Re: [Qemu-devel] Atomic Instructions - comments please

[Peter Maydell]

On 15 December 2014 at 12:56, Mark Burton <address@hidden> wrote:
> One proposal is ‘simply’ to add a mutex around this code, such
> that multi-threaded TCG will correctly update/read these saved
> address/values.
> This _should_ maintain the status-quo. Things that were broken
> before will remain broken, nothing new should break. The concern
> is that the fact that the TCG was previously uni-threaded MAY be
> masking problems with this code that we are not taking into account.

Personally I would start out with this approach. We're going to
need a "do this whole sequence atomically wrt other guest CPUs"
mechanism anyway, so it's not implementing something we wouldn't
otherwise need. And it's the simple thing to do. It's certainly
possible to do a more architecturally correct ld/st exclusive
implementation along the lines of how we manage TB invalidation
with the dirty bitmap, but if we can do without it then we
should try to keep the scope of this project constrained: it's
a big enough job as it is.

-- PMM