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

[Peter Maydell]

On 15 December 2014 at 13:16, Paolo Bonzini <address@hidden> wrote:
> 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?

Assuming that by "outside world" you mean "some other CPU in this
cluster" [in ARM-speak, some other observer in the same shareability
domain]: writes should. Reads should not.

-- PMM