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Commit 6dc52b15 authored by Marc Zyngier's avatar Marc Zyngier Committed by Catalin Marinas
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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: default avatarMarc Zyngier <marc.zyngier@arm.com>
[will: Update comment]
Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>

Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
parent f992b4df

arch/arm64/kernel/cpufeature.c

+14 −3
Original line number Diff line number Diff line
@@ -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;

	}