summaryrefslogtreecommitdiff
path: root/arch/arm64/kernel
diff options
context:
space:
mode:
authorWill Deacon <will.deacon@arm.com>2018-04-03 12:09:22 +0100
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2018-04-08 12:12:56 +0200
commita80d8e2979f32113df09b844d5e12e771162db40 (patch)
tree31f3ea2192ba2223400629b85e5d82d3487e49da /arch/arm64/kernel
parentda93510bae26c62cc6171d8cdbe177a091a1ab79 (diff)
arm64: entry: Reword comment about post_ttbr_update_workaround
commit f167211a93ac upstream. We don't fully understand the Cavium ThunderX erratum, but it appears that mapping the kernel as nG can lead to horrible consequences such as attempting to execute userspace from kernel context. Since kpti isn't enabled for these CPUs anyway, simplify the comment justifying the lack of post_ttbr_update_workaround in the exception trampoline. Signed-off-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com> Signed-off-by: Alex Shi <alex.shi@linaro.org> [v4.9 backport] Signed-off-by: Mark Rutland <mark.rutland@arm.com> [v4.9 backport] Tested-by: Will Deacon <will.deacon@arm.com> Tested-by: Greg Hackmann <ghackmann@google.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'arch/arm64/kernel')
-rw-r--r--arch/arm64/kernel/entry.S13
1 files changed, 3 insertions, 10 deletions
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index f35ca1e54b5a..8d1600b18562 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -861,16 +861,9 @@ __ni_sys_trace:
orr \tmp, \tmp, #USER_ASID_FLAG
msr ttbr1_el1, \tmp
/*
- * We avoid running the post_ttbr_update_workaround here because the
- * user and kernel ASIDs don't have conflicting mappings, so any
- * "blessing" as described in:
- *
- * http://lkml.kernel.org/r/56BB848A.6060603@caviumnetworks.com
- *
- * will not hurt correctness. Whilst this may partially defeat the
- * point of using split ASIDs in the first place, it avoids
- * the hit of invalidating the entire I-cache on every return to
- * userspace.
+ * We avoid running the post_ttbr_update_workaround here because
+ * it's only needed by Cavium ThunderX, which requires KPTI to be
+ * disabled.
*/
.endm