On Fri, Sep 23, 2022 at 11:23:24PM +0200, Paolo Bonzini wrote: > Il ven 23 set 2022, 20:26 Peter Xu <peterx@xxxxxxxxxx> ha scritto: > > > > > Someone will show up with an old userspace which probes for the sole > > > existing capability, and things start failing subtly. It is quite > > > likely that the userspace code is built for all architectures, > > > > I didn't quite follow here. Since both kvm/qemu dirty ring was only > > supported on x86, I don't see the risk. > > Say you run a new ARM kernel on old userspace, and the new kernel uses > KVM_CAP_DIRTY_LOG_RING. Userspace will try to use the dirty page ring > buffer even though it lacks the memory barriers that were just > introduced in QEMU. > > The new capability means "the dirty page ring buffer is supported and, > by the way, you're supposed to do everything right with respect to > ordering of loads and stores; you can't get away without it like you > could on x86". I understand now, thanks both. -- Peter Xu _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
