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

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Message-ID: <CA+55aFyjFjdeAwAOu-WsE=yk_+cAaaOvp4-DSEHDaWG+1g_BSA@mail.gmail.com>
Date:   Sat, 21 Jul 2018 14:06:52 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Joerg Roedel <jroedel@...e.de>,
        Andrew Lutomirski <luto@...nel.org>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>, Peter Anvin <hpa@...or.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Jürgen Groß <jgross@...e.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>, Jiri Kosina <jkosina@...e.cz>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Brian Gerst <brgerst@...il.com>,
        David Laight <David.Laight@...lab.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Eduardo Valentin <eduval@...zon.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Will Deacon <will.deacon@....com>,
        "Liguori, Anthony" <aliguori@...zon.com>,
        Daniel Gruss <daniel.gruss@...k.tugraz.at>,
        Hugh Dickins <hughd@...gle.com>,
        Kees Cook <keescook@...gle.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Waiman Long <llong@...hat.com>, Pavel Machek <pavel@....cz>,
        "David H . Gutteridge" <dhgutteridge@...patico.ca>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>
Subject: Re: [PATCH 1/3] perf/core: Make sure the ring-buffer is mapped in all page-tables

On Fri, Jul 20, 2018 at 3:20 PM Andy Lutomirski <luto@...capital.net> wrote:
> Thanks for digging!  The problem was presumably that vmalloc_fault() will IRET and re-enable NMIs on the way out.
>  But we’ve supported page faults on user memory in NMI handlers on 32-bit and 64-bit for quite a while, and it’s 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