arm64: Check if GMID_EL1.BS is the same on all CPUs

The GMID_EL1.BS field determines the number of tags accessed by the
LDGM/STGM instructions (EL1 and up), used by the kernel for copying or
zeroing page tags.

Taint the kernel if GMID_EL1.BS differs between CPUs but only of
CONFIG_ARM64_MTE is enabled.
Signed-off-by: NCatalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Suzuki K Poulose <Suzuki.Poulose@arm.com>
Link: https://lore.kernel.org/r/20210526193621.21559-3-catalin.marinas@arm.comSigned-off-by: NWill Deacon <will@kernel.org>

arch/arm64/include/asm/cpu.h

@@ -20,6 +20,7 @@ struct cpuinfo_arm64 {
 	u64		reg_dczid;
 	u64		reg_midr;
 	u64		reg_revidr;
+	u64		reg_gmid;
 
 	u64		reg_id_aa64dfr0;
 	u64		reg_id_aa64dfr1;

arch/arm64/include/asm/cpufeature.h

@@ -619,6 +619,13 @@ static inline bool id_aa64pfr0_sve(u64 pfr0)
 	return val > 0;
 }
 
+static inline bool id_aa64pfr1_mte(u64 pfr1)
+{
+	u32 val = cpuid_feature_extract_unsigned_field(pfr1, ID_AA64PFR1_MTE_SHIFT);
+
+	return val >= ID_AA64PFR1_MTE;
+}
+
 void __init setup_cpu_features(void);
 void check_local_cpu_capabilities(void);
 

arch/arm64/kernel/cpufeature.c

@@ -400,6 +400,11 @@ static const struct arm64_ftr_bits ftr_dczid[] = {
 	ARM64_FTR_END,
 };
 
+static const struct arm64_ftr_bits ftr_gmid[] = {
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, SYS_GMID_EL1_BS_SHIFT, 4, 0),
+	ARM64_FTR_END,
+};
+
 static const struct arm64_ftr_bits ftr_id_isar0[] = {
 	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, ID_ISAR0_DIVIDE_SHIFT, 4, 0),
 	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, ID_ISAR0_DEBUG_SHIFT, 4, 0),
@@ -617,6 +622,9 @@ static const struct __ftr_reg_entry {
 	/* Op1 = 0, CRn = 1, CRm = 2 */
 	ARM64_FTR_REG(SYS_ZCR_EL1, ftr_zcr),
 
+	/* Op1 = 1, CRn = 0, CRm = 0 */
+	ARM64_FTR_REG(SYS_GMID_EL1, ftr_gmid),
+
 	/* Op1 = 3, CRn = 0, CRm = 0 */
 	{ SYS_CTR_EL0, &arm64_ftr_reg_ctrel0 },
 	ARM64_FTR_REG(SYS_DCZID_EL0, ftr_dczid),
@@ -911,6 +919,9 @@ void __init init_cpu_features(struct cpuinfo_arm64 *info)
 		sve_init_vq_map();
 	}
 
+	if (id_aa64pfr1_mte(info->reg_id_aa64pfr1))
+		init_cpu_ftr_reg(SYS_GMID_EL1, info->reg_gmid);
+
 	/*
 	 * Initialize the indirect array of CPU hwcaps capabilities pointers
 	 * before we handle the boot CPU below.
@@ -1134,6 +1145,16 @@ void update_cpu_features(int cpu,
 			sve_update_vq_map();
 	}
 
+	/*
+	 * The kernel uses the LDGM/STGM instructions and the number of tags
+	 * they read/write depends on the GMID_EL1.BS field. Check that the
+	 * value is the same on all CPUs.
+	 */
+	if (IS_ENABLED(CONFIG_ARM64_MTE) &&
+	    id_aa64pfr1_mte(info->reg_id_aa64pfr1))
+		taint |= check_update_ftr_reg(SYS_GMID_EL1, cpu,
+					      info->reg_gmid, boot->reg_gmid);
+
 	/*
 	 * This relies on a sanitised view of the AArch64 ID registers
 	 * (e.g. SYS_ID_AA64PFR0_EL1), so we call it last.

arch/arm64/kernel/cpuinfo.c

@@ -371,6 +371,9 @@ static void __cpuinfo_store_cpu(struct cpuinfo_arm64 *info)
 	info->reg_id_aa64pfr1 = read_cpuid(ID_AA64PFR1_EL1);
 	info->reg_id_aa64zfr0 = read_cpuid(ID_AA64ZFR0_EL1);
 
+	if (id_aa64pfr1_mte(info->reg_id_aa64pfr1))
+		info->reg_gmid = read_cpuid(GMID_EL1);
+
 	/* Update the 32bit ID registers only if AArch32 is implemented */
 	if (id_aa64pfr0_32bit_el0(info->reg_id_aa64pfr0)) {
 		info->reg_id_dfr0 = read_cpuid(ID_DFR0_EL1);