[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <alpine.DEB.2.21.1807202142130.1694@nanos.tec.linutronix.de>
Date: Fri, 20 Jul 2018 21:43:16 +0200 (CEST)
From: Thomas Gleixner <tglx@...utronix.de>
To: Andy Lutomirski <luto@...nel.org>
cc: Joerg Roedel <joro@...tes.org>, Ingo Molnar <mingo@...nel.org>,
"H . Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>,
LKML <linux-kernel@...r.kernel.org>,
Linux-MM <linux-mm@...ck.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Dave Hansen <dave.hansen@...el.com>,
Josh Poimboeuf <jpoimboe@...hat.com>,
Juergen 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 KH <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>,
Joerg Roedel <jroedel@...e.de>,
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, 20 Jul 2018, Andy Lutomirski wrote:
> On Fri, Jul 20, 2018 at 12:27 PM, Thomas Gleixner <tglx@...utronix.de> wrote:
> > On Fri, 20 Jul 2018, Andy Lutomirski wrote:
> >> > On Jul 20, 2018, at 6:22 AM, Joerg Roedel <joro@...tes.org> wrote:
> >> >
> >> > From: Joerg Roedel <jroedel@...e.de>
> >> >
> >> > 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
Powered by blists - more mailing lists