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

[alvise rigo]

I see the risk. I will come back with something and let you know.

Thank you,
alvise

On Mon, Feb 29, 2016 at 3:06 PM, Paolo Bonzini <address@hidden> wrote:
>
>
> On 29/02/2016 15:02, alvise rigo wrote:
>> > 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.
>> OK, so basically being sure that the target CPU performs the flush
>> before executing the next TB is not enough. We need a sort of feedback
>> that the flush has been done before emulating the next guest
>> instruction. Did I get it right?
>
> That risks getting deadlocks if CPU A asks B to flush the TLB and vice
> versa.  Using a halted state means that the VCPU thread goes through the
> cpus.c loop and can for example service other CPUs' TLB flush requests.
>
> Paolo