On Sat, Feb 22, 2020 at 08:19:16PM +0000, Stefan Hajnoczi wrote: > The KVM_IOREGIONFD_POSTED_WRITES flag > skips waiting for an acknowledgement on write accesses. This is > suitable for accesses that do not require synchronous emulation, such as > doorbell register writes. I would avoid hacks like this until we understand this better. Specificlly one needs to be very careful since memory ordering semantics can differ between a write into an uncacheable range and host writes into a data structure. Reads from one region are also assumed to be ordered with writes to another region, and drivers are known to make assumptions like this. Memory ordering being what it is, this isn't a field I'd be comfortable device writes know what they are doing. -- MST
