Re: [Qemu-devel] [mttcg] cputlb: Use async tlb_flush_by_mmuidx

[Peter Maydell <peter.maydell@linaro.org>]

On 29 February 2016 at 13:50, Paolo Bonzini <pbonzini@redhat.com> wrote:
>
>
> On 29/02/2016 14:21, Peter Maydell wrote:
>> On 29 February 2016 at 13:16, Alvise Rigo <a.rigo@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