On Fri, Feb 03, 2017 at 05:49:11AM +0200, Michael S. Tsirkin wrote: > 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@xxxxxxx> > Cc: <stable@xxxxxxxxxxxxxxx> > Signed-off-by: Will Deacon <will.deacon@xxxxxxx> > Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx> > Acked-by: Marc Zyngier <marc.zyngier@xxxxxxx> > --- > > I'll merge this for 4.10. Let's fix it properly for 4.11. Acked-by: Will Deacon <will.deacon@xxxxxxx> Will -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html