arm64/cpufeature: Optionally disable MTE via command-line

MTE support needs to be optionally disabled in runtime
for HW issue workaround, FW development and some
evaluation works on system resource and performance.

This patch makes two changes:
(1) moves init of tag-allocation bits(ATA/ATA0) to
cpu_enable_mte() as not cached in TLB.

(2) allows ID_AA64PFR1_EL1.MTE to be overridden on
its shadow value by giving "arm64.nomte" on cmdline.

When the feature value is off, ATA and TCF will not set
and the related functionalities are accordingly suppressed.

Suggested-by: Catalin Marinas <catalin.marinas@arm.com>
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>
Link: https://lore.kernel.org/r/20210803070824.7586-2-yee.lee@mediatek.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index bdb2200..6f257e3 100644 (file)
--- 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/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
index f6687f6..fc88739 100644 (file)
--- a/arch/arm64/include/asm/sysreg.h
+++ b/arch/arm64/include/asm/sysreg.h
@@ -699,8 +699,7 @@
        (SCTLR_ELx_M    | SCTLR_ELx_C    | SCTLR_ELx_SA   | SCTLR_EL1_SA0   | \
         SCTLR_EL1_SED  | SCTLR_ELx_I    | SCTLR_EL1_DZE  | SCTLR_EL1_UCT   | \
         SCTLR_EL1_NTWE | SCTLR_ELx_IESB | SCTLR_EL1_SPAN | SCTLR_ELx_ITFSB | \
-        SCTLR_ELx_ATA  | SCTLR_EL1_ATA0 | ENDIAN_SET_EL1 | SCTLR_EL1_UCI   | \
-        SCTLR_EL1_EPAN | SCTLR_EL1_RES1)
+        ENDIAN_SET_EL1 | SCTLR_EL1_UCI  | SCTLR_EL1_EPAN | SCTLR_EL1_RES1)
 
 /* MAIR_ELx memory attributes (used by Linux) */
 #define MAIR_ATTR_DEVICE_nGnRnE                UL(0x00)

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 0ead8bf..51e6bf4 100644 (file)
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -1843,6 +1843,9 @@ static void bti_enable(const struct arm64_cpu_capabilities *__unused)
 #ifdef CONFIG_ARM64_MTE
 static void cpu_enable_mte(struct arm64_cpu_capabilities const *cap)
 {
+       sysreg_clear_set(sctlr_el1, 0, SCTLR_ELx_ATA | SCTLR_EL1_ATA0);
+       isb();
+
        /*
         * Clear the tags in the zero page. This needs to be done via the
         * linear map which has the Tagged attribute.

diff --git a/arch/arm64/kernel/idreg-override.c b/arch/arm64/kernel/idreg-override.c
index 53a381a..d8e606f 100644 (file)
--- 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" },
 };