From mboxrd@z Thu Jan  1 00:00:00 1970
From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Subject: Re: [PATCH v4 0/4] virtio: Clean up scatterlists and use the DMA API
Date: Tue, 2 Sep 2014 16:56:26 -0400
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To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: "linux-s390@vger.kernel.org" <linux-s390@vger.kernel.org>, "Michael S. Tsirkin" <mst@redhat.com>, Andy Lutomirski <luto@amacapital.net>, Christian Borntraeger <borntraeger@de.ibm.com>, Paolo Bonzini <pbonzini@redhat.com>, "linux390@de.ibm.com" <linux390@de.ibm.com>, Linux Virtualization <virtualization@lists.linux-foundation.org>
List-ID: <linux-s390.vger.kernel.org>

On Wed, Sep 03, 2014 at 06:53:33AM +1000, Benjamin Herrenschmidt wrote:
> On Mon, 2014-09-01 at 22:55 -0700, Andy Lutomirski wrote:
> > 
> > On x86, at least, I doubt that we'll ever see a physically addressed
> > PCI virtio device for which ACPI advertises an IOMMU, since any sane
> > hypervisor will just not advertise an IOMMU for the virtio device.
> > But are there arm64 or PPC guests that use virtio_pci, that have
> > IOMMUs, and that will malfunction if the virtio_pci driver ends up
> > using the IOMMU?  I certainly hope not, since these systems might be
> > very hard-pressed to work right if someone plugged in a physical
> > virtio-speaking PCI device.
> 
> It will definitely not work on ppc64. We always have IOMMUs on pseries,
> all PCI busses do, and because it's a paravirtualized environment,
> napping/unmapping pages means hypercalls -> expensive.
> 
> But our virtio implementation bypasses it in qemu, so if virtio-pci
> starts using the DMA mapping API without changing the DMA ops under the
> hood, it will break for us.

What is the default dma_ops that the Linux guests start with as
guests under ppc64?

Thanks!
> 
> Cheers,
> Ben.
> 
>