vring: Force use of DMA API for ARM-based systems with legacy devices
authorWill Deacon <will.deacon@arm.com>
Fri, 20 Jan 2017 10:33:32 +0000 (10:33 +0000)
committerMichael S. Tsirkin <mst@redhat.com>
Tue, 24 Jan 2017 22:33:11 +0000 (00:33 +0200)
commitc7070619f3408d9a0dffbed9149e6f00479cf43b
tree5f8f21661f346e58f3de1f9eebec9fa3e45a1566
parentf7f6634d23830ff74335734fbdb28ea109c1f349
vring: Force use of DMA API for ARM-based systems with legacy devices

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 legacy virtio-blk device 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 legacy virtio devices.
Modern devices can advertise the prescense of an IOMMU using the
VIRTIO_F_IOMMU_PLATFORM feature flag.

Cc: Andy Lutomirski <luto@kernel.org>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: <stable@vger.kernel.org>
Fixes: 876945dbf649 ("arm64: Hook up IOMMU dma_ops")
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
drivers/virtio/virtio_ring.c