path: root/arch
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authordann frazier <dann.frazier@canonical.com>2021-09-23 08:50:02 -0600
committerCatalin Marinas <catalin.marinas@arm.com>2021-09-23 15:59:15 +0100
commit22b70e6f2da0a4c8b1421b00cfc3016bc9d4d9d4 (patch)
treebbd4e04dcf32a7db7296e56a6d1905389d2c9288 /arch
parent0e3dbf765fe22060acbcb8eb8c4d256e655a1247 (diff)
arm64: Restore forced disabling of KPTI on ThunderX
A noted side-effect of commit 0c6c2d3615ef ("arm64: Generate cpucaps.h") is that cpucaps are now sorted, changing the enumeration order. This assumed no dependencies between cpucaps, which turned out not to be true in one case. UNMAP_KERNEL_AT_EL0 currently needs to be processed after WORKAROUND_CAVIUM_27456. ThunderX systems are incompatible with KPTI, so unmap_kernel_at_el0() bails if WORKAROUND_CAVIUM_27456 is set. But because of the sorting, WORKAROUND_CAVIUM_27456 will not yet have been considered when unmap_kernel_at_el0() checks for it, so the kernel tries to run w/ KPTI - and quickly falls over. Because all ThunderX implementations have homogeneous CPUs, we can remove this dependency by just checking the current CPU for the erratum. Fixes: 0c6c2d3615ef ("arm64: Generate cpucaps.h") Cc: <stable@vger.kernel.org> # 5.13.x Signed-off-by: dann frazier <dann.frazier@canonical.com> Suggested-by: Suzuki K Poulose <suzuki.poulose@arm.com> Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com> Reviewed-by: Mark Brown <broonie@kernel.org> Acked-by: Marc Zyngier <maz@kernel.org> Link: https://lore.kernel.org/r/20210923145002.3394558-1-dann.frazier@canonical.com Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Diffstat (limited to 'arch')
1 files changed, 6 insertions, 2 deletions
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index f8a3067d10c6..6ec7036ef7e1 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -1526,9 +1526,13 @@ static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
* 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.
+ * ends as well as you might imagine. Don't even try. We cannot rely
+ * on the cpus_have_*cap() helpers here to detect the CPU erratum
+ * because cpucap detection order may change. However, since we know
+ * affected CPUs are always in a homogeneous configuration, it is
+ * safe to rely on this_cpu_has_cap() here.
- if (cpus_have_const_cap(ARM64_WORKAROUND_CAVIUM_27456)) {
+ if (this_cpu_has_cap(ARM64_WORKAROUND_CAVIUM_27456)) {
str = "ARM64_WORKAROUND_CAVIUM_27456";
__kpti_forced = -1;