linux-kernel - [PATCH v3 3/7] arm64: kpti: move check for non-vulnerable CPUs to a function

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Message-Id: <20190109235544.2992426-4-jeremy.linton@arm.com>
Date:   Wed,  9 Jan 2019 17:55:40 -0600
From:   Jeremy Linton <jeremy.linton@....com>
To:     linux-arm-kernel@...ts.infradead.org
Cc:     catalin.marinas@....com, will.deacon@....com, marc.zyngier@....com,
        suzuki.poulose@....com, dave.martin@....com,
        shankerd@...eaurora.org, linux-kernel@...r.kernel.org,
        ykaukab@...e.de, julien.thierry@....com, mlangsdo@...hat.com,
        steven.price@....com, stefan.wahren@...e.com,
        Jeremy Linton <jeremy.linton@....com>
Subject: [PATCH v3 3/7] arm64: kpti: move check for non-vulnerable CPUs to a function

From: Mian Yousaf Kaukab <ykaukab@...e.de>

Add is_meltdown_safe() which is a whitelist of known safe cores.

Signed-off-by: Mian Yousaf Kaukab <ykaukab@...e.de>
[Moved location of function]
Signed-off-by: Jeremy Linton <jeremy.linton@....com>
---
 arch/arm64/kernel/cpufeature.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 4f272399de89..ab784d7a0083 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -947,8 +947,7 @@ has_useable_cnp(const struct arm64_cpu_capabilities *entry, int scope)
 #ifdef CONFIG_UNMAP_KERNEL_AT_EL0
 static int __kpti_forced; /* 0: not forced, >0: forced on, <0: forced off */
 
-static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
-				int scope)
+static bool is_cpu_meltdown_safe(void)
 {
 	/* List of CPUs that are not vulnerable and don't need KPTI */
 	static const struct midr_range kpti_safe_list[] = {
@@ -962,6 +961,15 @@ static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
 		MIDR_ALL_VERSIONS(MIDR_CORTEX_A73),
 		{ /* sentinel */ }
 	};
+	if (is_midr_in_range_list(read_cpuid_id(), kpti_safe_list))
+		return true;
+
+	return false;
+}
+
+static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
+				int scope)
+{
 	char const *str = "command line option";
 
 	/*
@@ -985,8 +993,7 @@ static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
 	if (IS_ENABLED(CONFIG_RANDOMIZE_BASE))
 		return true;
 
-	/* Don't force KPTI for CPUs that are not vulnerable */
-	if (is_midr_in_range_list(read_cpuid_id(), kpti_safe_list))
+	if (is_cpu_meltdown_safe())
 		return false;
 
 	/* Defer to CPU feature registers */
-- 
2.17.2