linux-kernel - [PATCH 3/3] arm64: cpufeature: Trap CTR_EL0 access only where it is necessary

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Message-Id: <20181004083315.31174-4-suzuki.poulose@arm.com>
Date:   Thu,  4 Oct 2018 09:33:15 +0100
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     linux-arm-kernel@...ts.infradead.org
Cc:     linux-kernel@...r.kernel.org, catalin.marinas@....com,
        will.deacon@....com, mark.rutland@....com, suzuki.poulose@....com,
        pelcan@...eaurora.org, shankerd@...eaurora.org
Subject: [PATCH 3/3] 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@....com>
Cc: Will Deacon <will.deacon@....com>
Cc: Catalin Marinas <catalin.marinas@....com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
---
 arch/arm64/kernel/cpu_errata.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
index 31551f444ce3..e07ba717860e 100644
--- a/arch/arm64/kernel/cpu_errata.c
+++ b/arch/arm64/kernel/cpu_errata.c
@@ -84,7 +84,12 @@ 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);
-- 
2.19.0