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From: Andy Lutomirski <luto@amacapital.net>
Date: Mon, 9 Nov 2015 21:33:07 -0800
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Subject: Re: [PATCH v4 0/6] virtio core DMA API conversion
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Andy Lutomirski <luto@kernel.org>, David Woodhouse <dwmw2@infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "David S. Miller" <davem@davemloft.net>, sparclinux@vger.kernel.org,
        Joerg Roedel <jroedel@suse.de>,
        Christian Borntraeger <borntraeger@de.ibm.com>,
        Cornelia Huck <cornelia.huck@de.ibm.com>,
        Sebastian Ott <sebott@linux.vnet.ibm.com>,
        Paolo Bonzini <pbonzini@redhat.com>, Christoph Hellwig <hch@lst.de>,
        KVM <kvm@vger.kernel.org>, Martin Schwidefsky <schwidefsky@de.ibm.com>,
        linux-s390 <linux-s390@vger.kernel.org>,
        Linux Virtualization <virtualization@lists.linux-foundation.org>,
        "Michael S. Tsirkin" <mst@redhat.com>
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On Mon, Nov 9, 2015 at 9:26 PM, Benjamin Herrenschmidt
<benh@kernel.crashing.org> wrote:
> On Mon, 2015-11-09 at 18:18 -0800, Andy Lutomirski wrote:
>>
>> Which leaves the special case of Xen, where even preexisting devices
>> don't bypass the IOMMU.  Can we keep this specific to powerpc and
>> sparc?  On x86, this problem is basically nonexistent, since the IOMMU
>> is properly self-describing.
>>
>> IOW, I think that on x86 we should assume that all virtio devices
>> honor the IOMMU.
>
> You don't like performances ? :-)

This should have basically no effect.  Every non-experimental x86
virtio setup in existence either doesn't work at all (Xen) or has DMA
ops that are no-ops.

--Andy
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