On Thu, May 11, 2017 at 11:58 PM, Ingo Molnar <mingo@xxxxxxxxxx> wrote: > > * Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > >> On Thu, May 11, 2017 at 4:17 PM, Thomas Garnier <thgarnie@xxxxxxxxxx> wrote: >> > >> > Ingo: Do you want the change as-is? Would you like it to be optional? >> > What do you think? >> >> I'm not ingo, but I don't like that patch. It's in the wrong place - >> that system call return code is too timing-critical to add address >> limit checks. >> >> Now what I think you *could* do is: >> >> - make "set_fs()" actually set a work flag in the current thread flags >> >> - do the test in the slow-path (syscall_return_slowpath). >> >> Yes, yes, that ends up being architecture-specific, but it's fairly simple. >> >> And it only slows down the system calls that actually use "set_fs()". >> Sure, it will slow those down a fair amount, but they are hopefully a >> small subset of all cases. >> >> How does that sound to people? Thats' where we currently do that >> >> if (IS_ENABLED(CONFIG_PROVE_LOCKING) && >> WARN(irqs_disabled(), "syscall %ld left IRQs disabled", >> regs->orig_ax)) >> local_irq_enable(); >> >> check too, which is a fairly similar issue. > > I really like that idea and I'd be perfectly fine with that solution, because it > puts the overhead where the problem comes from, and adds an extra incentive for > code to move away from set_fs() facilities. Win-win. Great, I will adapt the patch for that. > > Thanks, > > Ingo -- Thomas -- To unsubscribe from this list: send the line "unsubscribe linux-s390" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
