On Tue, Mar 27, 2018 at 11:21:17AM +0100, Will Deacon wrote: > On Sun, Mar 25, 2018 at 08:50:04PM +0300, Yury Norov wrote: > > kick_all_cpus_sync() forces all CPUs to sync caches by sending broadcast > > IPI. > > If CPU is in extended quiescent state (idle task or nohz_full userspace), > > this > > work may be done at the exit of this state. Delaying synchronization helps > > to > > save power if CPU is in idle state and decrease latency for real-time tasks. > > > > This patch introduces kick_active_cpus_sync() and uses it in mm/slab and > > arm64 > > code to delay syncronization. > > > > For task isolation (https://lkml.org/lkml/2017/11/3/589), IPI to the CPU > > running > > isolated task would be fatal, as it breaks isolation. The approach with > > delaying > > of synchronization work helps to maintain isolated state. > > > > I've tested it with test from task isolation series on ThunderX2 for more > > than > > 10 hours (10k giga-ticks) without breaking isolation. > > > > Signed-off-by: Yury Norov <yno...@caviumnetworks.com> > > --- > > arch/arm64/kernel/insn.c | 2 +- > > include/linux/smp.h | 2 ++ > > kernel/smp.c | 24 ++++++++++++++++++++++++ > > mm/slab.c | 2 +- > > 4 files changed, 28 insertions(+), 2 deletions(-) > > > > diff --git a/arch/arm64/kernel/insn.c b/arch/arm64/kernel/insn.c > > index 2718a77da165..9d7c492e920e 100644 > > --- a/arch/arm64/kernel/insn.c > > +++ b/arch/arm64/kernel/insn.c > > @@ -291,7 +291,7 @@ int __kprobes aarch64_insn_patch_text(void *addrs[], > > u32 insns[], int cnt) > > * synchronization. > > */ > > ret = aarch64_insn_patch_text_nosync(addrs[0], > > insns[0]); > > - kick_all_cpus_sync(); > > + kick_active_cpus_sync(); > > return ret; > > } > > } > > I think this means that runtime modifications to the kernel text might not > be picked up by CPUs coming out of idle. Shouldn't we add an ISB on that > path to avoid executing stale instructions?
Thanks, Will, for the hint. I'll do that. Yury
