From: Marc Zyngier <marc.zyngier@arm.com>
Date: Mon, 29 Jan 2018 11:59:56 +0000 (+0000)
Subject: arm64: Force KPTI to be disabled on Cavium ThunderX
X-Git-Tag: v5.15~9433^2~32
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=6dc52b15c4a48052ade2529d639eee401d76e469;p=platform%2Fkernel%2Flinux-starfive.git

arm64: Force KPTI to be disabled on Cavium ThunderX

Cavium ThunderX's erratum 27456 results in a corruption of icache
entries that are loaded from memory that is mapped as non-global
(i.e. ASID-tagged).

As KPTI is based on memory being mapped non-global, let's prevent
it from kicking in if this erratum is detected.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
[will: Update comment]
Signed-off-by: Will Deacon <will.deacon@arm.com>

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
---

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index cd9f469..0ff8ab7 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -855,12 +855,23 @@ 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 __unused)
 {
+	char const *str = "command line option";
 	u64 pfr0 = read_sanitised_ftr_reg(SYS_ID_AA64PFR0_EL1);
 
-	/* Forced on command line? */
+	/*
+	 * For reasons that aren't entirely clear, enabling KPTI on Cavium
+	 * ThunderX leads to apparent I-cache corruption of kernel text, which
+	 * ends as well as you might imagine. Don't even try.
+	 */
+	if (cpus_have_const_cap(ARM64_WORKAROUND_CAVIUM_27456)) {
+		str = "ARM64_WORKAROUND_CAVIUM_27456";
+		__kpti_forced = -1;
+	}
+
+	/* Forced? */
 	if (__kpti_forced) {
-		pr_info_once("kernel page table isolation forced %s by command line option\n",
-			     __kpti_forced > 0 ? "ON" : "OFF");
+		pr_info_once("kernel page table isolation forced %s by %s\n",
+			     __kpti_forced > 0 ? "ON" : "OFF", str);
 		return __kpti_forced > 0;
 	}