[PATCH] arm64: Restore forced disabling of KPTI on ThunderX

[dann frazier]

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 at arm.com>
Cc: stable at vger.kernel.org # 5.13+
Signed-off-by: dann frazier <dann.frazier at canonical.com>
---
 arch/arm64/kernel/cpufeature.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index f8a3067d10c6..7275b49034f3 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -1528,7 +1528,7 @@ static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
 	 * 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)) {
+	if (this_cpu_has_cap(ARM64_WORKAROUND_CAVIUM_27456)) {
 		str = "ARM64_WORKAROUND_CAVIUM_27456";
 		__kpti_forced = -1;
 	}
-- 
2.33.0