From: Andy Lutomirski <luto@kernel.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Andy Lutomirski <luto@kernel.org>, Joerg Roedel <joro@8bytes.org>,
Ingo Molnar <mingo@kernel.org>, "H . Peter Anvin" <hpa@zytor.com>,
X86 ML <x86@kernel.org>, LKML <linux-kernel@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Dave Hansen <dave.hansen@intel.com>,
Josh Poimboeuf <jpoimboe@redhat.com>,
Juergen Gross <jgross@suse.com>,
Peter Zijlstra <peterz@infradead.org>,
Borislav Petkov <bp@alien8.de>, Jiri Kosina <jkosina@suse.cz>,
Boris Ostrovsky <boris.ostrovsky@oracle.com>,
Brian Gerst <brgerst@gmail.com>,
David Laight <David.Laight@aculab.com>,
Denys Vlasenko <dvlasenk@redhat.com>,
Eduardo Valentin <eduval@amazon.com>,
Greg KH <gregkh@linuxfoundation.org>,
Will Deacon <will.deacon@arm.com>,
"Liguori, Anthony" <aliguori@amazon.com>,
Daniel Gruss <daniel.gruss@iaik.tugraz.at>,
Hugh Dickins <hughd@google.com>, Kees Cook <keescook@google.com>,
Andrea Arcangeli <aarcange@redhat.com>,
Waiman Long <llong@redhat.com>, Pavel Machek <pavel@ucw.cz>,
"David H . Gutteridge" <dhgutteridge@sympatico.ca>,
Joerg Roedel <jroedel@suse.de>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>
Subject: Re: [PATCH 1/3] perf/core: Make sure the ring-buffer is mapped in all page-tables
Date: Fri, 20 Jul 2018 12:33:14 -0700 [thread overview]
Message-ID: <CALCETrW7o=s7esmE4+SxLPsLv2SvJZU6f7jfsedazZVrot2EqA@mail.gmail.com> (raw)
In-Reply-To: <alpine.DEB.2.21.1807202126400.1694@nanos.tec.linutronix.de>
On Fri, Jul 20, 2018 at 12:27 PM, Thomas Gleixner <tglx@linutronix.de> wrote:
> On Fri, 20 Jul 2018, Andy Lutomirski wrote:
>> > On Jul 20, 2018, at 6:22 AM, Joerg Roedel <joro@8bytes.org> wrote:
>> >
>> > From: Joerg Roedel <jroedel@suse.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.
next prev parent reply other threads:[~2018-07-20 19:33 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-20 16:22 [PATCH 0/3] PTI for x86-32 Fixes and Updates Joerg Roedel
2018-07-20 16:22 ` [PATCH 1/3] perf/core: Make sure the ring-buffer is mapped in all page-tables Joerg Roedel
2018-07-20 17:06 ` Andy Lutomirski
2018-07-20 17:48 ` Joerg Roedel
2018-07-20 19:32 ` Andy Lutomirski
2018-07-20 21:37 ` Joerg Roedel
2018-07-20 22:20 ` Andy Lutomirski
2018-07-21 21:06 ` Linus Torvalds
2018-07-20 19:27 ` Thomas Gleixner
2018-07-20 19:33 ` Andy Lutomirski [this message]
2018-07-20 19:43 ` Thomas Gleixner
2018-07-20 19:53 ` Thomas Gleixner
2018-07-20 16:22 ` [PATCH 2/3] x86/entry/32: Check for VM86 mode in slow-path check Joerg Roedel
2018-07-21 16:06 ` Pavel Machek
2018-07-20 16:22 ` [PATCH 3/3] x86/entry/32: Copy only ptregs on paranoid entry/exit path Joerg Roedel
2018-07-20 17:09 ` Andy Lutomirski
2018-07-20 21:42 ` Joerg Roedel
2018-07-23 3:49 ` [PATCH 0/3] PTI for x86-32 Fixes and Updates David H. Gutteridge
2018-07-23 7:29 ` Joerg Roedel
2018-07-26 3:47 ` David H. Gutteridge
2018-07-23 14:09 ` Pavel Machek
2018-07-23 19:00 ` Linus Torvalds
2018-07-23 21:38 ` Pavel Machek
2018-07-23 21:50 ` Andy Lutomirski
2018-07-23 21:55 ` Pavel Machek
2018-07-24 21:18 ` Pavel Machek
2018-07-23 21:59 ` Josh Poimboeuf
2018-07-23 22:07 ` Dave Hansen
2018-07-24 13:39 ` Pavel Machek
2018-07-24 14:39 ` Andy Lutomirski
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