linux-kernel - Re: [RFC PATCH v3 11/15] context-tracking: Introduce work deferral infrastructure

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: <Zz2_7MbxvfjKsz08@pavilion.home>
Date: Wed, 20 Nov 2024 11:54:36 +0100
From: Frederic Weisbecker <frederic@...nel.org>
To: Valentin Schneider <vschneid@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
	kvm@...r.kernel.org, linux-mm@...ck.org, bpf@...r.kernel.org,
	x86@...nel.org, rcu@...r.kernel.org,
	linux-kselftest@...r.kernel.org,
	Nicolas Saenz Julienne <nsaenzju@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Jonathan Corbet <corbet@....net>,
	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>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Wanpeng Li <wanpengli@...cent.com>,
	Vitaly Kuznetsov <vkuznets@...hat.com>,
	Andy Lutomirski <luto@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Neeraj Upadhyay <quic_neeraju@...cinc.com>,
	Joel Fernandes <joel@...lfernandes.org>,
	Josh Triplett <josh@...htriplett.org>,
	Boqun Feng <boqun.feng@...il.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Lai Jiangshan <jiangshanlai@...il.com>,
	Zqiang <qiang.zhang1211@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Uladzislau Rezki <urezki@...il.com>,
	Christoph Hellwig <hch@...radead.org>,
	Lorenzo Stoakes <lstoakes@...il.com>,
	Josh Poimboeuf <jpoimboe@...nel.org>,
	Jason Baron <jbaron@...mai.com>, Kees Cook <keescook@...omium.org>,
	Sami Tolvanen <samitolvanen@...gle.com>,
	Ard Biesheuvel <ardb@...nel.org>,
	Nicholas Piggin <npiggin@...il.com>,
	Juerg Haefliger <juerg.haefliger@...onical.com>,
	Nicolas Saenz Julienne <nsaenz@...nel.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Nadav Amit <namit@...are.com>, Dan Carpenter <error27@...il.com>,
	Chuang Wang <nashuiliang@...il.com>,
	Yang Jihong <yangjihong1@...wei.com>,
	Petr Mladek <pmladek@...e.com>,
	"Jason A. Donenfeld" <Jason@...c4.com>, Song Liu <song@...nel.org>,
	Julian Pidancet <julian.pidancet@...cle.com>,
	Tom Lendacky <thomas.lendacky@....com>,
	Dionna Glaze <dionnaglaze@...gle.com>,
	Thomas Weißschuh <linux@...ssschuh.net>,
	Juri Lelli <juri.lelli@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Yair Podemsky <ypodemsk@...hat.com>,
	Daniel Wagner <dwagner@...e.de>, Petr Tesarik <ptesarik@...e.com>
Subject: Re: [RFC PATCH v3 11/15] context-tracking: Introduce work deferral
 infrastructure

Le Tue, Nov 19, 2024 at 04:34:58PM +0100, Valentin Schneider a écrit :
> +bool ct_set_cpu_work(unsigned int cpu, unsigned int work)
> +{
> +	struct context_tracking *ct = per_cpu_ptr(&context_tracking, cpu);
> +	unsigned int old;
> +	bool ret = false;
> +
> +	preempt_disable();
> +
> +	old = atomic_read(&ct->state);
> +	/*
> +	 * Try setting the work until either
> +	 * - the target CPU has entered kernelspace
> +	 * - the work has been set
> +	 */
> +	do {
> +		ret = atomic_try_cmpxchg(&ct->state, &old, old | (work << CT_WORK_START));
> +	} while (!ret && ((old & CT_STATE_MASK) != CT_STATE_KERNEL));
> +
> +	preempt_enable();
> +	return ret;

Does it ignore the IPI even if:

     (ret && (old & CT_STATE_MASK) == CT_STATE_KERNEL))

?

And what about CT_STATE_IDLE?

Is the work ignored in those two cases?

But would it be cleaner to never set the work if the target is elsewhere
than CT_STATE_USER. So you don't need to clear the work on kernel exit
but rather on kernel entry.

That is:

bool ct_set_cpu_work(unsigned int cpu, unsigned int work)
{
	struct context_tracking *ct = per_cpu_ptr(&context_tracking, cpu);
	unsigned int old;
	bool ret = false;

	preempt_disable();

	old = atomic_read(&ct->state);

	/* Start with our best wishes */
	old &= ~CT_STATE_MASK;
	old |= CT_STATE_USER

	/*
	 * Try setting the work until either
	 * - the target CPU has exited userspace
	 * - the work has been set
	 */
	do {
		ret = atomic_try_cmpxchg(&ct->state, &old, old | (work << CT_WORK_START));
	} while (!ret && ((old & CT_STATE_MASK) == CT_STATE_USER));

	preempt_enable();

	return ret;
}

Thanks.