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authorMichael S. Tsirkin <mst@redhat.com>2017-02-03 05:43:52 +0200
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2017-02-09 08:08:28 +0100
commit449d3ecfbd7640dc763dbf333131858ead6c3f11 (patch)
tree4de2a5d72a77191f06fefb1d11ab9582a96f0259 /drivers/virtio
parent16f61dee7e7cb378216ff59ffeacf157efad6c82 (diff)
Revert "vring: Force use of DMA API for ARM-based systems with legacy devices"
commit 0d5415b489f68b58e1983a53793d25d53098ed4b upstream. 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> 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> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/virtio')
-rw-r--r--drivers/virtio/virtio_ring.c7
1 files changed, 0 insertions, 7 deletions
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index f1360487a594..489bfc61cf30 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -159,13 +159,6 @@ 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.
- */
- if (IS_ENABLED(CONFIG_ARM) || IS_ENABLED(CONFIG_ARM64))
- return !virtio_has_feature(vdev, VIRTIO_F_VERSION_1);
-
return false;
}