arm64: cpufeature: Fix handling of CTR_EL0.IDC field

CTR_EL0.IDC reports the data cache clean requirements for instruction
to data coherence. However, if the field is 0, we need to check the
CLIDR_EL1 fields to detect the status of the feature. Currently we
don't do this and generate a warning with tainting the kernel, when
there is a mismatch in the field among the CPUs. Also the userspace
doesn't have a reliable way to check the CLIDR_EL1 register to check
the status.

This patch fixes the problem by checking the CLIDR_EL1 fields, when
(CTR_EL0.IDC == 0) and updates the kernel's copy of the CTR_EL0 for
the CPU with the actual status of the feature. This would allow the
sanity check infrastructure to do the proper checking of the fields
and also allow the CTR_EL0 emulation code to supply the real status
of the feature.

Now, if a CPU has raw CTR_EL0.IDC == 0 and effective IDC == 1 (with
overall system wide IDC == 1), we need to expose the real value to
the user. So, we trap CTR_EL0 access on the CPU which reports incorrect
CTR_EL0.IDC.

Fixes: commit 6ae4b6e057888 ("arm64: Add support for new control bits CTR_EL0.DIC and CTR_EL0.IDC")
Cc: Shanker Donthineni <shankerd@codeaurora.org>
Cc: Philip Elcan <pelcan@codeaurora.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

1 files changed, 24 insertions, 3 deletions

diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
index cde948991d68..3deb01c6ed49 100644
--- a/arch/arm64/kernel/cpu_errata.c
+++ b/arch/arm64/kernel/cpu_errata.c
@@ -68,11 +68,32 @@ static bool
 has_mismatched_cache_type(const struct arm64_cpu_capabilities *entry,
 			  int scope)
 {
-	u64 mask = arm64_ftr_reg_ctrel0.strict_mask;;
+	u64 mask = arm64_ftr_reg_ctrel0.strict_mask;
+	u64 sys = arm64_ftr_reg_ctrel0.sys_val & mask;
+	u64 ctr_raw, ctr_real;
 
 	WARN_ON(scope != SCOPE_LOCAL_CPU || preemptible());
-	return (read_cpuid_cachetype() & mask) !=
-	       (arm64_ftr_reg_ctrel0.sys_val & mask);
+
+	/*
+	 * We want to make sure that all the CPUs in the system expose
+	 * a consistent CTR_EL0 to make sure that applications behaves
+	 * correctly with migration.
+	 *
+	 * If a CPU has CTR_EL0.IDC but does not advertise it via CTR_EL0 :
+	 *
+	 * 1) It is safe if the system doesn't support IDC, as CPU anyway
+	 *    reports IDC = 0, consistent with the rest.
+	 *
+	 * 2) If the system has IDC, it is still safe as we trap CTR_EL0
+	 *    access on this CPU via the ARM64_HAS_CACHE_IDC capability.
+	 *
+	 * So, we need to make sure either the raw CTR_EL0 or the effective
+	 * CTR_EL0 matches the system's copy to allow a secondary CPU to boot.
+	 */
+	ctr_raw = read_cpuid_cachetype() & mask;
+	ctr_real = read_cpuid_effective_cachetype() & mask;
+
+	return (ctr_real != sys) && (ctr_raw != sys);
 }
 
 static void