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From: Peter Zijlstra <peterz@infradead.org>
To: Petr Mladek <pmladek@suse.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>,
	x86@kernel.org, linux-kernel@vger.kernel.org,
	rostedt@goodmis.org, mhiramat@kernel.org, bristot@redhat.com,
	jbaron@akamai.com, torvalds@linux-foundation.org,
	tglx@linutronix.de, mingo@kernel.org, namit@vmware.com,
	hpa@zytor.com, luto@kernel.org, ard.biesheuvel@linaro.org,
	jeyu@kernel.org, live-patching@vger.kernel.org
Subject: Re: [PATCH v4 15/16] module: Move where we mark modules RO,X
Date: Fri, 25 Oct 2019 10:43:00 +0200	[thread overview]
Message-ID: <20191025084300.GG4131@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20191025064456.6jjrngm4m3mspaxw@pathway.suse.cz>

On Fri, Oct 25, 2019 at 08:44:56AM +0200, Petr Mladek wrote:
> On Thu 2019-10-24 15:16:34, Peter Zijlstra wrote:
> > On Wed, Oct 23, 2019 at 12:00:25PM -0500, Josh Poimboeuf wrote:
> > 
> > > > This then raises a number of questions:
> > > > 
> > > >  1) why is that RELA (that obviously does not depend on any module)
> > > >     applied so late?
> > > 
> > > Good question.  The 'pv_ops' symbol is exported by the core kernel, so I
> > > can't see any reason why we'd need to apply that rela late.  In theory,
> > > kpatch-build isn't supposed to convert that to a klp rela.  Maybe
> > > something went wrong in the patch creation code.
> > > 
> > > I'm also questioning why we even need to apply the parainstructions
> > > section late.  Maybe we can remove that apply_paravirt() call
> > > altogether, along with .klp.arch.parainstruction sections.
> 
> Hmm, the original bug report against livepatching was actually about
> paravirt ops, see below.

Yes, I found that.

> > > I'm not sure about alternatives, but maybe we can enforce such
> > > limitations with tooling and/or kernel checks.
> > 
> > Right, so on IRC you implied you might have some additional details on
> > how alternatives were affected; did you manage to dig that up?
> 
> I am not sure what Josh had in mind. But the problem with livepatches,
> paravort ops, and alternatives was described in the related patchset, see
> https://lkml.kernel.org/r/1471481911-5003-1-git-send-email-jeyu@redhat.com

Yes, and my complaint there is that that thread is void of useful
content.

> The original bug report is
> https://lkml.kernel.org/r/20160329120518.GA21252@canonical.com

I found the github (*groan*) link in the thread above.

From all that I could only make that the paravirt stuff is just doing it
wrong (see earlier emails, core-kernel RELAs really should be applied at
the time of patch-module load, there's no excuse for them to be delayed
to the .klp.rela. section) at which point paravirt will also magically
work.

But none of that explains why apply_alternatives() is also delayed.

So I'm very tempted to just revert that patchset for doing it all
wrong.

  reply	other threads:[~2019-10-25  8:43 UTC|newest]

Thread overview: 70+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-18  7:35 [PATCH v4 00/16] Rewrite x86/ftrace to use text_poke (and more) Peter Zijlstra
2019-10-18  7:35 ` [PATCH v4 01/16] x86/alternatives: Teach text_poke_bp() to emulate instructions Peter Zijlstra
2019-10-18  7:35 ` [PATCH v4 02/16] x86/alternatives: Update int3_emulate_push() comment Peter Zijlstra
2019-10-18  7:35 ` [PATCH v4 03/16] x86/alternatives,jump_label: Provide better text_poke() batching interface Peter Zijlstra
2019-10-21  8:48   ` Ingo Molnar
2019-10-21  9:21     ` Peter Zijlstra
2019-10-18  7:35 ` [PATCH v4 04/16] x86/alternatives: Add and use text_gen_insn() helper Peter Zijlstra
2019-10-18  7:35 ` [PATCH v4 05/16] x86/ftrace: Use text_poke() Peter Zijlstra
2019-10-18  7:35 ` [PATCH v4 06/16] x86/mm: Remove set_kernel_text_r[ow]() Peter Zijlstra
2019-10-18  7:35 ` [PATCH v4 07/16] x86/alternative: Add text_opcode_size() Peter Zijlstra
2019-10-18  7:35 ` [PATCH v4 08/16] x86/ftrace: Use text_gen_insn() Peter Zijlstra
2019-10-18  7:35 ` [PATCH v4 09/16] x86/alternative: Remove text_poke_loc::len Peter Zijlstra
2019-10-21  8:58   ` Ingo Molnar
2019-10-21  9:02     ` Ingo Molnar
2019-10-18  7:35 ` [PATCH v4 10/16] x86/alternative: Shrink text_poke_loc Peter Zijlstra
2019-10-21  9:01   ` Ingo Molnar
2019-10-21  9:25     ` Peter Zijlstra
2019-10-21  9:33       ` Ingo Molnar
2019-10-18  7:35 ` [PATCH v4 11/16] x86/kprobes: Convert to text-patching.h Peter Zijlstra
2019-10-21 14:57   ` Masami Hiramatsu
2019-10-18  7:35 ` [PATCH v4 12/16] x86/kprobes: Fix ordering Peter Zijlstra
2019-10-22  1:35   ` Masami Hiramatsu
2019-10-22 10:31     ` Peter Zijlstra
2019-10-18  7:35 ` [PATCH v4 13/16] arm/ftrace: Use __patch_text_real() Peter Zijlstra
2019-10-28 16:25   ` Will Deacon
2019-10-28 16:34     ` Peter Zijlstra
2019-10-28 16:35       ` Peter Zijlstra
2019-10-28 16:47       ` Will Deacon
2019-10-28 16:55         ` Peter Zijlstra
2019-10-18  7:35 ` [PATCH v4 14/16] module: Remove set_all_modules_text_*() Peter Zijlstra
2019-10-18  7:35 ` [PATCH v4 15/16] module: Move where we mark modules RO,X Peter Zijlstra
2019-10-21 13:53   ` Josh Poimboeuf
2019-10-21 14:14     ` Peter Zijlstra
2019-10-21 15:34       ` Peter Zijlstra
2019-10-21 15:44         ` Peter Zijlstra
2019-10-21 16:11         ` Peter Zijlstra
2019-10-22 11:31           ` Heiko Carstens
2019-10-22 12:31             ` Peter Zijlstra
2019-10-23 11:48       ` Peter Zijlstra
2019-10-23 15:16         ` Peter Zijlstra
2019-10-23 17:15           ` Josh Poimboeuf
2019-10-24 10:59             ` Peter Zijlstra
2019-10-24 18:31               ` Josh Poimboeuf
2019-10-24 20:33                 ` Peter Zijlstra
2019-10-23 17:00         ` Josh Poimboeuf
2019-10-24 13:16           ` Peter Zijlstra
2019-10-25  6:44             ` Petr Mladek
2019-10-25  8:43               ` Peter Zijlstra [this message]
2019-10-25 10:06                 ` Peter Zijlstra
2019-10-25 13:50                   ` Josh Poimboeuf
2019-10-26  1:17                   ` Josh Poimboeuf
2019-10-28 10:07                     ` Peter Zijlstra
2019-10-28 10:43                     ` Peter Zijlstra
2019-10-25  9:16               ` Peter Zijlstra
2019-10-22  2:21   ` Steven Rostedt
2019-10-22 20:24     ` Peter Zijlstra
2019-10-22 20:40       ` Steven Rostedt
2019-10-23  9:07         ` Peter Zijlstra
2019-10-23 18:52       ` Steven Rostedt
2019-10-24 10:16         ` Peter Zijlstra
2019-10-24 10:18           ` Peter Zijlstra
2019-10-24 15:00           ` Steven Rostedt
2019-10-24 16:43             ` Peter Zijlstra
2019-10-24 18:17               ` Steven Rostedt
2019-10-24 20:24                 ` Peter Zijlstra
2019-10-24 20:28                   ` Steven Rostedt
2019-10-18  7:35 ` [PATCH v4 16/16] ftrace: Merge ftrace_module_{init,enable}() Peter Zijlstra
2019-10-18  8:20   ` Peter Zijlstra
2019-10-21  9:09 ` [PATCH v4 00/16] Rewrite x86/ftrace to use text_poke (and more) Ingo Molnar
2019-10-21 13:38   ` Steven Rostedt

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