From: Nadav Amit <namit@vmware.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
LKML <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@redhat.com>, X86 ML <x86@kernel.org>,
Arnd Bergmann <arnd@arndb.de>,
linux-arch <linux-arch@vger.kernel.org>,
Dave Hansen <dave.hansen@linux.intel.com>,
Jiri Kosina <jkosina@suse.cz>, Andy Lutomirski <luto@kernel.org>,
Kees Cook <keescook@chromium.org>,
Dave Hansen <dave.hansen@intel.com>
Subject: Re: [PATCH v2 1/6] Fix "x86/alternatives: Lockdep-enforce text_mutex in text_poke*()"
Date: Thu, 6 Sep 2018 19:58:40 +0000 [thread overview]
Message-ID: <D8CE0D88-9507-421C-9C97-ACAB05388F8D@vmware.com> (raw)
In-Reply-To: <20180906195351.GB9358@worktop.programming.kicks-ass.net>
at 12:53 PM, Peter Zijlstra <peterz@infradead.org> wrote:
> On Thu, Sep 06, 2018 at 07:42:14PM +0000, Nadav Amit wrote:
>> at 12:40 PM, Peter Zijlstra <peterz@infradead.org> wrote:
>>
>>> On Sun, Sep 02, 2018 at 10:32:19AM -0700, Nadav Amit wrote:
>>>> text_mutex is expected to be held before text_poke() is called, but we
>>>> cannot add a lockdep assertion since kgdb does not take it, and instead
>>>> *supposedly* ensures the lock is not taken and will not be acquired by
>>>> any other core while text_poke() is running.
>>>>
>>>> The reason for the "supposedly" comment is that it is not entirely clear
>>>> that this would be the case if gdb_do_roundup is zero.
>>>
>>> Argh, that's pretty shit code...
>>>
>>> Not only is that text_mutex abuse ugly, so too is the fixmap usage from
>>> IRQ context. I suppose this really does require your alternative mm
>>> patches for text_poke().
>>
>> Right, I forgot about that…
>
> With that CR3 trickery, we can rid ourselves of the text_mutex
> requirement, since concurrent text_poke is 'safe'. That would clean up
> the kgdb code quite a bit.
I don’t know. I’m somewhat worried with multiple mechanisms potentially
changing the same code at the same time - and maybe ending up with some
mess.
next prev parent reply other threads:[~2018-09-06 19:58 UTC|newest]
Thread overview: 62+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-02 17:32 [PATCH v2 0/6] x86/alternatives: text_poke() fixes Nadav Amit
2018-09-02 17:32 ` Nadav Amit
2018-09-02 17:32 ` [PATCH v2 1/6] Fix "x86/alternatives: Lockdep-enforce text_mutex in text_poke*()" Nadav Amit
2018-09-02 17:32 ` Nadav Amit
2018-09-06 19:40 ` Peter Zijlstra
2018-09-06 19:40 ` Peter Zijlstra
2018-09-06 19:42 ` Nadav Amit
2018-09-06 19:42 ` Nadav Amit
2018-09-06 19:53 ` Peter Zijlstra
2018-09-06 19:53 ` Peter Zijlstra
2018-09-06 19:58 ` Nadav Amit [this message]
2018-09-06 19:58 ` Nadav Amit
2018-09-06 20:25 ` Peter Zijlstra
2018-09-06 20:25 ` Peter Zijlstra
2018-09-06 20:57 ` Nadav Amit
2018-09-06 20:57 ` Nadav Amit
2018-09-06 21:41 ` Peter Zijlstra
2018-09-06 21:41 ` Peter Zijlstra
2018-09-02 17:32 ` [PATCH v2 2/6] x86/mm: temporary mm struct Nadav Amit
2018-09-02 17:32 ` Nadav Amit
2018-09-02 17:32 ` [PATCH v2 3/6] fork: provide a function for copying init_mm Nadav Amit
2018-09-02 17:32 ` Nadav Amit
2018-09-02 17:32 ` [PATCH v2 4/6] x86/alternatives: initializing temporary mm for patching Nadav Amit
2018-09-02 17:32 ` Nadav Amit
2018-09-06 9:01 ` Peter Zijlstra
2018-09-06 9:01 ` Peter Zijlstra
2018-09-07 20:52 ` Nadav Amit
2018-09-07 20:52 ` Nadav Amit
2018-09-02 17:32 ` [PATCH v2 5/6] x86/alternatives: use temporary mm for text poking Nadav Amit
2018-09-02 17:32 ` Nadav Amit
2018-09-02 17:32 ` [PATCH v2 6/6] x86/alternatives: remove text_poke() return value Nadav Amit
2018-09-02 17:32 ` Nadav Amit
2018-09-05 18:56 ` [PATCH v2 0/6] x86/alternatives: text_poke() fixes Peter Zijlstra
2018-09-05 18:56 ` Peter Zijlstra
2018-09-05 19:02 ` Nadav Amit
2018-09-05 19:02 ` Nadav Amit
2018-09-05 19:10 ` Nadav Amit
2018-09-05 19:10 ` Nadav Amit
2018-09-06 8:13 ` Peter Zijlstra
2018-09-06 8:13 ` Peter Zijlstra
2018-09-06 8:42 ` Peter Zijlstra
2018-09-06 8:42 ` Peter Zijlstra
2018-09-06 9:18 ` Peter Zijlstra
2018-09-06 9:18 ` Peter Zijlstra
2018-09-06 10:16 ` Peter Zijlstra
2018-09-06 10:16 ` Peter Zijlstra
2018-09-06 17:01 ` Nadav Amit
2018-09-06 17:01 ` Nadav Amit
2018-09-06 17:17 ` Peter Zijlstra
2018-09-06 17:17 ` Peter Zijlstra
2018-09-06 17:58 ` Nadav Amit
2018-09-06 17:58 ` Nadav Amit
2018-09-06 18:09 ` Andy Lutomirski
2018-09-06 18:09 ` Andy Lutomirski
2018-09-06 18:31 ` Peter Zijlstra
2018-09-06 18:31 ` Peter Zijlstra
2018-09-06 18:38 ` Nadav Amit
2018-09-06 18:38 ` Nadav Amit
2018-09-06 19:19 ` Peter Zijlstra
2018-09-06 19:19 ` Peter Zijlstra
2018-09-06 17:23 ` Peter Zijlstra
2018-09-06 17:23 ` Peter Zijlstra
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