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Date: Thu, 7 Mar 2019 18:06:29 +0100
From: Borislav Petkov <>
Cc: Nadav Amit <>,
	Rick Edgecombe <>,
	Andy Lutomirski <>, Ingo Molnar <>,
	LKML <>, X86 ML <>,
	Thomas Gleixner <>,
	Dave Hansen <>,
	Peter Zijlstra <>,
	Damian Tometzki <>,
	linux-integrity <>,
	LSM List <>,
	Andrew Morton <>,
	Kernel Hardening <>,
	Linux-MM <>, Will Deacon <>,
	Ard Biesheuvel <>,
	Kristen Carlson Accardi <>,
	"Dock, Deneen T" <>,
	Kees Cook <>,
	Dave Hansen <>,
	Masami Hiramatsu <>
Subject: Re: [PATCH v2 10/20] x86: avoid W^X being broken during modules

On Thu, Mar 07, 2019 at 08:53:34AM -0800, wrote:
> If we *do*, what is the issue here? Although boot_cpu_has() isn't
> slow (it should in general be possible to reduce to one testb
> instruction followed by a conditional jump) it seems that "avoiding an
> alternatives slot" *should* be a *very* weak reason, and seems to me
> to look like papering over some other problem.

Forget the current thread: this is simply trying to document when to use
static_cpu_has() and when to use boot_cpu_has(). I get asked about it at
least once a month.

And then it is replacing clear slow paths using static_cpu_has() with
boot_cpu_has() because there's purely no need to patch there. And having
a RIP-relative MOV and a JMP is good enough for slow paths.

Makes sense?


Good mailing practices for 400: avoid top-posting and trim the reply.

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