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linux/drivers/virtio
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Will Deacon c7070619f3 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: 876945dbf6 ("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>
2017-01-25 00:33:11 +02:00
..
Kconfig docs: fix locations of several documents that got moved 2016-10-24 08:12:35 -02:00
Makefile
virtio_balloon.c virtio: update balloon size in balloon "probe" 2016-10-31 00:21:41 +02:00
virtio_input.c
virtio_mmio.c virtio_mmio: Set DMA masks appropriately 2017-01-25 00:33:10 +02:00
virtio_pci_common.c virtio_pci: split vp_try_to_find_vqs into INTx and MSI-X variants 2016-12-16 00:12:49 +02:00
virtio_pci_common.h virtio_pci: use pci_alloc_irq_vectors 2016-12-16 00:12:47 +02:00
virtio_pci_legacy.c virtio_pci: Limit DMA mask to 44 bits for legacy virtio devices 2016-10-31 00:21:39 +02:00
virtio_pci_modern.c virtio_pci_modern: fix complaint by sparse 2016-12-15 06:39:46 +02:00
virtio_ring.c vring: Force use of DMA API for ARM-based systems with legacy devices 2017-01-25 00:33:11 +02:00
virtio.c