Re: [PATCH 1/3] perf/core: Make sure the ring-buffer is mapped in all page-tables

[Andy Lutomirski]

> 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.