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| author | Michael S. Tsirkin <mst@redhat.com> | 2017-02-03 05:43:52 +0200 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2017-02-09 08:08:28 +0100 |
| commit | 449d3ecfbd7640dc763dbf333131858ead6c3f11 (patch) | |
| tree | 4de2a5d72a77191f06fefb1d11ab9582a96f0259 /drivers | |
| parent | 16f61dee7e7cb378216ff59ffeacf157efad6c82 (diff) | |
| download | linux-rt-449d3ecfbd7640dc763dbf333131858ead6c3f11.tar.gz | |
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')
| -rw-r--r-- | drivers/virtio/virtio_ring.c | 7 |
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; } |