On Wed, Jan 11, 2017 at 10:12:36AM -0800, Andy Lutomirski wrote: > On Wed, Jan 11, 2017 at 2:01 AM, Will Deacon <will.dea...@arm.com> 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.dea...@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 <l...@kernel.org> > >> > Cc: Michael S. Tsirkin <m...@redhat.com> > >> > Signed-off-by: Will Deacon <will.dea...@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. > > Also, on ARM, using the DMA API appears to *always* be the correct > approach. Why not do it all the time, then? The non-DMA-API path is > a legacy thing that is needed because a few platforms incorrectly > enumerate their IOMMUs. ARM gets it right, so I don't see why ARM > should be subject to the legacy mess.
I didn't realize ARM gets this right. QEMU still pokes at physical addresses directly in legacy mode so I wonder how could that be the case. I'll try to find out. > Even on x86, it should be possible to get the code into a state where > using DMA ops is always correct. > > --Andy This I could totally get behind. A driver would install some per device flag to make it figure out IOMMU does not apply, and in a portable way since at least x86 and PPC need this, maybe more. This would/should also handle the bug that admin can bind vfio to legacy virtio devices even without the noiommu mode. -- MST _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization