On Mon, Oct 20, 2014 at 10:41 PM, Borislav Petkov <b...@alien8.de> wrote: > On Thu, Oct 16, 2014 at 09:21:42AM -0700, Andy Lutomirski wrote: >> I think it's the same as in the other case in switch_mm. leave_mm does >> cpumask_clear_cpu(cpu, mm_cpumask(active_mm)), and, once that has >> happened, modify_ldt won't send an IPI to this CPU. So, if leave_mm >> runs, and then another CPU calls modify_ldt on the mm that is in lazy >> mode here, it won't update our LDT register, so the LDT register and >> prev->context.ldt might not match. > > Ok, let me see if I can follow with an example: > > We call leave_mm() on, say, cpu 3 and mm_cpumask(active_mm) has cpu 3 and > 4 set. Then, on cpu 4 we call modify_ldt on that same mm and there in > alloc_ldt() we have this: > > if (!cpumask_equal(mm_cpumask(current->mm), > cpumask_of(smp_processor_id()))) > smp_call_function(flush_ldt, current->mm, 1); > > and since we've cleared cpu 3 from the cpumask, we don't flush_ldt() > on it and there you have the difference. > > Am I close?
You're exactly correct, or at least you seem to understand it the way I do :) --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
