4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Marc Zyngier <marc.zyng...@arm.com>

commit 6dc52b15c4a4 upstream.

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.zyng...@arm.com>
[will: Update comment]
Signed-off-by: Will Deacon <will.dea...@arm.com>
Signed-off-by: Catalin Marinas <catalin.mari...@arm.com>
[Alex: use cpus_have_cap as cpus_have_const_cap doesn't exist in v4.9]
Signed-off-by: Alex Shi <alex....@linaro.org> [v4.9 backport]
Signed-off-by: Mark Rutland <mark.rutl...@arm.com> [v4.9 backport]
Tested-by: Will Deacon <will.dea...@arm.com>
Tested-by: Greg Hackmann <ghackm...@google.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
 arch/arm64/kernel/cpufeature.c |   17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -753,12 +753,23 @@ static int __kpti_forced; /* 0: not forc
 static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
                                int __unused)
 {
+       char const *str = "command line option";
        u64 pfr0 = read_system_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_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;
        }
 


Reply via email to