arm64/mte: Add hwcap for asymmetric mode

Allow userspace to detect support for asymmetric mode by providing a hwcap
for it, using the official feature name FEAT_MTE3.
Signed-off-by: NMark Brown <broonie@kernel.org>
Reviewed-by: NCatalin Marinas <catalin.marinas@arm.com>
Reviewed-by: NVincenzo Frascino <Vincenzo.Frascino@arm.com>
Tested-by: NBranislav Rankov <branislav.rankov@arm.com>
Link: https://lore.kernel.org/r/20220216173224.2342152-4-broonie@kernel.orgSigned-off-by: NWill Deacon <will@kernel.org>

Documentation/arm64/elf_hwcaps.rst

@@ -259,6 +259,11 @@ HWCAP2_RPRES
 
     Functionality implied by ID_AA64ISAR2_EL1.RPRES == 0b0001.
 
+HWCAP2_MTE3
+
+    Functionality implied by ID_AA64PFR1_EL1.MTE == 0b0011, as described
+    by Documentation/arm64/memory-tagging-extension.rst.
+
 4. Unused AT_HWCAP bits
 -----------------------
 

arch/arm64/include/asm/hwcap.h

@@ -108,6 +108,7 @@
 #define KERNEL_HWCAP_ECV		__khwcap2_feature(ECV)
 #define KERNEL_HWCAP_AFP		__khwcap2_feature(AFP)
 #define KERNEL_HWCAP_RPRES		__khwcap2_feature(RPRES)
+#define KERNEL_HWCAP_MTE3		__khwcap2_feature(MTE3)
 
 /*
  * This yields a mask that user programs can use to figure out what

arch/arm64/include/uapi/asm/hwcap.h

@@ -78,5 +78,6 @@
 #define HWCAP2_ECV		(1 << 19)
 #define HWCAP2_AFP		(1 << 20)
 #define HWCAP2_RPRES		(1 << 21)
+#define HWCAP2_MTE3		(1 << 22)
 
 #endif /* _UAPI__ASM_HWCAP_H */

arch/arm64/kernel/cpufeature.c

@@ -2488,6 +2488,7 @@ static const struct arm64_cpu_capabilities arm64_elf_hwcaps[] = {
 #endif
 #ifdef CONFIG_ARM64_MTE
 	HWCAP_CAP(SYS_ID_AA64PFR1_EL1, ID_AA64PFR1_MTE_SHIFT, FTR_UNSIGNED, ID_AA64PFR1_MTE, CAP_HWCAP, KERNEL_HWCAP_MTE),
+	HWCAP_CAP(SYS_ID_AA64PFR1_EL1, ID_AA64PFR1_MTE_SHIFT, FTR_UNSIGNED, ID_AA64PFR1_MTE_ASYMM, CAP_HWCAP, KERNEL_HWCAP_MTE3),
 #endif /* CONFIG_ARM64_MTE */
 	HWCAP_CAP(SYS_ID_AA64MMFR0_EL1, ID_AA64MMFR0_ECV_SHIFT, FTR_UNSIGNED, 1, CAP_HWCAP, KERNEL_HWCAP_ECV),
 	HWCAP_CAP(SYS_ID_AA64MMFR1_EL1, ID_AA64MMFR1_AFP_SHIFT, FTR_UNSIGNED, 1, CAP_HWCAP, KERNEL_HWCAP_AFP),

arch/arm64/kernel/cpuinfo.c

@@ -97,6 +97,7 @@ static const char *const hwcap_str[] = {
 	[KERNEL_HWCAP_ECV]		= "ecv",
 	[KERNEL_HWCAP_AFP]		= "afp",
 	[KERNEL_HWCAP_RPRES]		= "rpres",
+	[KERNEL_HWCAP_MTE3]		= "mte3",
 };
 
 #ifdef CONFIG_COMPAT