linux-kernel - Re: [PATCH v4 28/39] unwind_user/deferred: Add deferred unwinding interface

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: <20250122215241.gpzay24gzx4yggla@jpoimboe>
Date: Wed, 22 Jan 2025 13:52:41 -0800
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: x86@...nel.org, Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	linux-kernel@...r.kernel.org, Indu Bhagat <indu.bhagat@...cle.com>,
	Mark Rutland <mark.rutland@....com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>, Namhyung Kim <namhyung@...nel.org>,
	Ian Rogers <irogers@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	linux-perf-users@...r.kernel.org, Mark Brown <broonie@...nel.org>,
	linux-toolchains@...r.kernel.org, Jordan Rome <jordalgo@...a.com>,
	Sam James <sam@...too.org>, linux-trace-kernel@...r.kernel.org,
	Andrii Nakryiko <andrii.nakryiko@...il.com>,
	Jens Remus <jremus@...ux.ibm.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Florian Weimer <fweimer@...hat.com>,
	Andy Lutomirski <luto@...nel.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Weinan Liu <wnliu@...gle.com>
Subject: Re: [PATCH v4 28/39] unwind_user/deferred: Add deferred unwinding
 interface

On Wed, Jan 22, 2025 at 02:44:20PM +0100, Peter Zijlstra wrote:
> On Tue, Jan 21, 2025 at 06:31:20PM -0800, Josh Poimboeuf wrote:
> 
> > +/* entry-from-user counter */
> > +static DEFINE_PER_CPU(u64, unwind_ctx_ctr);
> 
> AFAICT from the below, this thing does *not* count entry-from-user. It
> might count a subset, but I need to stare longer.

Right, it's a subset.  Something like so:

/*
 * This is a unique percpu identifier for a given task entry context.
 * Conceptually, it's incremented every time the CPU enters the kernel from
 * user space, so that each "entry context" on the CPU gets a unique ID.  In
 * reality, as an optimization, it's only incremented on demand for the first
 * deferred unwind request after a given entry-from-user.
 *
 * It's combined with the CPU id to make a systemwide-unique "context cookie".
 */
static DEFINE_PER_CPU(u64, unwind_ctx_ctr);

-- 
Josh