Revert "vring: Force use of DMA API for ARM-based systems with legacy devices"

This reverts commit c7070619f3408d9a0dffbed9149e6f00479cf43b. This has been shown to regress on some ARM systems: by forcing on DMA API usage for ARM systems, we have inadvertently kicked open a hornets' nest in terms of cache-coherency. Namely that unless the virtio device is explicitly described as capable of coherent DMA by firmware, the DMA APIs on ARM and other DT-based platforms will assume it is non-coherent. This turns out to cause a big problem for the likes of QEMU and kvmtool, which generate virtio-mmio devices in their guest DTs but neglect to add the often-overlooked "dma-coherent" property; as a result, we end up with the guest making non-cacheable accesses to the vring, the host doing so cacheably, both talking past each other and things going horribly wrong. We are working on a safer work-around. Fixes: c7070619f340 ("vring: Force use of DMA API for ARM-based systems with legacy devices") Reported-by: Robin Murphy <robin.murphy@arm.com> Cc: <stable@vger.kernel.org> 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>
1 files changed, 0 insertions, 7 deletions
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
Age	Commit message (Collapse)	Author	Files	Lines
2013-03-15	all: import netsniff-ng 0.5.8-rc0 source	Daniel Borkmann	1	-0/+49
	We decided to get rid of the old Git history and start a new one for several reasons: ) Allow / enforce only high-quality commits (which was not the case for many commits in the history), have a policy that is more close to the one from the Linux kernel. With high quality commits, we mean code that is logically split into commits and commit messages that are signed-off and have a proper subject and message body. We do not allow automatic Github merges anymore, since they are total bullshit. However, we will either cherry-pick your patches or pull them manually. ) The old archive was about ~27MB for no particular good reason. This basically derived from the bad decision that also some PDF files where stored there. From this moment onwards, no binary objects are allowed to be stored in this repository anymore. The old archive is not wiped away from the Internet. You will still be able to find it, e.g. on git.cryptoism.org etc. Signed-off-by: Daniel Borkmann <dborkman@redhat.com> Signed-off-by: Tobias Klauser <tklauser@distanz.ch>