linux-kernel - Re: [PATCH] x86: static_cpu_has_safe: discard dynamic check after init

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Date:	Wed, 20 Jan 2016 11:50:18 +0100
From:	Borislav Petkov <bp@...e.de>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Brian Gerst <brgerst@...il.com>,
	the arch/x86 maintainers <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Andy Lutomirski <luto@...capital.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] x86: static_cpu_has_safe: discard dynamic check after
 init

On Tue, Jan 19, 2016 at 08:42:10PM -0800, H. Peter Anvin wrote:
> Right.  I wish we could tag reference call sites as clean, not sources
> or targets.  Sigh.

I was thinking about something like this:

From: Borislav Petkov <bp@...e.de>
Date: Wed, 20 Jan 2016 11:45:36 +0100
Subject: [PATCH] x86/alternatives: Add an auxilary section

Add .altinstr_aux for additional instructions which will be used before
and/or during patching. All stuff which needs more sophisticated
patching should go there. See next patch.

Signed-off-by: Borislav Petkov <bp@...e.de>
---
 arch/x86/kernel/vmlinux.lds.S | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 74e4bf11f562..35868bf529b9 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -244,6 +244,11 @@ SECTIONS
 	 */
 	.altinstr_replacement : AT(ADDR(.altinstr_replacement) - LOAD_OFFSET) {
 		*(.altinstr_replacement)
+		/*
+		 * Auxiliary section for misc instruction patching tasks. See
+		 * static_cpu_has(), for an example.
+		 */
+		*(.altinstr_aux)
 	}
 
 	/*
-- 
2.3.5

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
--