Re: [PATCH v3 2/7] x86/jump_label: Use text_poke_early() during early_init

From: Peter Zijlstra <peterz@infradead.org>
To: Nadav Amit <namit@vmware.com>
Cc: Ingo Molnar <mingo@redhat.com>,
	LKML <linux-kernel@vger.kernel.org>, X86 ML <x86@kernel.org>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Borislav Petkov <bp@alien8.de>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Andy Lutomirski <luto@kernel.org>,
	Kees Cook <keescook@chromium.org>,
	Dave Hansen <dave.hansen@intel.com>,
	Masami Hiramatsu <mhiramat@kernel.org>
Subject: Re: [PATCH v3 2/7] x86/jump_label: Use text_poke_early() during early_init
Date: Thu, 8 Nov 2018 11:41:41 +0100	[thread overview]
Message-ID: <20181108104141.GR9761@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <9A69025F-5B49-4A26-AB95-F6D36908983B@vmware.com>

On Wed, Nov 07, 2018 at 07:13:03PM +0000, Nadav Amit wrote:
> > diff --git a/arch/x86/kernel/jump_label.c b/arch/x86/kernel/jump_label.c
> > index aac0c1f7e354..ed5fe274a7d8 100644
> > --- a/arch/x86/kernel/jump_label.c
> > +++ b/arch/x86/kernel/jump_label.c
> > @@ -52,7 +52,12 @@ static void __ref __jump_label_transform(struct jump_entry *entry,
> > 	jmp.offset = jump_entry_target(entry) -
> > 		     (jump_entry_code(entry) + JUMP_LABEL_NOP_SIZE);
> > 
> > -	if (early_boot_irqs_disabled)
> > +	/*
> > +	 * As long as we're UP and not yet marked RO, we can use
> > +	 * text_poke_early; SYSTEM_BOOTING guarantees both, as we switch to
> > +	 * SYSTEM_SCHEDULING before going either.
> > +	 */
> > +	if (system_state == SYSTEM_BOOTING)
> > 		poker = text_poke_early;
> > 
> > 	if (type == JUMP_LABEL_JMP) {
> 
> Thanks for this change, I will incorporate it.
> 
> I wanted to point a small difference from my version. Although this version
> ensures we are UP and the kernel is still RW, preemption is possible with
> this version. I presume that it should not affect jump-labels, since it
> switches between JMP and multi-byte NOPs.

Right, we're never running the code we're going to change on UP.