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authorMichael S. Tsirkin <mst@redhat.com>2017-02-03 05:43:52 +0200
committerMichael S. Tsirkin <mst@redhat.com>2017-02-03 23:38:50 +0200
commit0d5415b489f68b58e1983a53793d25d53098ed4b (patch)
tree9509a05b5c480b84214714698cffb85943be8124 /net/ipv4/tcp_illinois.c
parent566cf877a1fcb6d6dc0126b076aad062054c2637 (diff)
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>
Diffstat (limited to 'net/ipv4/tcp_illinois.c')
0 files changed, 0 insertions, 0 deletions
by adding a NULL pointer check and a WARN_ON_ONCE() to avoid the oops that would then generally make the machine unresponsive. Other callers of i915_gem_object_to_ggtt() seem to also check for the returned pointer being NULL and warn about it, so this clearly has happened before in other places. [ Reported it originally to the i915 developers on Jan 8, applying the ugly workaround on my own now after triggering the problem for the second time with no feedback. This is likely to be the same bug reported as https://bugs.freedesktop.org/show_bug.cgi?id=98829 https://bugs.freedesktop.org/show_bug.cgi?id=99134 which has a patch for the underlying problem, but it hasn't gotten to me, so I'm applying the workaround. ] Cc: Daniel Vetter <daniel.vetter@intel.com> Cc: Jani Nikula <jani.nikula@linux.intel.com> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com> Cc: Chris Wilson <chris@chris-wilson.co.uk> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Imre Deak <imre.deak@intel.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'net/packet/internal.h')