linux-kernel - Re: [PATCH v4 0/6] virtio core DMA API conversion

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Message-ID: <CALCETrVopuN6s7ZTa4ZRe1E1wPiWy_2gMR_OH2B2rK0+VdeWVg@mail.gmail.com>
Date:	Mon, 9 Nov 2015 21:33:07 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	Andy Lutomirski <luto@...nel.org>,
	David Woodhouse <dwmw2@...radead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	sparclinux@...r.kernel.org, Joerg Roedel <jroedel@...e.de>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	Cornelia Huck <cornelia.huck@...ibm.com>,
	Sebastian Ott <sebott@...ux.vnet.ibm.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Christoph Hellwig <hch@....de>, KVM <kvm@...r.kernel.org>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	linux-s390 <linux-s390@...r.kernel.org>,
	Linux Virtualization <virtualization@...ts.linux-foundation.org>,
	"Michael S. Tsirkin" <mst@...hat.com>
Subject: Re: [PATCH v4 0/6] virtio core DMA API conversion

On Mon, Nov 9, 2015 at 9:26 PM, Benjamin Herrenschmidt
<benh@...nel.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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