linux-kernel - Re: [PATCH] x86/alternatives: remove false sharing in poke_int3

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250324113304.GB14944@noisy.programming.kicks-ass.net>
Date: Mon, 24 Mar 2025 12:33:04 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Eric Dumazet <edumazet@...gle.com>
Cc: Ingo Molnar <mingo@...nel.org>, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"H . Peter Anvin" <hpa@...or.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Masami Hiramatsu <mhiramat@...nel.org>, x86@...nel.org,
	bpf@...r.kernel.org, Eric Dumazet <eric.dumazet@...il.com>,
	Greg Thelen <gthelen@...gle.com>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH] x86/alternatives: remove false sharing in
 poke_int3_handler()

On Mon, Mar 24, 2025 at 08:53:31AM +0100, Eric Dumazet wrote:

> BTW the atomic_cond_read_acquire() part is never called even during my
> stress test.

Yes, IIRC this is due to text_poke_sync() serializing the state, as that
does a synchronous IPI broadcast, which by necessity requires all
previous INT3 handlers to complete.

You can only hit that case if the INT3 remains after step-3 (IOW you're
actively writing INT3 into the text). This is exceedingly rare.