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From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Nadav Amit <namit@vmware.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	Andy Lutomirski <luto@kernel.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>,
	Steven Rostedt <rostedt@goodmis.org>,
	Ingo Molnar <mingo@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Masami Hiramatsu <mhiramat@kernel.org>,
	Jason Baron <jbaron@akamai.com>, Jiri Kosina <jkosina@suse.cz>,
	David Laight <David.Laight@aculab.com>,
	Borislav Petkov <bp@alien8.de>, Julia Cartwright <julia@ni.com>,
	Jessica Yu <jeyu@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
	Rasmus Villemoes <linux@rasmusvillemoes.dk>,
	Edward Cree <ecree@solarflare.com>,
	Daniel Bristot de Oliveira <bristot@redhat.com>
Subject: Re: [PATCH v3 0/6] Static calls
Date: Fri, 11 Jan 2019 15:41:22 -0600	[thread overview]
Message-ID: <20190111214122.dzye2mg32aksuyo3@treble> (raw)
In-Reply-To: <6B0B7437-0577-4FE7-A0BC-EFB5D94B8C21@vmware.com>

On Fri, Jan 11, 2019 at 09:36:59PM +0000, Nadav Amit wrote:
> > On Jan 11, 2019, at 1:22 PM, Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> > 
> > On Fri, Jan 11, 2019 at 12:46:39PM -0800, Linus Torvalds wrote:
> >> On Fri, Jan 11, 2019 at 12:31 PM Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> >>> I was referring to the fact that a single static call key update will
> >>> usually result in patching multiple call sites.  But you're right, it's
> >>> only 1-2 trampolines per text_poke_bp() invocation.  Though eventually
> >>> we may want to batch all the writes like what Daniel has proposed for
> >>> jump labels, to reduce IPIs.
> >> 
> >> Yeah, my suggestion doesn't allow for batching, since it would
> >> basically generate one trampoline for every rewritten instruction.
> > 
> > As Andy said, I think batching would still be possible, it's just that
> > we'd have to create multiple trampolines at a time.
> > 
> > Or... we could do a hybrid approach: create a single custom trampoline
> > which has the call destination patched in, but put the return address in
> > %rax -- which is always clobbered, even for callee-saved PV ops.  Like:
> > 
> > trampoline:
> > 	push %rax
> > 	call patched-dest
> > 
> > That way the batching could be done with a single trampoline
> > (particularly if using rcu-sched to avoid the sti hack).
> 
> I don’t see RCU-sched solves the problem if you don’t disable preemption. On
> a fully preemptable kernel, you can get preempted between the push and the
> call (jmp) or before the push. RCU-sched can then finish, and the preempted
> task may later jump to a wrong patched-dest.

Argh, I misspoke about RCU-sched.  Words are hard.

I meant synchronize_rcu_tasks(), which is a completely different animal.
My understanding is that it waits until all runnable tasks (including
preempted tasks) have gotten a chance to run.

-- 
Josh

  reply	other threads:[~2019-01-11 21:41 UTC|newest]

Thread overview: 90+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-01-09 22:59 [PATCH v3 0/6] Static calls Josh Poimboeuf
2019-01-09 22:59 ` [PATCH v3 1/6] compiler.h: Make __ADDRESSABLE() symbol truly unique Josh Poimboeuf
2019-01-09 22:59 ` [PATCH v3 2/6] static_call: Add basic static call infrastructure Josh Poimboeuf
2019-01-10 14:03   ` Edward Cree
2019-01-10 18:37     ` Josh Poimboeuf
2019-01-09 22:59 ` [PATCH v3 3/6] x86/static_call: Add out-of-line static call implementation Josh Poimboeuf
2019-01-10  0:16   ` Nadav Amit
2019-01-10 16:28     ` Josh Poimboeuf
2019-01-09 22:59 ` [PATCH v3 4/6] static_call: Add inline static call infrastructure Josh Poimboeuf
2019-01-09 22:59 ` [PATCH v3 5/6] x86/alternative: Use a single access in text_poke() where possible Josh Poimboeuf
2019-01-10  9:32   ` Nadav Amit
2019-01-10 17:20     ` Josh Poimboeuf
2019-01-10 17:29       ` Nadav Amit
2019-01-10 17:32       ` Steven Rostedt
2019-01-10 17:42         ` Sean Christopherson
2019-01-10 17:57           ` Steven Rostedt
2019-01-10 18:04             ` Sean Christopherson
2019-01-10 18:21               ` Josh Poimboeuf
2019-01-10 18:24               ` Steven Rostedt
2019-01-11 12:10               ` Alexandre Chartre
2019-01-11 15:28                 ` Josh Poimboeuf
2019-01-11 16:46                   ` Alexandre Chartre
2019-01-11 16:57                     ` Josh Poimboeuf
2019-01-11 17:41                       ` Jason Baron
2019-01-11 17:54                         ` Nadav Amit
2019-01-15 11:10                       ` Alexandre Chartre
2019-01-15 16:19                         ` Steven Rostedt
2019-01-15 16:45                           ` Alexandre Chartre
2019-01-11  0:59           ` hpa
2019-01-11  1:34             ` Sean Christopherson
2019-01-11  8:13               ` hpa
2019-01-09 22:59 ` [PATCH v3 6/6] x86/static_call: Add inline static call implementation for x86-64 Josh Poimboeuf
2019-01-10  1:21 ` [PATCH v3 0/6] Static calls Nadav Amit
2019-01-10 16:44   ` Josh Poimboeuf
2019-01-10 17:32     ` Nadav Amit
2019-01-10 18:18       ` Josh Poimboeuf
2019-01-10 19:45         ` Nadav Amit
2019-01-10 20:32           ` Josh Poimboeuf
2019-01-10 20:48             ` Nadav Amit
2019-01-10 20:57               ` Josh Poimboeuf
2019-01-10 21:47                 ` Nadav Amit
2019-01-10 17:31 ` Linus Torvalds
2019-01-10 20:51   ` H. Peter Anvin
2019-01-10 20:30 ` Peter Zijlstra
2019-01-10 20:52   ` Josh Poimboeuf
2019-01-10 23:02     ` Linus Torvalds
2019-01-11  0:56       ` Andy Lutomirski
2019-01-11  1:47         ` Nadav Amit
2019-01-11 15:15           ` Josh Poimboeuf
2019-01-11 15:48             ` Nadav Amit
2019-01-11 16:07               ` Josh Poimboeuf
2019-01-11 17:23                 ` Nadav Amit
2019-01-11 19:03             ` Linus Torvalds
2019-01-11 19:17               ` Nadav Amit
2019-01-11 19:23               ` hpa
2019-01-11 19:33                 ` Nadav Amit
2019-01-11 19:34                 ` Linus Torvalds
2019-01-13  0:34                   ` hpa
2019-01-13  0:36                   ` hpa
2019-01-11 19:39                 ` Jiri Kosina
2019-01-14  2:31                   ` H. Peter Anvin
2019-01-14  2:40                     ` H. Peter Anvin
2019-01-14 20:11                       ` Andy Lutomirski
2019-01-14 22:00                       ` H. Peter Anvin
2019-01-14 22:54                         ` H. Peter Anvin
2019-01-15  3:05                           ` Andy Lutomirski
2019-01-15  5:01                             ` H. Peter Anvin
2019-01-15  5:37                               ` H. Peter Anvin
2019-01-14 23:27                         ` Andy Lutomirski
2019-01-14 23:51                           ` Nadav Amit
2019-01-15  2:28                           ` hpa
2019-01-11 20:04               ` Josh Poimboeuf
2019-01-11 20:12                 ` Linus Torvalds
2019-01-11 20:31                   ` Josh Poimboeuf
2019-01-11 20:46                     ` Linus Torvalds
2019-01-11 21:05                       ` Andy Lutomirski
2019-01-11 21:10                         ` Linus Torvalds
2019-01-11 21:32                           ` Josh Poimboeuf
2019-01-14 12:28                         ` Peter Zijlstra
2019-01-11 21:22                       ` Josh Poimboeuf
2019-01-11 21:23                         ` Josh Poimboeuf
2019-01-11 21:25                         ` Josh Poimboeuf
2019-01-11 21:36                         ` Nadav Amit
2019-01-11 21:41                           ` Josh Poimboeuf [this message]
2019-01-11 21:55                             ` Steven Rostedt
2019-01-11 21:59                               ` Nadav Amit
2019-01-11 21:56                             ` Nadav Amit
2019-01-12 23:54                         ` Andy Lutomirski
2020-02-17 21:10     ` Jann Horn
2020-02-17 21:57       ` Steven Rostedt

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