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

yee.lee
2021-07-30T14:50:37Z

From: Yee Lee <yee.lee@mediatek.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@kernel.org>
Suggested-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Yee Lee <yee.lee@mediatek.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