On Fri, Jul 20, 2018 at 10:06:54AM -0700, 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. The question is whether the NMI path is nesting-safe, then we can remove the WARN_ON_ONCE(in_nmi()) in the vmalloc_fault path. It should be nesting-safe on x86-32 because of the way the stack-switch happens there. If its also nesting-safe on x86-64 the warning there can be removed. Or did you think of something else to fix there? Thanks, Joerg
