Commit 8703f27d authored by Will Deacon's avatar Will Deacon Committed by Greg Kroah-Hartman
Browse files

arm64: entry: Reword comment about post_ttbr_update_workaround


Commit f167211a

 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: default avatarWill Deacon <will.deacon@arm.com>
Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
Signed-off-by: default avatarArd Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent e39247ca
......@@ -962,16 +962,9 @@ alternative_else_nop_endif
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
......
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