 28 Oct 2015 23:13:29 +0900	[thread overview]
Message-ID: <1446041609.3405.228.camel@infradead.org> (raw)
In-Reply-To: <20151028155105-mutt-send-email-mst@redhat.com>

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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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