Message-ID: <1447202682.31884.123.camel@kernel.crashing.org>
Subject: Re: [PATCH v4 0/6] virtio core DMA API conversion
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Andy Lutomirski <luto@amacapital.net>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        David Woodhouse <dwmw2@infradead.org>,
        Martin Schwidefsky <schwidefsky@de.ibm.com>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Sebastian Ott <sebott@linux.vnet.ibm.com>,
        "David S. Miller" <davem@davemloft.net>,
        linux-s390 <linux-s390@vger.kernel.org>,
        Cornelia Huck <cornelia.huck@de.ibm.com>,
        Joerg Roedel <jroedel@suse.de>, KVM <kvm@vger.kernel.org>,
        Christoph Hellwig <hch@lst.de>,
        Linux Virtualization <virtualization@lists.linux-foundation.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        sparclinux@vger.kernel.org
Date: Wed, 11 Nov 2015 11:44:42 +1100
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On Tue, 2015-11-10 at 15:44 -0800, Andy Lutomirski wrote:
> 
> > What about partition <-> partition virtio such as what we could do on
> > PAPR systems. That would have the weak barrier bit.
> >
> 
> Is it partition <-> partition, bypassing IOMMU?

No.

> I think I'd settle for just something that doesn't regress
> non-experimental setups that actually work today and that allow new
> setups (x86 with fixed QEMU and maybe something more complicated on
> powerpc and/or sparc) to work in all cases.
> 
> We could certainly just make powerpc and sparc continue bypassing the
> IOMMU until someone comes up with a way to fix it.  I'll send out some
> patches that do that, and maybe that'll help this make progress.

But we haven't found a solution that works. All we have come up with is
a quirk that will force bypass on virtio always and will not allow us
to operate non-bypassing devices on either of those architectures in
the future.

I'm not too happy about this.

Ben.

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