From: Mark Rutland <mark.rutland@arm.com>
Date: Wed, 6 Jan 2016 11:05:27 +0000 (+0000)
Subject: UPSTREAM: arm64: head.S: use memset to clear BSS
X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=a725004a74ab543510a8158b206c334756e9d8cf;p=GitHub%2Fexynos8895%2Fandroid_kernel_samsung_universal8895.git

UPSTREAM: arm64: head.S: use memset to clear BSS

Currently we use an open-coded memzero to clear the BSS. As it is a
trivial implementation, it is sub-optimal.

Our optimised memset doesn't use the stack, is position-independent, and
for the memzero case can use of DC ZVA to clear large blocks
efficiently. In __mmap_switched the MMU is on and there are no live
caller-saved registers, so we can safely call an uninstrumented memset.

This patch changes __mmap_switched to use memset when clearing the BSS.
We use the __pi_memset alias so as to avoid any instrumentation in all
kernel configurations.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

Bug: 30369029
Patchset: rework-pagetable

(cherry picked from commit 2a803c4db615d85126c5c7afd5849a3cfde71422)
Signed-off-by: Jeff Vander Stoep <jeffv@google.com>
Change-Id: I3dc7050fe5566f2126cbea9abfa6063c8e6b029a
---

diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index 17ce7285bb12..917d98108b3f 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -415,14 +415,13 @@ ENDPROC(__create_page_tables)
  */
 	.set	initial_sp, init_thread_union + THREAD_START_SP
 __mmap_switched:
-	adr_l	x6, __bss_start
-	adr_l	x7, __bss_stop
-
-1:	cmp	x6, x7
-	b.hs	2f
-	str	xzr, [x6], #8			// Clear BSS
-	b	1b
-2:
+	// Clear BSS
+	adr_l	x0, __bss_start
+	mov	x1, xzr
+	adr_l	x2, __bss_stop
+	sub	x2, x2, x0
+	bl	__pi_memset
+
 	adr_l	sp, initial_sp, x4
 	mov	x4, sp
 	and	x4, x4, #~(THREAD_SIZE - 1)