This is a note to let you know that I've just added the patch titled
arm64: Restore forced disabling of KPTI on ThunderX
to the 5.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
arm64-restore-forced-disabling-of-kpti-on-thunderx.patch
and it can be found in the queue-5.14 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 22b70e6f2da0a4c8b1421b00cfc3016bc9d4d9d4 Mon Sep 17 00:00:00 2001
From: dann frazier <dann.frazier@xxxxxxxxxxxxx>
Date: Thu, 23 Sep 2021 08:50:02 -0600
Subject: arm64: Restore forced disabling of KPTI on ThunderX
From: dann frazier <dann.frazier@xxxxxxxxxxxxx>
commit 22b70e6f2da0a4c8b1421b00cfc3016bc9d4d9d4 upstream.
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@xxxxxxxxxxxxxxx> # 5.13.x
Signed-off-by: dann frazier <dann.frazier@xxxxxxxxxxxxx>
Suggested-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
Reviewed-by: Mark Brown <broonie@xxxxxxxxxx>
Acked-by: Marc Zyngier <maz@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20210923145002.3394558-1-dann.frazier@xxxxxxxxxxxxx
Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/arm64/kernel/cpufeature.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -1500,9 +1500,13 @@ static bool unmap_kernel_at_el0(const st
/*
* 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;
}
Patches currently in stable-queue which might be from dann.frazier@xxxxxxxxxxxxx are
queue-5.14/arm64-restore-forced-disabling-of-kpti-on-thunderx.patch
