On Tue, Aug 27, 2019 at 10:14:17PM +0100, Matthew Garrett wrote: > Apple have provided a sysctl that allows applications to indicate that > specific threads should make use of core isolation while allowing > the rest of the system to make use of SMT, and browsers (Safari, Firefox > and Chrome, at least) are now making use of this. Trying to do something > similar using cgroups seems a bit awkward. Would something like this be > reasonable?
Sure; like I wrote earlier; I only did the cgroup thing because I was lazy and it was the easiest interface to hack on in a hurry. The rest of the ABI nonsense can 'trivially' be done later; if when we decide to actually do this. And given MDS, I'm still not entirely convinced it all makes sense. If it were just L1TF, then yes, but now... > Having spoken to the Chrome team, I believe that the > semantics we want are: > > 1) A thread to be able to indicate that it should not run on the same > core as anything not in posession of the same cookie > 2) Descendents of that thread to (by default) have the same cookie > 3) No other thread be able to obtain the same cookie > 4) Threads not be able to rejoin the global group (ie, threads can > segregate themselves from their parent and peers, but can never rejoin > that group once segregated) > > but don't know if that's what everyone else would want. > > diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h > index 094bb03b9cc2..5d411246d4d5 100644 > --- a/include/uapi/linux/prctl.h > +++ b/include/uapi/linux/prctl.h > @@ -229,4 +229,5 @@ struct prctl_mm_map { > # define PR_PAC_APDBKEY (1UL << 3) > # define PR_PAC_APGAKEY (1UL << 4) > > +#define PR_CORE_ISOLATE 55 > #endif /* _LINUX_PRCTL_H */ > diff --git a/kernel/sys.c b/kernel/sys.c > index 12df0e5434b8..a054cfcca511 100644 > --- a/kernel/sys.c > +++ b/kernel/sys.c > @@ -2486,6 +2486,13 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, > arg2, unsigned long, arg3, > return -EINVAL; > error = PAC_RESET_KEYS(me, arg2); > break; > + case PR_CORE_ISOLATE: > +#ifdef CONFIG_SCHED_CORE > + current->core_cookie = (unsigned long)current; This needs to then also force a reschedule of current. And there's the little issue of what happens if 'current' dies while its children live on, and current gets re-used for a new process and does this again. > +#else > + result = -EINVAL; > +#endif > + break; > default: > error = -EINVAL; > break; > > > -- > Matthew Garrett | mj...@srcf.ucam.org