linux-kernel - [PATCH v3] x86/retbleed: add "stuff" mode admin documentation

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Message-Id: <20230110003101.32212-1-rdunlap@infradead.org>
Date:   Mon,  9 Jan 2023 16:31:01 -0800
From:   Randy Dunlap <rdunlap@...radead.org>
To:     linux-kernel@...r.kernel.org
Cc:     Randy Dunlap <rdunlap@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org,
        Ingo Molnar <mingo@...nel.org>
Subject: [PATCH v3] x86/retbleed: add "stuff" mode admin documentation

Add admin documentation for "retbleed=stuff", based on commit
description and source code.

Fixes: d82a0345cf21 ("x86/retbleed: Add call depth tracking mitigation")
Signed-off-by: Randy Dunlap <rdunlap@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: x86@...nel.org
Cc: Jonathan Corbet <corbet@....net>
Cc: linux-doc@...r.kernel.org
Acked-by: Ingo Molnar <mingo@...nel.org>
---
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/admin-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.