[PATCH 4.14 10/27] arm64: entry: Make the trampoline cleanup optional

From: Greg Kroah-Hartman
Date: Fri Apr 01 2022 - 02:39:17 EST

From: James Morse <james.morse@xxxxxxx>

commit d739da1694a0eaef0358a42b76904b611539b77b upstream.

Subsequent patches will add additional sets of vectors that use
the same tricks as the kpti vectors to reach the full-fat vectors.
The full-fat vectors contain some cleanup for kpti that is patched
in by alternatives when kpti is in use. Once there are additional
vectors, the cleanup will be needed in more cases.

But on big/little systems, the cleanup would be harmful if no
trampoline vector were in use. Instead of forcing CPUs that don't
need a trampoline vector to use one, make the trampoline cleanup

Entry at the top of the vectors will skip the cleanup. The trampoline
vectors can then skip the first instruction, triggering the cleanup
to run.

Reviewed-by: Russell King (Oracle) <rmk+kernel@xxxxxxxxxxxxxxx>
Reviewed-by: Catalin Marinas <catalin.marinas@xxxxxxx>
Signed-off-by: James Morse <james.morse@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
arch/arm64/kernel/entry.S | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)

--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -76,16 +76,20 @@
.align 7
-alternative_if ARM64_UNMAP_KERNEL_AT_EL0
.if \el == 0
+ /*
+ * This must be the first instruction of the EL0 vector entries. It is
+ * skipped by the trampoline vectors, to trigger the cleanup.
+ */
+ b .Lskip_tramp_vectors_cleanup\@
.if \regsize == 64
mrs x30, tpidrro_el0
msr tpidrro_el0, xzr
mov x30, xzr

sub sp, sp, #S_FRAME_SIZE
@@ -1035,7 +1039,7 @@ alternative_insn isb, nop, ARM64_WORKARO
prfm plil1strm, [x30, #(1b - tramp_vectors)]
msr vbar_el1, x30
- add x30, x30, #(1b - tramp_vectors)
+ add x30, x30, #(1b - tramp_vectors + 4)
.org 1b + 128 // Did we overflow the ventry slot?