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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: 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>
hifive-unleashed-5.1
Marc Zyngier 2018-01-29 11:59:56 +00:00 committed by Catalin Marinas
parent f992b4dfd5
commit 6dc52b15c4
1 changed files with 14 additions and 3 deletions
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17
arch/arm64/kernel/cpufeature.c
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@ -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;
}