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From:   Christophe Leroy <christophe.leroy@c-s.fr>
Subject: [PATCH v1 38/46] powerpc/8xx: Refactor kernel address boundary
 comparison
To:     Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>
Cc:     linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
Date:   Mon, 16 Mar 2020 12:36:24 +0000 (UTC)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Now that linear and IMMR dedicated TLB handling is gone, kernel
boundary address comparison is similar in ITLB miss handler and
in DTLB miss handler.

Create a macro named compare_to_kernel_boundary.

When TASK_SIZE is strictly below 0x80000000 and PAGE_OFFSET is
above 0x80000000, it is enough to compare to 0x8000000, and this
can be done with a single instruction.

Using not. instruction, we get to use 'blt' conditional branch as
when doing a regular comparison:

0x00000000 <= addr <= 0x7fffffff ==>
0xffffffff >= NOT(addr) >= 0x80000000
The above test corresponds to a 'blt'

Otherwise, do a regular comparison using two instructions.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
---
 arch/powerpc/kernel/head_8xx.S | 22 ++++++++--------------
 1 file changed, 8 insertions(+), 14 deletions(-)

diff --git a/arch/powerpc/kernel/head_8xx.S b/arch/powerpc/kernel/head_8xx.S
index d12f5846d527..410cb48ab36f 100644
--- a/arch/powerpc/kernel/head_8xx.S
+++ b/arch/powerpc/kernel/head_8xx.S
@@ -31,10 +31,15 @@
 
 #include "head_32.h"
 
+.macro compare_to_kernel_boundary scratch, addr
 #if CONFIG_TASK_SIZE <= 0x80000000 && CONFIG_PAGE_OFFSET >= 0x80000000
 /* By simply checking Address >= 0x80000000, we know if its a kernel address */
-#define SIMPLE_KERNEL_ADDRESS		1
+	not.	\scratch, \addr
+#else
+	rlwinm	\scratch, \addr, 16, 0xfff8
+	cmpli	cr0, \scratch, PAGE_OFFSET@h
 #endif
+.endm
 
 /*
  * We need an ITLB miss handler for kernel addresses if:
@@ -208,20 +213,11 @@ InstructionTLBMiss:
 	mtspr	SPRN_MD_EPN, r10
 #ifdef ITLB_MISS_KERNEL
 	mfcr	r11
-#if defined(SIMPLE_KERNEL_ADDRESS)
-	cmpi	cr0, r10, 0	/* Address >= 0x80000000 */
-#else
-	rlwinm	r10, r10, 16, 0xfff8
-	cmpli	cr0, r10, PAGE_OFFSET@h
-#endif
+	compare_to_kernel_boundary r10, r10
 #endif
 	mfspr	r10, SPRN_M_TWB	/* Get level 1 table */
 #ifdef ITLB_MISS_KERNEL
-#if defined(SIMPLE_KERNEL_ADDRESS)
-	bge+	3f
-#else
 	blt+	3f
-#endif
 	rlwinm	r10, r10, 0, 20, 31
 	oris	r10, r10, (swapper_pg_dir - PAGE_OFFSET)@ha
 3:
@@ -287,9 +283,7 @@ DataStoreTLBMiss:
 	 * kernel page tables.
 	 */
 	mfspr	r10, SPRN_MD_EPN
-	rlwinm	r10, r10, 16, 0xfff8
-	cmpli	cr0, r10, PAGE_OFFSET@h
-
+	compare_to_kernel_boundary r10, r10
 	mfspr	r10, SPRN_M_TWB	/* Get level 1 table */
 	blt+	3f
 	rlwinm	r10, r10, 0, 20, 31
-- 
2.25.0