4.9-stable review patch. If anyone has any objections, please let me know.
------------------
From: Marc Zyngier <marc.zyngier@xxxxxxx>
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.zyngier@xxxxxxx>
[will: Update comment]
Signed-off-by: Will Deacon <will.deacon@xxxxxxx>
Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx>
[Alex: use cpus_have_cap as cpus_have_const_cap doesn't exist in v4.9]
Signed-off-by: Alex Shi <alex.shi@xxxxxxxxxx> [v4.9 backport]
Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx> [v4.9 backport]
Tested-by: Will Deacon <will.deacon@xxxxxxx>
Tested-by: Greg Hackmann <ghackmann@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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;
}