From: Andy Lutomirski <luto@amacapital.net>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
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
Subject: Re: [PATCH v4 0/6] virtio core DMA API conversion
Date: Tue, 10 Nov 2015 10:54:37 -0800 [thread overview]
Message-ID: <CALCETrVkE3=KCxK-_bf-P8UfTS96Vck+QPE8EsLvP7THxpLe1A@mail.gmail.com> (raw)
In-Reply-To: <1447151874.31884.82.camel@kernel.crashing.org>
On Nov 10, 2015 2:38 AM, "Benjamin Herrenschmidt"
<benh@kernel.crashing.org> wrote:
>
> On Mon, 2015-11-09 at 21:35 -0800, Andy Lutomirski wrote:
> >
> > We could do it the other way around: on powerpc, if a PCI device is in
> > that range and doesn't have the "bypass" property at all, then it's
> > assumed to bypass the IOMMU. This means that everything that
> > currently works continues working. If someone builds a physical
> > virtio device or uses another system in PCIe target mode speaking
> > virtio, then it won't work until they upgrade their firmware to set
> > bypass=0. Meanwhile everyone using hypothetical new QEMU also gets
> > bypass=0 and no ambiguity.
> >
> > vfio will presumably notice the bypass and correctly refuse to map any
> > current virtio devices.
> >
> > Would that work?
>
> That would be extremely strange from a platform perspective. Any device
> in that vendor/device range would bypass the iommu unless some new
> property "actually-works-like-a-real-pci-device" happens to exist in
> the device-tree, which we would then need to define somewhere and
> handle accross at least 3 different platforms who get their device-tree
> from widly different places.
>
> Also if tomorrow I create a PCI device that implements virtio-net and
> put it in a machine running IBM proprietary firmware (or Apple's or
> Sun's), it won't have that property...
>
> This is not hypothetical. People are using virtio to do point-to-point
> communication between machines via PCIe today.
Does that work on powerpc on existing kernels?
Anyway, here's another crazy idea: make the quirk assume that the
IOMMU is bypasses if and only if the weak barriers bit is set on
systems that are missing the new DT binding.
--Andy
>
> Cheers,
> Ben.
>
>
next prev parent reply other threads:[~2015-11-10 18:55 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-30 1:09 [PATCH v4 0/6] virtio core DMA API conversion Andy Lutomirski
2015-10-30 1:09 ` [PATCH v4 1/6] virtio-net: Stop doing DMA from the stack Andy Lutomirski
2015-10-30 13:55 ` Christian Borntraeger
2015-10-31 5:02 ` Andy Lutomirski
2015-10-30 1:09 ` [PATCH v4 2/6] virtio_ring: Support DMA APIs Andy Lutomirski
2015-10-30 12:01 ` Cornelia Huck
2015-10-30 12:05 ` Christian Borntraeger
2015-10-30 18:51 ` Andy Lutomirski
2015-10-30 1:09 ` [PATCH v4 3/6] virtio_pci: Use the DMA API Andy Lutomirski
2015-10-30 1:09 ` [PATCH v4 4/6] virtio: Add improved queue allocation API Andy Lutomirski
2015-10-30 1:09 ` [PATCH v4 5/6] virtio_mmio: Use the DMA API Andy Lutomirski
2015-10-30 1:09 ` [PATCH v4 6/6] virtio_pci: " Andy Lutomirski
2015-10-30 1:17 ` [PATCH v4 0/6] virtio core DMA API conversion Andy Lutomirski
2015-10-30 9:57 ` Christian Borntraeger
2015-11-09 12:15 ` Michael S. Tsirkin
2015-11-09 12:27 ` Paolo Bonzini
2015-11-09 22:58 ` Benjamin Herrenschmidt
2015-11-10 0:46 ` Andy Lutomirski
2015-11-10 2:04 ` Benjamin Herrenschmidt
2015-11-10 2:18 ` Andy Lutomirski
2015-11-10 5:26 ` Benjamin Herrenschmidt
2015-11-10 5:33 ` Andy Lutomirski
2015-11-10 5:28 ` Benjamin Herrenschmidt
2015-11-10 5:35 ` Andy Lutomirski
2015-11-10 10:37 ` Benjamin Herrenschmidt
2015-11-10 12:43 ` Michael S. Tsirkin
2015-11-10 19:37 ` Benjamin Herrenschmidt
2015-11-10 18:54 ` Andy Lutomirski [this message]
2015-11-10 22:27 ` Benjamin Herrenschmidt
2015-11-10 23:44 ` Andy Lutomirski
2015-11-11 0:44 ` Benjamin Herrenschmidt
2015-11-11 4:46 ` Andy Lutomirski
2015-11-11 5:08 ` Benjamin Herrenschmidt
2015-11-10 7:28 ` Jan Kiszka
2015-11-10 9:45 ` Knut Omang
2015-11-10 10:26 ` Benjamin Herrenschmidt
2015-11-10 10:27 ` Joerg Roedel
2015-11-10 19:36 ` Benjamin Herrenschmidt
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