[PATCH 3/6] ARM: spectre-bhb: simplify BPIALL vector macro

[Ard Biesheuvel]

The BPIALL mitigation for Spectre-BHB adds a single instruction to the
handler sequence that doesn't clobber any registers. Given that these
sequences are 10 instructions long, they don't fit neatly into a
cacheline anyway, so we can simply move that single instruction to the
start of it, and rearrange the symbol names accordingly.

Signed-off-by: Ard Biesheuvel <ardb at kernel.org>
---
 arch/arm/kernel/entry-armv.S | 21 ++++++--------------
 1 file changed, 6 insertions(+), 15 deletions(-)

diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
index 4bbd92d41031..a5725e82addc 100644
--- a/arch/arm/kernel/entry-armv.S
+++ b/arch/arm/kernel/entry-armv.S
@@ -996,6 +996,12 @@ __kuser_helper_end:
  */
 	.macro	vector_stub, name, mode, correction=0
 	.align	5
+#ifdef CONFIG_HARDEN_BRANCH_HISTORY
+vector_bhb_bpiall_\name:
+	mcr	p15, 0, r0, c7, c5, 6	@ BPIALL
+	@ isb not needed due to "movs pc, lr" in the vector stub
+	@ which gives a "context synchronisation".
+#endif
 
 vector_\name:
 	.if \correction
@@ -1047,21 +1053,6 @@ vector_bhb_loop8_\name:
 	isb
 	b	2b
 ENDPROC(vector_bhb_loop8_\name)
-
-vector_bhb_bpiall_\name:
-	.if \correction
-	sub	lr, lr, #\correction
-	.endif
-
-	@ Save r0, lr_<exception> (parent PC)
-	stmia	sp, {r0, lr}
-
-	@ bhb workaround
-	mcr	p15, 0, r0, c7, c5, 6	@ BPIALL
-	@ isb not needed due to "movs pc, lr" in the vector stub
-	@ which gives a "context synchronisation".
-	b	2b
-ENDPROC(vector_bhb_bpiall_\name)
 	.previous
 #endif
 
-- 
2.30.2