arm64: cpufeature: Trap CTR_EL0 access only where it is necessary

When there is a mismatch in the CTR_EL0 field, we trap
access to CTR from EL0 on all CPUs to expose the safe
value. However, we could skip trapping on a CPU which
matches the safe value.

Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/kernel/cpu_errata.c

@@ -99,7 +99,12 @@ has_mismatched_cache_type(const struct arm64_cpu_capabilities *entry,
 static void
 cpu_enable_trap_ctr_access(const struct arm64_cpu_capabilities *__unused)
 {
-	sysreg_clear_set(sctlr_el1, SCTLR_EL1_UCT, 0);
+	u64 mask = arm64_ftr_reg_ctrel0.strict_mask;
+
+	/* Trap CTR_EL0 access on this CPU, only if it has a mismatch */
+	if ((read_cpuid_cachetype() & mask) !=
+	    (arm64_ftr_reg_ctrel0.sys_val & mask))
+		sysreg_clear_set(sctlr_el1, SCTLR_EL1_UCT, 0);
 }
 
 atomic_t arm64_el2_vector_last_slot = ATOMIC_INIT(-1);