| Message ID | 20210923145002.3394558-1-dann.frazier@canonical.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2] arm64: Restore forced disabling of KPTI on ThunderX | expand |
On Thu, 23 Sep 2021 08:50:02 -0600, dann frazier wrote: > 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. > > [...] Applied to arm64 (for-next/fixes), thanks! [1/1] arm64: Restore forced disabling of KPTI on ThunderX https://git.kernel.org/arm64/c/22b70e6f2da0
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; }
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") Suggested-by: Suzuki K Poulose <suzuki.poulose@arm.com> Cc: stable@vger.kernel.org # 5.13+ Signed-off-by: dann frazier <dann.frazier@canonical.com> Reviewed-by: Mark Brown <broonie@kernel.org> Acked-by: Marc Zyngier <maz@kernel.org> [ dannf: Added comment text ] Signed-off-by: dann frazier <dann.frazier@canonical.com> Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com> --- arch/arm64/kernel/cpufeature.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)