Re: [Qemu-devel] [PATCH 2/3] cputlb: serialize tlb updates with env->tlb_lock

[Emilio G. Cota]

On Wed, Oct 03, 2018 at 19:05:51 +0200, Paolo Bonzini wrote:
> On 03/10/2018 19:02, Emilio G. Cota wrote:
> >> For reads I agree, but you may actually get a torn read if the writer
> >> doesn't use atomic_set.
> >
> > But you cannot get a torn read if all reads that don't hold the lock
> > are coming from the same thread that performed the write.
> 
> Ah, so you are relying on copy_tlb_helper(_locked) being invoked only
> from the vCPU thread (as opposed to someone else doing tlb_flush)?

Yes. tlb_flush_nocheck is always run by the owner thread--tlb_flush
checks for this, and if !qemu_cpu_is_self(cpu) then it schedules
async work on the owner thread.

> Maybe it's worth adding a comment if that's what I missed.

I'll send a v2 with an updated comment and a debug-only assert
in the copy helper.

Thanks,

                E.