From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Lutomirski <luto@kernel.org>,
Steven Rostedt <rostedt@goodmis.org>,
Peter Zijlstra <peterz@infradead.org>,
the arch/x86 maintainers <x86@kernel.org>,
Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
Ard Biesheuvel <ard.biesheuvel@linaro.org>,
Ingo Molnar <mingo@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
mhiramat@kernel.org, jbaron@akamai.com,
Jiri Kosina <jkosina@suse.cz>,
David.Laight@aculab.com, bp@alien8.de, julia@ni.com,
jeyu@kernel.org, Peter Anvin <hpa@zytor.com>
Subject: Re: [PATCH v2 4/4] x86/static_call: Add inline static call implementation for x86-64
Date: Fri, 30 Nov 2018 10:27:13 -0600 [thread overview]
Message-ID: <20181130162713.uoeyfau66buntyse@treble> (raw)
In-Reply-To: <CAHk-=wiO87jDPP8FZ7EfwfbFNQRdr64Pa+g33do7tKiTFYz8BA@mail.gmail.com>
On Thu, Nov 29, 2018 at 03:04:20PM -0800, Linus Torvalds wrote:
> On Thu, Nov 29, 2018 at 12:25 PM Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> >
> > On Thu, Nov 29, 2018 at 11:27:00AM -0800, Andy Lutomirski wrote:
> > >
> > > I propose a different solution:
> > >
> > > As in this patch set, we have a direct and an indirect version. The
> > > indirect version remains exactly the same as in this patch set. The
> > > direct version just only does the patching when all seems well: the
> > > call instruction needs to be 0xe8, and we only do it when the thing
> > > doesn't cross a cache line. Does that work? In the rare case where
> > > the compiler generates something other than 0xe8 or crosses a cache
> > > line, then the thing just remains as a call to the out of line jmp
> > > trampoline. Does that seem reasonable? It's a very minor change to
> > > the patch set.
> >
> > Maybe that would be ok. If my math is right, we would use the
> > out-of-line version almost 5% of the time due to cache misalignment of
> > the address.
>
> Note that I don't think cache-line alignment is necessarily sufficient.
>
> The I$ fetch from the cacheline can happen in smaller chunks, because
> the bus between the I$ and the instruction decode isn't a full
> cacheline (well, it is _now_ in modern big cores, but it hasn't always
> been).
>
> So even if the cacheline is updated atomically, I could imagine seeing
> a partial fetch from the I$ (old values) and then a second partial
> fetch (new values).
>
> It would be interesting to know what the exact fetch rules are.
I've been doing some cross-modifying code experiments on Nehalem, with
one CPU writing call destinations while the other CPUs are executing
them. Reliably, one of the readers goes off into the weeds within a few
seconds.
The writing was done with just text_poke(), no #BP.
I wasn't able to figure out the pattern in the addresses of the
corrupted call sites. It wasn't cache line.
That was on Nehalem. Skylake didn't crash at all.
--
Josh
next prev parent reply other threads:[~2018-11-30 16:27 UTC|newest]
Thread overview: 120+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-26 13:54 [PATCH v2 0/4] Static calls Josh Poimboeuf
2018-11-26 13:54 ` [PATCH v2 1/4] compiler.h: Make __ADDRESSABLE() symbol truly unique Josh Poimboeuf
2018-11-27 8:49 ` Ard Biesheuvel
2018-11-26 13:54 ` [PATCH v2 2/4] static_call: Add static call infrastructure Josh Poimboeuf
2018-11-26 13:54 ` [PATCH v2 3/4] x86/static_call: Add out-of-line static call implementation Josh Poimboeuf
2018-11-26 15:43 ` Peter Zijlstra
2018-11-26 16:19 ` Steven Rostedt
2018-11-26 13:55 ` [PATCH v2 4/4] x86/static_call: Add inline static call implementation for x86-64 Josh Poimboeuf
2018-11-26 16:02 ` Peter Zijlstra
2018-11-26 17:10 ` Josh Poimboeuf
2018-11-26 17:56 ` Josh Poimboeuf
2018-11-26 20:00 ` Peter Zijlstra
2018-11-26 20:08 ` Peter Zijlstra
2018-11-26 21:26 ` Josh Poimboeuf
2018-11-27 8:43 ` Peter Zijlstra
2018-11-27 8:50 ` Peter Zijlstra
2018-11-29 6:05 ` Andy Lutomirski
2018-11-29 9:42 ` Peter Zijlstra
2018-11-29 13:11 ` Josh Poimboeuf
2018-11-29 13:37 ` Andy Lutomirski
2018-11-29 14:38 ` Peter Zijlstra
2018-11-29 14:42 ` Jiri Kosina
2018-11-29 16:33 ` Josh Poimboeuf
2018-11-29 16:49 ` Peter Zijlstra
2018-11-29 16:59 ` Andy Lutomirski
2018-11-29 17:10 ` Josh Poimboeuf
2018-11-29 22:01 ` Peter Zijlstra
2018-11-29 22:14 ` Josh Poimboeuf
2018-11-29 22:22 ` Peter Zijlstra
2018-11-29 22:25 ` Andy Lutomirski
2018-11-29 22:30 ` Josh Poimboeuf
2018-11-29 17:15 ` Peter Zijlstra
2018-11-29 17:20 ` Steven Rostedt
2018-11-29 17:21 ` Steven Rostedt
2018-11-29 17:41 ` Andy Lutomirski
2018-11-29 17:45 ` Josh Poimboeuf
2018-11-29 17:52 ` Andy Lutomirski
2018-11-29 17:49 ` Steven Rostedt
2018-11-29 18:37 ` Josh Poimboeuf
2018-11-29 16:50 ` Linus Torvalds
2018-11-29 16:55 ` Steven Rostedt
2018-11-29 17:02 ` Andy Lutomirski
2018-11-29 17:07 ` Peter Zijlstra
2018-11-29 17:31 ` Andy Lutomirski
2018-11-29 17:35 ` Jiri Kosina
2018-11-29 17:13 ` Steven Rostedt
2018-11-29 17:35 ` Linus Torvalds
2018-11-29 17:44 ` Steven Rostedt
2018-11-29 17:50 ` Linus Torvalds
2018-11-29 17:54 ` Linus Torvalds
2018-11-29 17:58 ` Steven Rostedt
2018-11-29 18:23 ` Linus Torvalds
2018-11-29 18:47 ` Steven Rostedt
2018-11-29 18:58 ` Linus Torvalds
2018-11-29 19:08 ` Linus Torvalds
2018-11-29 19:11 ` Linus Torvalds
2018-12-10 23:58 ` Pavel Machek
2018-12-11 1:43 ` Linus Torvalds
2018-11-29 19:12 ` Steven Rostedt
2018-11-29 19:27 ` Andy Lutomirski
2018-11-29 20:24 ` Josh Poimboeuf
2018-11-29 22:17 ` Josh Poimboeuf
2018-11-29 23:04 ` Linus Torvalds
2018-11-30 16:27 ` Josh Poimboeuf [this message]
2018-12-11 9:41 ` David Laight
2018-12-11 17:19 ` Josh Poimboeuf
2018-12-12 18:29 ` Josh Poimboeuf
2018-11-30 16:42 ` Andy Lutomirski
2018-11-30 18:39 ` Josh Poimboeuf
2018-11-30 19:45 ` Linus Torvalds
2018-11-30 20:18 ` Andy Lutomirski
2018-11-30 20:28 ` Steven Rostedt
2018-11-30 20:59 ` Andy Lutomirski
2018-11-30 21:01 ` Steven Rostedt
2018-11-30 21:13 ` Jiri Kosina
2018-11-30 21:10 ` Josh Poimboeuf
2018-11-29 19:16 ` Steven Rostedt
2018-11-29 19:22 ` Josh Poimboeuf
2018-11-29 19:27 ` Steven Rostedt
2018-11-30 22:16 ` Rasmus Villemoes
2018-11-30 22:24 ` Josh Poimboeuf
2018-11-29 19:24 ` Linus Torvalds
2018-11-29 19:28 ` Andy Lutomirski
2018-11-29 19:31 ` Steven Rostedt
2018-11-29 20:12 ` Josh Poimboeuf
2018-11-29 18:00 ` Andy Lutomirski
2018-11-29 18:42 ` Linus Torvalds
2018-11-29 18:55 ` Steven Rostedt
2018-11-29 17:29 ` Linus Torvalds
2018-11-29 17:35 ` Andy Lutomirski
2018-11-26 18:28 ` Andy Lutomirski
2018-11-26 20:14 ` Josh Poimboeuf
2018-11-27 8:46 ` Peter Zijlstra
2018-11-26 16:08 ` Peter Zijlstra
2018-11-26 16:11 ` Ard Biesheuvel
2018-11-26 16:33 ` Andy Lutomirski
2018-11-26 16:39 ` Peter Zijlstra
2018-11-26 16:44 ` Josh Poimboeuf
2018-11-26 14:01 ` [PATCH v2 0/4] Static calls Josh Poimboeuf
2018-11-26 20:54 ` Steven Rostedt
2018-11-26 22:24 ` Josh Poimboeuf
2018-11-26 22:53 ` Steven Rostedt
2018-12-04 23:08 ` Steven Rostedt
2018-12-04 23:41 ` Andy Lutomirski
2018-12-05 15:04 ` Josh Poimboeuf
2018-12-05 23:36 ` Andy Lutomirski
2018-12-07 16:06 ` Edward Cree
2018-12-07 16:49 ` Edward Cree
2018-12-11 18:05 ` Josh Poimboeuf
2018-12-12 5:59 ` Nadav Amit
2018-12-12 17:11 ` Edward Cree
2018-12-12 17:47 ` [RFC/WIP PATCH 0/2] dynamic calls Edward Cree
2018-12-12 17:50 ` [RFC PATCH 1/2] static_call: fix out-of-line static call implementation Edward Cree
2018-12-12 17:52 ` [RFC PATCH 2/2] net: core: rather hacky PoC implementation of dynamic calls Edward Cree
2018-12-12 18:14 ` [PATCH v2 0/4] Static calls Nadav Amit
2018-12-12 18:33 ` Edward Cree
2018-12-12 21:15 ` Nadav Amit
2018-12-12 21:36 ` Edward Cree
2018-12-12 21:45 ` Nadav Amit
2018-12-10 23:57 ` Pavel Machek
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