On Tue, Jan 10, 2017 at 05:51:18PM +0000, Robin Murphy wrote: > From: Will Deacon <will.deacon@xxxxxxx> > > 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@xxxxxxxxxx> > Cc: Michael S. Tsirkin <mst@xxxxxxxxxx> > Signed-off-by: Will Deacon <will.deacon@xxxxxxx> 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. > --- > drivers/virtio/virtio_ring.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c > index 409aeaa49246..447245f2c813 100644 > --- a/drivers/virtio/virtio_ring.c > +++ b/drivers/virtio/virtio_ring.c > @@ -159,6 +159,10 @@ 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 */ > + if (IS_ENABLED(CONFIG_ARM) || IS_ENABLED(CONFIG_ARM64)) > + return true; > + > return false; > } > > -- > 2.10.2.dirty _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
