> On Dec 31, 2018, at 12:08 PM, Andy Lutomirski <l...@kernel.org> wrote: > > On Sun, Dec 30, 2018 at 11:20 PM Nadav Amit <na...@vmware.com> wrote: >> It is sometimes beneficial to have a restartable sequence - very few >> instructions which if they are preempted jump to a predefined point. >> >> To provide such functionality on x86-64, we use an empty REX-prefix >> (opcode 0x40) as an indication for instruction in such a sequence. Before >> calling the schedule IRQ routine, if the "magic" prefix is found, we >> call a routine to adjust the instruction pointer. It is expected that >> this opcode is not in common use. >> >> The following patch will make use of this function. Since there are no >> other users (yet?), the patch does not bother to create a general >> infrastructure and API that others can use for such sequences. Yet, it >> should not be hard to make such extension later. > > The following patch does not use it. Can you update this?
I will. Sorry for not updating the commit-log. The GCC plugin, and various requests (that I am not sure I fully agree with) really caused me to spit some blood. >> +asmlinkage __visible void restart_kernel_rseq(struct pt_regs *regs) >> +{ >> + if (user_mode(regs) || *(u8 *)regs->ip != KERNEL_RESTARTABLE_PREFIX) >> + return; > > else? > > I suspect something is missing here. Or I'm very confused. Indeed, the code should call optpoline_restart_rseq() (or some other name, once I fix the naming). I will fix it.