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From: Nadav Amit <nadav.amit@gmail.com>
To: Andi Kleen <ak@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Adrian Hunter <adrian.hunter@intel.com>,
	Ingo Molnar <mingo@redhat.com>, Andy Lutomirski <luto@kernel.org>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	Edward Cree <ecree@solarflare.com>,
	"H . Peter Anvin" <hpa@zytor.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	LKML <linux-kernel@vger.kernel.org>, X86 ML <x86@kernel.org>,
	Paolo Abeni <pabeni@redhat.com>, Borislav Petkov <bp@alien8.de>,
	David Woodhouse <dwmw@amazon.co.uk>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	songliubraving@fb.com
Subject: Re: [RFC v2 0/6] x86: dynamic indirect branch promotion
Date: Tue, 8 Jan 2019 10:28:02 -0800
Message-ID: <D1A153D5-D23B-45E6-9E7A-EB9CBAE84B7E@gmail.com> (raw)
In-Reply-To: <20190108172721.GN6118@tassilo.jf.intel.com>

> On Jan 8, 2019, at 9:27 AM, Andi Kleen <ak@linux.intel.com> wrote:
> 
> On Tue, Jan 08, 2019 at 11:10:58AM +0100, Peter Zijlstra wrote:
>> On Tue, Jan 08, 2019 at 12:01:11PM +0200, Adrian Hunter wrote:
>>> The problem is that the jitted code gets freed from memory, which is why I
>>> suggested the ability to pin it for a while.
>> 
>> Then what do you tell the guy that keeps PT running for a day and runs
>> out of memory because he likes to JIT a lot?
> 
> It only would need to be saved until the next kcore dump, so they would
> need to do regular kcore dumps, after each of which the JIT code could be freed.
> 
> In a sense it would be like RCU for code.
> 
> You would somehow need to tell the kernel when that happens though
> so it can schedule the frees.
> 
> It doesn't work when the code is modified in place, like the
> patch in the $SUBJECT.

Excuse my ignorance - can you be more concrete what will break where?

I am looking at perf-with-kcore, and intuitively the main thing that is
required is to take text_mutex while kcore is copied, to get a point-in-time
snapshot.

Is it really that important for debugging to get the instructions at the
time of execution? Wouldn’t it be easier to annotate the instructions that
might change? After all, it is not as if any instruction can change to any
other instruction.


  reply index

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-12-31  7:21 Nadav Amit
2018-12-31  7:21 ` [RFC v2 1/6] x86: introduce kernel restartable sequence Nadav Amit
2018-12-31 20:08   ` Andy Lutomirski
2018-12-31 21:12     ` Nadav Amit
2019-01-03 22:21   ` Andi Kleen
2019-01-03 22:29     ` Nadav Amit
2019-01-03 22:48       ` Andi Kleen
2019-01-03 22:52         ` Nadav Amit
2019-01-03 23:40           ` Andi Kleen
2019-01-03 23:56             ` Nadav Amit
2019-01-04  0:34   ` hpa
2018-12-31  7:21 ` [RFC v2 2/6] objtool: ignore instructions Nadav Amit
2018-12-31  7:21 ` [RFC v2 3/6] x86: patch indirect branch promotion Nadav Amit
2018-12-31  7:21 ` [RFC v2 4/6] x86: interface for accessing indirect branch locations Nadav Amit
2018-12-31  7:21 ` [RFC v2 5/6] x86: learning and patching indirect branch targets Nadav Amit
2018-12-31 20:05   ` Andy Lutomirski
2018-12-31 21:07     ` Nadav Amit
2018-12-31  7:21 ` [RFC v2 6/6] x86: outline optpoline Nadav Amit
2018-12-31 19:51 ` [RFC v2 0/6] x86: dynamic indirect branch promotion Andy Lutomirski
2018-12-31 19:53   ` Nadav Amit
2019-01-03 18:10     ` Josh Poimboeuf
2019-01-03 18:30       ` Nadav Amit
2019-01-03 20:31         ` Josh Poimboeuf
2019-01-03 22:18 ` Andi Kleen
2019-01-07 16:32   ` Peter Zijlstra
2019-01-08  7:47     ` Adrian Hunter
2019-01-08  9:25       ` Peter Zijlstra
2019-01-08 10:01         ` Adrian Hunter
2019-01-08 10:10           ` Peter Zijlstra
2019-01-08 17:27             ` Andi Kleen
2019-01-08 18:28               ` Nadav Amit [this message]
2019-01-08 19:01                 ` Peter Zijlstra
2019-01-08 20:47                   ` Nadav Amit
2019-01-08 20:53                     ` Andi Kleen
2019-01-09 10:35                     ` Peter Zijlstra
2019-08-29  8:23                       ` Tracing text poke / kernel self-modifying code (Was: Re: [RFC v2 0/6] x86: dynamic indirect branch promotion) Adrian Hunter
2019-08-29  8:53                         ` Peter Zijlstra
2019-08-29  9:40                           ` Adrian Hunter
2019-08-29 11:46                             ` Peter Zijlstra
2019-09-12  7:00                               ` Adrian Hunter
2019-09-12 12:17                                 ` hpa
2019-01-08 18:57               ` [RFC v2 0/6] x86: dynamic indirect branch promotion Peter Zijlstra

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