linux-kernel - [PATCH v3 1/1] arm64/cpufeature: Optionally disable MTE via command-line

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Date:   Fri, 30 Jul 2021 22:49:53 +0800
From:   <yee.lee@...iatek.com>
To:     <linux-kernel@...r.kernel.org>
CC:     <nicholas.Tang@...iatek.com>, <Kuan-Ying.lee@...iatek.com>,
        <chinwen.chang@...iatek.com>, Yee Lee <yee.lee@...iatek.com>,
        Jonathan Corbet <corbet@....net>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Maciej W. Rozycki" <macro@...am.me.uk>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Marc Zyngier <maz@...nel.org>,
        David Brazdil <dbrazdil@...gle.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Fuad Tabba <tabba@...gle.com>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        "moderated list:ARM64 PORT (AARCH64 ARCHITECTURE)" 
        <linux-arm-kernel@...ts.infradead.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>
Subject: [PATCH v3 1/1] arm64/cpufeature: Optionally disable MTE via command-line

From: Yee Lee <yee.lee@...iatek.com>

For some low-end devices with limited resources,
MTE needs to be optionally disabled to save system
costs such as tag memory and firmware controls.

This allows ID_AA64PFR1_EL1.MTE to be overridden on 
its shadow value by giving "arm64.nomte" on cmdline,
and to suppress MTE feature.

Suggested-by: Marc Zyngier <maz@...nel.org>
Suggested-by: Suzuki K Poulose <suzuki.poulose@....com>
Signed-off-by: Yee Lee <yee.lee@...iatek.com>
---
 Documentation/admin-guide/kernel-parameters.txt | 3 +++
 arch/arm64/kernel/idreg-override.c              | 2 ++
 2 files changed, 5 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index bdb22006f713..6f257e39d89e 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -380,6 +380,9 @@
 	arm64.nopauth	[ARM64] Unconditionally disable Pointer Authentication
 			support
 
+	arm64.nomte	[ARM64] Unconditionally disable Memory Tagging Extension
+			support
+
 	ataflop=	[HW,M68k]
 
 	atarimouse=	[HW,MOUSE] Atari Mouse
diff --git a/arch/arm64/kernel/idreg-override.c b/arch/arm64/kernel/idreg-override.c
index 53a381a7f65d..d8e606fe3c21 100644
--- a/arch/arm64/kernel/idreg-override.c
+++ b/arch/arm64/kernel/idreg-override.c
@@ -54,6 +54,7 @@ static const struct ftr_set_desc pfr1 __initconst = {
 	.override	= &id_aa64pfr1_override,
 	.fields		= {
 	        { "bt", ID_AA64PFR1_BT_SHIFT },
+		{ "mte", ID_AA64PFR1_MTE_SHIFT},
 		{}
 	},
 };
@@ -100,6 +101,7 @@ static const struct {
 	{ "arm64.nopauth",
 	  "id_aa64isar1.gpi=0 id_aa64isar1.gpa=0 "
 	  "id_aa64isar1.api=0 id_aa64isar1.apa=0"	   },
+	{ "arm64.nomte",		"id_aa64pfr1.mte=0" },
 	{ "nokaslr",			"kaslr.disabled=1" },
 };
 
-- 
2.18.0