On 29 February 2016 at 13:50, Paolo Bonzini <pbonz...@redhat.com> wrote: > > > On 29/02/2016 14:21, Peter Maydell wrote: >> On 29 February 2016 at 13:16, Alvise Rigo <a.r...@virtualopensystems.com> >> wrote: >>> > As in the case of tlb_flush(), also tlb_flush_by_mmuidx has to query the >>> > TLB flush if it targets another VCPU. To accomplish this, a new async >>> > work has been added, together with a new TLBFlushByMMUIdxParams. A >>> > bitmap is used to track the MMU indexes to flush. >>> > >>> > This patch applies to the multi_tcg_v8 branch. >> What's the API for a target CPU emulation to say "and now I must >> wait for the TLB op to finish" before completing this guest >> instruction? > > My proposal has been for a while for DMB to put the CPU in a halted > state (remote TLB callbacks then can decrement a counter and signal > cpu_halt_cond when it's zero), but no one has implemented this.
Yeah, that's the other approach -- really split the things that can be async and do real "wait for completion" at points which must synchronize. (Needs a little care since DMB is not the only such point.) An initial implementation that does an immediate wait-for-completion is probably simpler to review though, and add the real asynchrony later. And either way you need an API for the target to wait for completion. thanks -- PMM