Commit c7070619 authored by Will Deacon's avatar Will Deacon Committed by Michael S. Tsirkin

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

Cc: Andy Lutomirski <>
Cc: Michael S. Tsirkin <>
Cc: <>
Fixes: 876945db ("arm64: Hook up IOMMU dma_ops")
Signed-off-by: default avatarWill Deacon <>
Signed-off-by: Michael S. Tsirkin's avatarMichael S. Tsirkin <>
Acked-by: default avatarMarc Zyngier <>
parent f7f6634d
......@@ -159,6 +159,13 @@ static bool vring_use_dma_api(struct virtio_device *vdev)
if (xen_domain())
return true;
* On ARM-based machines, the DMA ops will do the right thing,
* so always use them with legacy devices.
return !virtio_has_feature(vdev, VIRTIO_F_VERSION_1);
return false;
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