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

[Paolo Bonzini]

On 15/12/2014 13:56, Mark Burton wrote:
> A third proposal is to mark pages as IO when a ld/st ex is performed to
> them. Then to augment the memory API to indicate that a ld/st ex is in
> hand, allowing the memory chain to decide if it should allow the write
> or cause a fault. This would seem to be the closest approach to the real
> H/W. However it means marking pages as IO (which could cause us issues
> if there was code on that page?, or slow things down) - and it means
> adding to the memory API.

What are the intended semantics for reads/writes from the outside world?
 Should they cause the ll/sc pair to retry or not?

If not, it should not need any change to the memory API; you can do it
entirely within cputlb.c, roughly the same as the handling of
TLB_NOTDIRTY.  It also marks pages as I/O, but only internally within TCG.

Paolo