powerpc/8xx: Refactor kernel address boundary comparison

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@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/6312575d06a8813105e6564a3b12e1d373aa1b2f.1589866984.git.christophe.leroy@csgroup.eu

diff --git a/arch/powerpc/kernel/head_8xx.S b/arch/powerpc/kernel/head_8xx.S
index 9f3f7f3d03a764748a7de111e8771c4f462974db..9a117b9f09988f296f4f98891e2beb87d1fa2619 100644 (file)
--- a/arch/powerpc/kernel/head_8xx.S
+++ b/arch/powerpc/kernel/head_8xx.S
@@ -32,10 +32,15 @@
 
 #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:
@@ -209,20 +214,11 @@ 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:
@@ -288,9 +284,7 @@ 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