From mboxrd@z Thu Jan 1 00:00:00 1970 From: will.deacon@arm.com (Will Deacon) Date: Fri, 26 Jan 2018 12:03:15 +0000 Subject: [PATCH 5/7] arm64: Force KPTI to be disabled on Cavium ThunderX In-Reply-To: <1516968197-23206-1-git-send-email-will.deacon@arm.com> References: <1516968197-23206-1-git-send-email-will.deacon@arm.com> Message-ID: <1516968197-23206-6-git-send-email-will.deacon@arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org From: Marc Zyngier 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 [will: Update comment] Signed-off-by: Will Deacon --- arch/arm64/kernel/cpufeature.c | 17 ++++++++++++++--- 1 file changed, 14 insertions(+), 3 deletions(-) diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c index cd9f46952db3..0ff8ab79352c 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; } -- 2.1.4