From: "Michael S. Tsirkin" <mst@redhat.com>
To: Will Deacon <will.deacon@arm.com>
Cc: Robin Murphy <robin.murphy@arm.com>,
linux-arm-kernel@lists.infradead.org, luto@kernel.org,
virtualization@lists.linux-foundation.org
Subject: Re: [PATCH v2 2/2] vring: Force use of DMA API for ARM-based systems
Date: Fri, 13 Jan 2017 00:12:56 +0200 [thread overview]
Message-ID: <20170112232931-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <20170111100139.GC12388@arm.com>
On Wed, Jan 11, 2017 at 10:01:39AM +0000, Will Deacon wrote:
> On Wed, Jan 11, 2017 at 01:33:31AM +0200, Michael S. Tsirkin wrote:
> > On Tue, Jan 10, 2017 at 05:51:18PM +0000, Robin Murphy wrote:
> > > From: Will Deacon <will.deacon@arm.com>
> > >
> > > Booting Linux on an ARM fastmodel containing an SMMU emulation results
> > > in an unexpected I/O page fault from the legacy virtio-blk PCI device:
> > >
> > > [ 1.211721] arm-smmu-v3 2b400000.smmu: event 0x10 received:
> > > [ 1.211800] arm-smmu-v3 2b400000.smmu: 0x00000000fffff010
> > > [ 1.211880] arm-smmu-v3 2b400000.smmu: 0x0000020800000000
> > > [ 1.211959] arm-smmu-v3 2b400000.smmu: 0x00000008fa081002
> > > [ 1.212075] arm-smmu-v3 2b400000.smmu: 0x0000000000000000
> > > [ 1.212155] arm-smmu-v3 2b400000.smmu: event 0x10 received:
> > > [ 1.212234] arm-smmu-v3 2b400000.smmu: 0x00000000fffff010
> > > [ 1.212314] arm-smmu-v3 2b400000.smmu: 0x0000020800000000
> > > [ 1.212394] arm-smmu-v3 2b400000.smmu: 0x00000008fa081000
> > > [ 1.212471] arm-smmu-v3 2b400000.smmu: 0x0000000000000000
> > >
> > > <system hangs failing to read partition table>
> > >
> > > This is because the virtio-blk is behind an SMMU, so we have consequently
> > > swizzled its DMA ops and configured the SMMU to translate accesses. This
> > > then requires the vring code to use the DMA API to establish translations,
> > > otherwise all transactions will result in fatal faults and termination.
> > >
> > > Given that ARM-based systems only see an SMMU if one is really present
> > > (the topology is all described by firmware tables such as device-tree or
> > > IORT), then we can safely use the DMA API for all virtio devices.
> > >
> > > Cc: Andy Lutomirski <luto@kernel.org>
> > > Cc: Michael S. Tsirkin <mst@redhat.com>
> > > Signed-off-by: Will Deacon <will.deacon@arm.com>
> >
> > I'd like to better understand then need for this one.
> > Can't the device in question just set VIRTIO_F_IOMMU_PLATFORM ?
> >
> > I'd rather we avoided need for more hacks and just
> > have everyone switch to that.
>
> There are a couple of problems with VIRTIO_F_IOMMU_PLATFORM:
>
> 1. It doesn't exist for legacy devices, which are all we have on the
> platform in question.
>
> 2. It's not documented in the virtio sp^H^HSTOP PRESS. I see you applied
> my patch ;). Thanks.
>
> In which case, for non-legacy devices we should definitely be using
> VIRTIO_F_IOMMU_PLATFORM, but since this platform hasn't yet moved to the
> world of flying cars, could we unconditionally set the DMA ops on ARM
> for legacy devices? The alternative is disabling the SMMU altogether,
> but that's less than ideal because there are non-virtio devices on the
> same PCI bus.
>
> Will
I'd rather people didn't use SMMU with legacy devices.
Can't you guys just code up the virtio 1 layout in QEMU?
I took a look and it's not a big deal now that two other
transports converted, except mmio code in QEMU doesn't
use linux header to it's a bit messy.
I'll send a patch to clean that up.
--
MST
next prev parent reply other threads:[~2017-01-12 22:12 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-10 17:51 [PATCH v2 1/2] virtio_mmio: Set DMA masks appropriately Robin Murphy
2017-01-10 17:51 ` [PATCH v2 2/2] vring: Force use of DMA API for ARM-based systems Robin Murphy
2017-01-10 23:33 ` Michael S. Tsirkin
2017-01-11 10:01 ` Will Deacon
2017-01-11 18:12 ` Andy Lutomirski
2017-01-13 9:40 ` Will Deacon
2017-01-13 16:59 ` Michael S. Tsirkin
2017-01-12 22:12 ` Michael S. Tsirkin [this message]
2017-01-13 9:25 ` Will Deacon
2017-01-13 16:46 ` Michael S. Tsirkin
2017-01-13 17:21 ` Will Deacon
2017-01-13 18:23 ` Michael S. Tsirkin
2017-01-16 10:40 ` Will Deacon
2017-01-16 14:18 ` Michael S. Tsirkin
2017-01-16 14:21 ` Will Deacon
2017-01-16 14:27 ` Michael S. Tsirkin
2017-01-16 14:34 ` Will Deacon
2017-01-19 21:51 ` Michael S. Tsirkin
2017-01-20 10:33 ` Will Deacon
2017-01-24 16:04 ` Marc Zyngier
[not found] ` <5ad8ce42-a469-7417-d2c5-58cc0da89e8d@arm.com>
2017-01-24 16:06 ` Michael S. Tsirkin
2017-01-24 16:10 ` Marc Zyngier
2017-01-10 23:30 ` [PATCH v2 1/2] virtio_mmio: Set DMA masks appropriately Michael S. Tsirkin
2017-01-11 10:31 ` Jean-Philippe Brucker
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