In reply to this message I'll send two series' one for KVM and one for QEMU. The two series' are their respective component complements, and attempt to implement cache coherency for arm guests using emulated devices, where the emulator (qemu) uses cached memory for the device memory, but the guest uses uncached - as device memory is generally used. Right now I've just focused on VGA vram.
This approach is the "MADV_UNCACHED" type that Paolo suggested. This type of approach could also be described as "make userspace's memory access type match the expected access type of the guest", and Mario has suggested using a memory driver, which could have the same result. The coming series' is inspired by both Paolo's and Mario's suggestions, but it uses a kvm memslot flag, rather than an madvise flag, and thus for the memory driver, it's just KVM. See the thread https://lists.gnu.org/archive/html/qemu-devel/2015-03/msg01254.html for some more background. Thanks in advance for comments. drew
