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

[Linus Torvalds]

On Fri, Jul 20, 2018 at 3:20 PM Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
> Thanks for digging!  The problem was presumably that vmalloc_fault() will IRET and re-enable NMIs on the way out.
>  But weâve supported page faults on user memory in NMI handlers on 32-bit and 64-bit for quite a while, and itâs fine now.
>
> I would remove the warning, re-test, and revert the other patch.

Agreed. I don't think we have any issues with page faults during NMI
any more.  Afaik the kprobe people depend on it.

That said, 64-bit mode has that scary PV-op case
(arch_flush_lazy_mmu_mode). Being PV mode, I can't find it in myself
to worry about it, I'm assuming it's ok.

                Linus