On Tue, Feb 24, 2015 at 10:51 AM, Denys Vlasenko <[email protected]> wrote: > PER_CPU(old_rsp) usage is simplified - now it is used only > as temp storage, and userspace stack pointer is immediately stored > in pt_regs->sp on syscall entry, instead of being used later, > on syscall exit. This allows to get rid of thread_struct::usersp.
I'm not seeing any performance loss here, which is good. This is a nice cleanup. > @@ -253,11 +247,13 @@ GLOBAL(system_call_after_swapgs) > */ > ENABLE_INTERRUPTS(CLBR_NONE) > ALLOC_PT_GPREGS_ON_STACK 6*8 /* 6*8: space for orig_ax and iret frame > */ > + movq %rcx,RIP(%rsp) > + movq %r11,EFLAGS(%rsp) > + movq PER_CPU_VAR(old_rsp),%rcx > + movq %rcx,RSP(%rsp) It's a bit unfortunate that this adds two instructions instead of just one. I guess this gets fix when we start using push instead of mov here. (And, if we use push, then we can fix up the RCX slot for free, too.) Acked-by me, but I won't apply it until v2 to avoid messy rebases. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
