From: Andy Lutomirski <luto@amacapital.net>
To: "Luck, Tony" <tony.luck@intel.com>
Cc: Andy Lutomirski <luto@kernel.org>, Borislav Petkov <bp@alien8.de>,
X86 ML <x86@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Peter Zijlstra <peterz@infradead.org>,
Darren Hart <dvhart@infradead.org>,
LKML <linux-kernel@vger.kernel.org>,
linux-edac <linux-edac@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>
Subject: Re: [PATCH v2 1/3] x86/mce: Avoid infinite loop for copy from user recovery
Date: Tue, 12 Jan 2021 14:04:55 -0800 [thread overview]
Message-ID: <38AF04BE-7F39-450F-8C26-879C9934E3D6@amacapital.net> (raw)
In-Reply-To: <20210112205207.GA18195@agluck-desk2.amr.corp.intel.com>
> On Jan 12, 2021, at 12:52 PM, Luck, Tony <tony.luck@intel.com> wrote:
>
> On Tue, Jan 12, 2021 at 10:57:07AM -0800, Andy Lutomirski wrote:
>>> On Tue, Jan 12, 2021 at 10:24 AM Luck, Tony <tony.luck@intel.com> wrote:
>>>
>>> On Tue, Jan 12, 2021 at 09:21:21AM -0800, Andy Lutomirski wrote:
>>>> Well, we need to do *something* when the first __get_user() trips the
>>>> #MC. It would be nice if we could actually fix up the page tables
>>>> inside the #MC handler, but, if we're in a pagefault_disable() context
>>>> we might have locks held. Heck, we could have the pagetable lock
>>>> held, be inside NMI, etc. Skipping the task_work_add() might actually
>>>> make sense if we get a second one.
>>>>
>>>> We won't actually infinite loop in pagefault_disable() context -- if
>>>> we would, then we would also infinite loop just from a regular page
>>>> fault, too.
>>>
>>> Fixing the page tables inside the #MC handler to unmap the poison
>>> page would indeed be a good solution. But, as you point out, not possible
>>> because of locks.
>>>
>>> Could we take a more drastic approach? We know that this case the kernel
>>> is accessing a user address for the current process. Could the machine
>>> check handler just re-write %cr3 to point to a kernel-only page table[1].
>>> I.e. unmap the entire current user process.
>>
>> That seems scary, especially if we're in the middle of a context
>> switch when this happens. We *could* make it work, but I'm not at all
>> convinced it's wise.
>
> Scary? It's terrifying!
>
> But we know that the fault happend in a get_user() or copy_from_user() call
> (i.e. an RIP with an extable recovery address). Does context switch
> access user memory?
No, but NMI can.
The case that would be very very hard to deal with is if we get an NMI just before IRET/SYSRET and get #MC inside that NMI.
What we should probably do is have a percpu list of pending memory failure cleanups and just accept that we’re going to sometimes get a second MCE (or third or fourth) before we can get to it.
Can we do the cleanup from an interrupt? IPI-to-self might be a credible approach, if so.
next prev parent reply other threads:[~2021-01-12 22:06 UTC|newest]
Thread overview: 62+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-08 22:22 [PATCH 0/2] Fix infinite machine check loop in futex_wait_setup() Tony Luck
2021-01-08 22:22 ` [PATCH 1/2] x86/mce: Avoid infinite loop for copy from user recovery Tony Luck
2021-01-08 22:22 ` [PATCH 2/2] futex, x86/mce: Avoid double machine checks Tony Luck
2021-01-08 22:47 ` Peter Zijlstra
2021-01-08 23:08 ` Luck, Tony
2021-01-08 23:14 ` Peter Zijlstra
2021-01-08 23:20 ` Luck, Tony
2021-01-11 21:44 ` [PATCH v2 0/3] Fix infinite machine check loop in futex_wait_setup() Tony Luck
2021-01-11 21:44 ` [PATCH v2 1/3] x86/mce: Avoid infinite loop for copy from user recovery Tony Luck
2021-01-11 22:11 ` Andy Lutomirski
2021-01-11 22:20 ` Luck, Tony
2021-01-12 17:00 ` Andy Lutomirski
2021-01-12 17:16 ` Luck, Tony
2021-01-12 17:21 ` Andy Lutomirski
2021-01-12 18:23 ` Luck, Tony
2021-01-12 18:57 ` Andy Lutomirski
2021-01-12 20:52 ` Luck, Tony
2021-01-12 22:04 ` Andy Lutomirski [this message]
2021-01-13 1:50 ` Luck, Tony
2021-01-13 4:15 ` Andy Lutomirski
2021-01-13 10:00 ` Borislav Petkov
2021-01-13 16:06 ` Luck, Tony
2021-01-13 16:19 ` Borislav Petkov
2021-01-13 16:32 ` Luck, Tony
2021-01-13 17:35 ` Borislav Petkov
2021-01-14 20:22 ` Borislav Petkov
2021-01-14 21:05 ` Luck, Tony
2021-01-11 21:44 ` [PATCH v2 2/3] x86/mce: Add new return value to get_user() for machine check Tony Luck
2021-01-11 21:44 ` [PATCH v2 3/3] futex, x86/mce: Avoid double machine checks Tony Luck
2021-01-14 17:22 ` [PATCH v2 0/3] Fix infinite machine check loop in futex_wait_setup() Andy Lutomirski
2021-01-15 0:38 ` [PATCH v3] x86/mce: Avoid infinite loop for copy from user recovery Tony Luck
2021-01-15 15:27 ` Borislav Petkov
2021-01-15 19:34 ` Luck, Tony
2021-01-15 20:51 ` [PATCH v4] " Luck, Tony
2021-01-15 23:23 ` Luck, Tony
2021-01-19 10:56 ` Borislav Petkov
2021-01-19 23:57 ` Luck, Tony
2021-01-20 12:18 ` Borislav Petkov
2021-01-20 17:17 ` Luck, Tony
2021-01-21 21:09 ` Luck, Tony
2021-01-25 22:55 ` [PATCH v5] " Luck, Tony
2021-01-26 11:03 ` Borislav Petkov
2021-01-26 22:36 ` Luck, Tony
2021-01-28 17:57 ` Borislav Petkov
2021-02-01 18:58 ` Luck, Tony
2021-02-02 11:01 ` Borislav Petkov
2021-02-02 16:04 ` Luck, Tony
2021-02-02 21:06 ` Borislav Petkov
2021-02-02 22:12 ` Luck, Tony
2021-01-18 15:39 ` [PATCH v3] " Borislav Petkov
2021-07-06 19:06 [PATCH 0/3] More machine check recovery fixes Tony Luck
2021-08-18 0:29 ` [PATCH v2 " Tony Luck
2021-08-18 0:29 ` [PATCH v2 1/3] x86/mce: Avoid infinite loop for copy from user recovery Tony Luck
2021-08-20 17:31 ` Borislav Petkov
2021-08-20 18:59 ` Luck, Tony
2021-08-20 19:27 ` Borislav Petkov
2021-08-20 20:23 ` Luck, Tony
2021-08-21 4:51 ` Tony Luck
2021-08-21 21:51 ` Al Viro
2021-08-22 14:36 ` Borislav Petkov
2021-08-20 20:33 ` Luck, Tony
2021-08-22 14:46 ` Borislav Petkov
2021-08-23 15:24 ` Luck, Tony
2021-09-13 9:24 ` Borislav Petkov
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=38AF04BE-7F39-450F-8C26-879C9934E3D6@amacapital.net \
--to=luto@amacapital.net \
--cc=akpm@linux-foundation.org \
--cc=bp@alien8.de \
--cc=dvhart@infradead.org \
--cc=linux-edac@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=luto@kernel.org \
--cc=peterz@infradead.org \
--cc=tony.luck@intel.com \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).