On Tue, Aug 01, 2017 at 07:15:40AM -0700, Andy Lutomirski wrote: > On Tue, Aug 1, 2017 at 7:02 AM, Mathieu Desnoyers > <mathieu.desnoyers@xxxxxxxxxxxx> wrote: > > /* > > * The full memory barrier implied by mm_cpumask update operations > > * is required by the membarrier system call. > > */ > > > > What we want to order here is: > > > > prev userspace memory accesses > > schedule > > <full mb> (it's already there) [A] > > update to rq->curr changing the rq->curr->mm value > > <full mb> (provided by mm_cpumask updates in switch_mm on x86) [B] > > If I understand this right, the issue with relying on CR3 writes is > that the target CPU could switch to a kernel thread and back to the > same user mm white the membarrier caller is reading its mm, right? The thing that got my attention was your patch removing the load_cr3(). Ah, looking closer, it appears that you have not eliminated the CR3 load, but just renamed it to write_cr3(). So if there is always still a CR3 load, you are right, I should be able to simply move the comment. Or let you insert the comment into your patch? So there is still always a CR3 load, correct? (Hey, I thought that maybe x86 was moving to ASIDs or some such.) Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe linux-next" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
