On Fri, 20 Jul 2018, Andy Lutomirski wrote: > On Fri, Jul 20, 2018 at 12:27 PM, Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote: > > On Fri, 20 Jul 2018, Andy Lutomirski wrote: > >> > On Jul 20, 2018, at 6:22 AM, Joerg Roedel <joro@xxxxxxxxxx> wrote: > >> > > >> > From: Joerg Roedel <jroedel@xxxxxxx> > >> > > >> > The ring-buffer is accessed in the NMI handler, so we better > >> > avoid faulting on it. Sync the vmalloc range with all > >> > page-tables in system to make sure everyone has it mapped. > >> > > >> > This fixes a WARN_ON_ONCE() that can be triggered with PTI > >> > enabled on x86-32: > >> > > >> > WARNING: CPU: 4 PID: 0 at arch/x86/mm/fault.c:320 vmalloc_fault+0x220/0x230 > >> > > >> > This triggers because with PTI enabled on an PAE kernel the > >> > PMDs are no longer shared between the page-tables, so the > >> > vmalloc changes do not propagate automatically. > >> > >> It seems like it would be much more robust to fix the vmalloc_fault() > >> code instead. > > > > Right, but now the obvious fix for the issue at hand is this. We surely > > should revisit this. > > If you commit this under this reasoning, then please at least make it say: > > /* XXX: The vmalloc_fault() code is buggy on PTI+PAE systems, and this > is a workaround. */ > > Let's not have code in the kernel that pretends to make sense but is > actually voodoo magic that works around bugs elsewhere. It's no fun > to maintain down the road. Fair enough. Lemme amend it. Joerg is looking into it, but I surely want to get that stuff some exposure in next ASAP. Thanks, tglx
