From nobody Mon Sep 15 21:04:21 2025 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5BB9DC67871 for ; Tue, 10 Jan 2023 00:32:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237546AbjAJAcN (ORCPT ); Mon, 9 Jan 2023 19:32:13 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33054 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237634AbjAJAbH (ORCPT ); Mon, 9 Jan 2023 19:31:07 -0500 Received: from bombadil.infradead.org (bombadil.infradead.org [IPv6:2607:7c80:54:3::133]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 647BE6273; Mon, 9 Jan 2023 16:31:03 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20210309; h=Content-Transfer-Encoding: MIME-Version:Message-Id:Date:Subject:Cc:To:From:Sender:Reply-To:Content-Type: Content-ID:Content-Description:In-Reply-To:References; bh=uT+CcmkAN3pOl5VJRzdjuRehxsAaSFf7gHylFoLYXTE=; b=n4cIhIuvpCSTVwvKs1WGrt9jEU 0QX8nIyYmyZkpUjCkLkVpJRTwiKSkjvyAKr9/bFV/VzpU5N5LMHaANvh/jQFIG2/zs60Gsm5xKIof 2Jpdl2PZtYXCmm1bwRkdqORKzb+mebFdHNF86YCMg6fn0J4SpH+E5xzaq3c3YefM9CY5WEXNlD/9h CeIKTFRIkOQ+vcc78FjTRFxSGgM5hdOwJ1Cpj66Ke52Fv8KgMYKpGTVGINoHA6rUfxIB2eZWoiwnn jZoqUwOLnDEe0OYmN2UQHvet5fV2PyAcDgSr8QAIsmwlqkIL6AHmYBsmFVsOmNSpRMa6m96s7ey4W jIHw8Kwg==; Received: from [2601:1c2:d80:3110::a2e7] (helo=bombadil.infradead.org) by bombadil.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1pF2Xe-004lGP-Ht; Tue, 10 Jan 2023 00:31:02 +0000 From: Randy Dunlap To: linux-kernel@vger.kernel.org Cc: Randy Dunlap , Thomas Gleixner , Borislav Petkov , Ingo Molnar , Dave Hansen , x86@kernel.org, Jonathan Corbet , linux-doc@vger.kernel.org, Ingo Molnar Subject: [PATCH v3] x86/retbleed: add "stuff" mode admin documentation Date: Mon, 9 Jan 2023 16:31:01 -0800 Message-Id: <20230110003101.32212-1-rdunlap@infradead.org> X-Mailer: git-send-email 2.39.0 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" Add admin documentation for "retbleed=3Dstuff", based on commit description and source code. Fixes: d82a0345cf21 ("x86/retbleed: Add call depth tracking mitigation") Signed-off-by: Randy Dunlap Cc: Thomas Gleixner Cc: Borislav Petkov Cc: Ingo Molnar Cc: Dave Hansen Cc: x86@kernel.org Cc: Jonathan Corbet Cc: linux-doc@vger.kernel.org Acked-by: Ingo Molnar --- v2: fix typo "if effect" -> "in effect" (thanks Ingo) add Ack from Ingo; v3: change wording of IBRS alternative (thanks Dave H.) Documentation/admin-guide/kernel-parameters.txt | 8 ++++++++ 1 file changed, 8 insertions(+) diff -- a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/a= dmin-guide/kernel-parameters.txt --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -5364,6 +5364,14 @@ when STIBP is not available. This is the alternative for systems which do not have STIBP. + stuff - Enables "stuffing" mode mitigation, + which uses return thunking and call depth + tracking. Only in effect if + CONFIG_CALL_DEPTH_TRACKING is set and + Spectre V2 mitigation mode is + "retpoline". + IBRS is a stronger mitigation but is + more costly (slower) than stuffing. unret - Force enable untrained return thunks, only effective on AMD f15h-f17h based systems.