Re: [PATCH v4 0/4] virtio: Clean up scatterlists and use the DMA API

From: Jan Kiszka <jan.kiszka@siemens.com>
To: Paolo Bonzini <pbonzini@redhat.com>,
	Andy Lutomirski <luto@amacapital.net>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: "linux-s390@vger.kernel.org" <linux-s390@vger.kernel.org>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	Stefan Hajnoczi <stefanha@gmail.com>,
	Rusty Russell <rusty@rustcorp.com.au>,
	xen-devel <Xen-devel@lists.xen.org>,
	Christian Borntraeger <borntraeger@de.ibm.com>,
	Cornelia Huck <cornelia.huck@de.ibm.com>,
	"linux390@de.ibm.com" <linux390@de.ibm.com>,
	Linux Virtualization <virtualization@lists.linux-foundation.org>
Subject: Re: [PATCH v4 0/4] virtio: Clean up scatterlists and use the DMA API
Date: Wed, 29 Jul 2015 10:20:34 +0200	[thread overview]
Message-ID: <55B88CD2.4040605__12087.8556780101$1438158128$gmane$org@siemens.com> (raw)
In-Reply-To: <55B88C0E.9050104@redhat.com>

On 2015-07-29 10:17, Paolo Bonzini wrote:
> 
> 
> On 29/07/2015 02:47, Andy Lutomirski wrote:
>>>> If new kernels ignore the IOMMU for devices that don't set the flag
>>>> and there are physical devices that already exist and don't set the
>>>> flag, then those devices won't work reliably on most modern
>>>> non-virtual platforms, PPC included.
>>>
>>> Are there many virtio physical devices out there ? We are talking about
>>> a virtio flag right ? Or have you been considering something else ?
>>
>> Yes, virtio flag.  I dislike having a virtio flag at all, but so far
>> no one has come up with any better ideas.  If there was a reliable,
>> cross-platform mechanism for per-device PCI bus properties, I'd be all
>> for using that instead.
> 
> No, a virtio flag doesn't make sense.

That will create the risk of subtly breaking old guests over new setups.
I wouldn't suggest this.

Jan

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