linux-kernel - [PATCH 4.14 014/185] arm64: kpti: Whitelist Cortex-A CPUs that dont implement the CSV3 field

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Date:   Thu,  3 Oct 2019 17:51:32 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Will Deacon <will.deacon@....com>,
        Niklas Cassel <niklas.cassel@...aro.org>
Subject: [PATCH 4.14 014/185] arm64: kpti: Whitelist Cortex-A CPUs that dont implement the CSV3 field

From: Will Deacon <will.deacon@....com>

commit 2a355ec25729053bb9a1a89b6c1d1cdd6c3b3fb1 upstream.

While the CSV3 field of the ID_AA64_PFR0 CPU ID register can be checked
to see if a CPU is susceptible to Meltdown and therefore requires kpti
to be enabled, existing CPUs do not implement this field.

We therefore whitelist all unaffected Cortex-A CPUs that do not implement
the CSV3 field.

Signed-off-by: Will Deacon <will.deacon@....com>
Signed-off-by: Niklas Cassel <niklas.cassel@...aro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/arm64/kernel/cpufeature.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -838,6 +838,11 @@ static bool unmap_kernel_at_el0(const st
 	switch (read_cpuid_id() & MIDR_CPU_MODEL_MASK) {
 	case MIDR_CAVIUM_THUNDERX2:
 	case MIDR_BRCM_VULCAN:
+	case MIDR_CORTEX_A53:
+	case MIDR_CORTEX_A55:
+	case MIDR_CORTEX_A57:
+	case MIDR_CORTEX_A72:
+	case MIDR_CORTEX_A73:
 		return false;
 	}