On Fri, Jun 27, 2014 at 12:55 PM, Oleg Nesterov <oleg@xxxxxxxxxx> wrote: > On 06/27, Andy Lutomirski wrote: >> >> On Fri, Jun 27, 2014 at 12:27 PM, Oleg Nesterov <oleg@xxxxxxxxxx> wrote: >> > On 06/27, Kees Cook wrote: >> >> >> >> It looks like SMP ARM issues dsb for rmb, which seems a bit expensive. >> >> http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0204g/CIHJFGFE.htm >> >> >> >> ... >> >> >> >> I really want to avoid adding anything to the secure_computing() >> >> execution path. :( >> > >> > I must have missed something but I do not understand your concerns. >> > >> > __secure_computing() is not trivial, and we are going to execute the >> > filters. Do you really think rmb() can add the noticeable difference? >> > >> > Not to mention that we can only get here if we take the slow syscall >> > enter path due to TIF_SECCOMP... >> > >> >> On my box, with my fancy multi-phase seccomp patches, the total >> seccomp overhead for a very short filter is about 13ns. Adding a full >> barrier would add several ns, I think. > > I am just curious, does this 13ns overhead include the penalty from the > slow syscall enter path triggered by TIF_SECCOMP ? Yes, which is more or less the whole point of that patch series. I rewrote part of the TIF_SECCOMP-but-no-tracing case in assembly :) I'm playing with rewriting it in C, but it's looking like it'll be a bit more far-reaching than I was hoping. --Andy
