On 15 December 2014 at 13:28, Paolo Bonzini <pbonz...@redhat.com> wrote: > > > On 15/12/2014 14:23, Peter Maydell wrote: >> > 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. > > No, I mean from DMA. Other CPU of course need to abort reads/writes.
Depends whether the DMAing device is in the same shareability domain. Sufficiently clever DMA devices (probably ones which do cache-coherent DMA; GPUs spring to mind as a possibility) probably would; plain old DMA devices not. In practice anybody trying to do DMA onto an ll/sc mutex location is out of their mind and we can ignore this possibility. -- PMM
