arm64: Delay initialisation of cpuinfo_arm64::reg_{zcr,smcr}

Even if we are now able to tell the kernel to avoid exposing SVE/SME
from the command line, we still have a couple of places where we
unconditionally access the ZCR_EL1 (resp. SMCR_EL1) registers.

On systems with broken firmwares, this results in a crash even if
arm64.nosve (resp. arm64.nosme) was passed on the command-line.

To avoid this, only update cpuinfo_arm64::reg_{zcr,smcr} once
we have computed the sanitised version for the corresponding
feature registers (ID_AA64PFR0 for SVE, and ID_AA64PFR1 for
SME). This results in some minor refactoring.
Reviewed-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Peter Collingbourne <pcc@google.com>
Tested-by: Peter Collingbourne <pcc@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220720105219.1755096-1-maz@kernel.orgSigned-off-by: Will Deacon <will@kernel.org>

arch/arm64/kernel/cpufeature.c

@@ -1001,15 +1001,24 @@ void __init init_cpu_features(struct cpuinfo_arm64 *info)
 	if (id_aa64pfr0_32bit_el0(info->reg_id_aa64pfr0))
 		init_32bit_cpu_features(&info->aarch32);
 
-	if (id_aa64pfr0_sve(info->reg_id_aa64pfr0)) {
+	if (IS_ENABLED(CONFIG_ARM64_SVE) &&
+	    id_aa64pfr0_sve(read_sanitised_ftr_reg(SYS_ID_AA64PFR0_EL1))) {
+		info->reg_zcr = read_zcr_features();
 		init_cpu_ftr_reg(SYS_ZCR_EL1, info->reg_zcr);
 		vec_init_vq_map(ARM64_VEC_SVE);
 	}
 
-	if (id_aa64pfr1_sme(info->reg_id_aa64pfr1)) {
+	if (IS_ENABLED(CONFIG_ARM64_SME) &&
+	    id_aa64pfr1_sme(read_sanitised_ftr_reg(SYS_ID_AA64PFR1_EL1))) {
+		info->reg_smcr = read_smcr_features();
+		/*
+		 * We mask out SMPS since even if the hardware
+		 * supports priorities the kernel does not at present
+		 * and we block access to them.
+		 */
+		info->reg_smidr = read_cpuid(SMIDR_EL1) & ~SMIDR_EL1_SMPS;
 		init_cpu_ftr_reg(SYS_SMCR_EL1, info->reg_smcr);
-		if (IS_ENABLED(CONFIG_ARM64_SME))
-			vec_init_vq_map(ARM64_VEC_SME);
+		vec_init_vq_map(ARM64_VEC_SME);
 	}
 
 	if (id_aa64pfr1_mte(info->reg_id_aa64pfr1))
@@ -1241,23 +1250,31 @@ void update_cpu_features(int cpu,
 	taint |= check_update_ftr_reg(SYS_ID_AA64SMFR0_EL1, cpu,
 				      info->reg_id_aa64smfr0, boot->reg_id_aa64smfr0);
 
-	if (id_aa64pfr0_sve(info->reg_id_aa64pfr0)) {
+	if (IS_ENABLED(CONFIG_ARM64_SVE) &&
+	    id_aa64pfr0_sve(read_sanitised_ftr_reg(SYS_ID_AA64PFR0_EL1))) {
+		info->reg_zcr = read_zcr_features();
 		taint |= check_update_ftr_reg(SYS_ZCR_EL1, cpu,
 					info->reg_zcr, boot->reg_zcr);
 
-		/* Probe vector lengths, unless we already gave up on SVE */
-		if (id_aa64pfr0_sve(read_sanitised_ftr_reg(SYS_ID_AA64PFR0_EL1)) &&
-		    !system_capabilities_finalized())
+		/* Probe vector lengths */
+		if (!system_capabilities_finalized())
 			vec_update_vq_map(ARM64_VEC_SVE);
 	}
 
-	if (id_aa64pfr1_sme(info->reg_id_aa64pfr1)) {
+	if (IS_ENABLED(CONFIG_ARM64_SME) &&
+	    id_aa64pfr1_sme(read_sanitised_ftr_reg(SYS_ID_AA64PFR1_EL1))) {
+		info->reg_smcr = read_smcr_features();
+		/*
+		 * We mask out SMPS since even if the hardware
+		 * supports priorities the kernel does not at present
+		 * and we block access to them.
+		 */
+		info->reg_smidr = read_cpuid(SMIDR_EL1) & ~SMIDR_EL1_SMPS;
 		taint |= check_update_ftr_reg(SYS_SMCR_EL1, cpu,
 					info->reg_smcr, boot->reg_smcr);
 
-		/* Probe vector lengths, unless we already gave up on SME */
-		if (id_aa64pfr1_sme(read_sanitised_ftr_reg(SYS_ID_AA64PFR1_EL1)) &&
-		    !system_capabilities_finalized())
+		/* Probe vector lengths */
+		if (!system_capabilities_finalized())
 			vec_update_vq_map(ARM64_VEC_SME);
 	}
 

arch/arm64/kernel/cpuinfo.c

@@ -439,22 +439,6 @@ static void __cpuinfo_store_cpu(struct cpuinfo_arm64 *info)
 	if (id_aa64pfr0_32bit_el0(info->reg_id_aa64pfr0))
 		__cpuinfo_store_cpu_32bit(&info->aarch32);
 
-	if (IS_ENABLED(CONFIG_ARM64_SVE) &&
-	    id_aa64pfr0_sve(info->reg_id_aa64pfr0))
-		info->reg_zcr = read_zcr_features();
-
-	if (IS_ENABLED(CONFIG_ARM64_SME) &&
-	    id_aa64pfr1_sme(info->reg_id_aa64pfr1)) {
-		info->reg_smcr = read_smcr_features();
-
-		/*
-		 * We mask out SMPS since even if the hardware
-		 * supports priorities the kernel does not at present
-		 * and we block access to them.
-		 */
-		info->reg_smidr = read_cpuid(SMIDR_EL1) & ~SMIDR_EL1_SMPS;
-	}
-
 	cpuinfo_detect_icache_policy(info);
 }