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.

Signed-off-by: Catalin 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>
---
 arch/arm64/include/asm/cpu.h   |  1 +
 arch/arm64/kernel/cpufeature.c | 17 +++++++++++++++++
 arch/arm64/kernel/cpuinfo.c    |  1 +
 3 files changed, 19 insertions(+)

diff --git a/arch/arm64/include/asm/cpu.h b/arch/arm64/include/asm/cpu.h
index fe5a8499ddc2..9088e72c7cf6 100644
--- a/arch/arm64/include/asm/cpu.h
+++ b/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;

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index ca66a61bb396..3b9089ca52dc 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c

@@ -401,6 +401,11 @@ 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),

@@ -618,6 +623,9 @@ 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),

@@ -872,6 +880,7 @@ void __init init_cpu_features(struct cpuinfo_arm64 *info)
 	init_cpu_ftr_reg(SYS_CTR_EL0, info->reg_ctr);
 	init_cpu_ftr_reg(SYS_DCZID_EL0, info->reg_dczid);
 	init_cpu_ftr_reg(SYS_CNTFRQ_EL0, info->reg_cntfrq);
+	init_cpu_ftr_reg(SYS_GMID_EL1, info->reg_gmid);
 	init_cpu_ftr_reg(SYS_ID_AA64DFR0_EL1, info->reg_id_aa64dfr0);
 	init_cpu_ftr_reg(SYS_ID_AA64DFR1_EL1, info->reg_id_aa64dfr1);
 	init_cpu_ftr_reg(SYS_ID_AA64ISAR0_EL1, info->reg_id_aa64isar0);

@@ -1082,6 +1091,14 @@ void update_cpu_features(int cpu,
 	taint |= check_update_ftr_reg(SYS_DCZID_EL0, cpu,
 				      info->reg_dczid, boot->reg_dczid);
 
+	/*
+	 * 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.
+	 */
+	taint |= check_update_ftr_reg(SYS_GMID_EL1, cpu,
+				      info->reg_gmid, boot->reg_gmid);
+
 	/* If different, timekeeping will be broken (especially with KVM) */
 	taint |= check_update_ftr_reg(SYS_CNTFRQ_EL0, cpu,
 				      info->reg_cntfrq, boot->reg_cntfrq);

diff --git a/arch/arm64/kernel/cpuinfo.c b/arch/arm64/kernel/cpuinfo.c
index 4bea701117d4..cd9f2d51285b 100644
--- a/arch/arm64/kernel/cpuinfo.c
+++ b/arch/arm64/kernel/cpuinfo.c

@@ -359,6 +359,7 @@ static void __cpuinfo_store_cpu(struct cpuinfo_arm64 *info)
 	info->reg_dczid = read_cpuid(DCZID_EL0);
 	info->reg_midr = read_cpuid_id();
 	info->reg_revidr = read_cpuid(REVIDR_EL1);
+	info->reg_gmid = read_cpuid(GMID_EL1);
 
 	info->reg_id_aa64dfr0 = read_cpuid(ID_AA64DFR0_EL1);
 	info->reg_id_aa64dfr1 = read_cpuid(ID_AA64DFR1_EL1);