[PATCH] powerpc/8xx: Simplify pte_update() with 16k pages

[PATCH] powerpc/8xx: Simplify pte_update() with 16k pages

[Christophe Leroy]

While looking at code generated for code patching, I saw that
pte_clear generated:

 2d8:	38 a0 00 00 	li      r5,0
 2dc:	38 e0 10 00 	li      r7,4096
 2e0:	39 00 20 00 	li      r8,8192
 2e4:	39 40 30 00 	li      r10,12288
 2e8:	90 a9 00 00 	stw     r5,0(r9)
 2ec:	90 e9 00 04 	stw     r7,4(r9)
 2f0:	91 09 00 08 	stw     r8,8(r9)
 2f4:	91 49 00 0c 	stw     r10,12(r9)

With 16k pages, only the first entry is used by the kernel, so no need
to adapt the address of other entries. Only duplicate the first entry
for hardware.

Now it is:

 2cc:	39 40 00 00 	li      r10,0
 2d0:	91 49 00 00 	stw     r10,0(r9)
 2d4:	91 49 00 04 	stw     r10,4(r9)
 2d8:	91 49 00 08 	stw     r10,8(r9)
 2dc:	91 49 00 0c 	stw     r10,12(r9)

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
 arch/powerpc/include/asm/nohash/32/pgtable.h | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/include/asm/nohash/32/pgtable.h b/arch/powerpc/include/asm/nohash/32/pgtable.h
index 9091e4904a6b..981e414bdeef 100644
--- a/arch/powerpc/include/asm/nohash/32/pgtable.h
+++ b/arch/powerpc/include/asm/nohash/32/pgtable.h
@@ -256,8 +256,14 @@ static inline pte_basic_t pte_update(struct mm_struct *mm, unsigned long addr, p
 
 	num = number_of_cells_per_pte(pmd, new, huge);
 
-	for (i = 0; i < num; i++, entry++, new += SZ_4K)
-		*entry = new;
+	for (i = 0; i < num; i += PAGE_SIZE / SZ_4K, new += PAGE_SIZE) {
+		*entry++ = new;
+		if (IS_ENABLED(CONFIG_PPC_16K_PAGES) && num != 1) {
+			*entry++ = new;
+			*entry++ = new;
+			*entry++ = new;
+		}
+	}
 
 	return old;
 }
-- 
2.37.1

Re: [PATCH] powerpc/8xx: Simplify pte_update() with 16k pages

[Michael Ellerman]

On Wed, 28 Sep 2022 08:29:00 +0200, Christophe Leroy wrote:
> While looking at code generated for code patching, I saw that
> pte_clear generated:
> 
>  2d8:	38 a0 00 00 	li      r5,0
>  2dc:	38 e0 10 00 	li      r7,4096
>  2e0:	39 00 20 00 	li      r8,8192
>  2e4:	39 40 30 00 	li      r10,12288
>  2e8:	90 a9 00 00 	stw     r5,0(r9)
>  2ec:	90 e9 00 04 	stw     r7,4(r9)
>  2f0:	91 09 00 08 	stw     r8,8(r9)
>  2f4:	91 49 00 0c 	stw     r10,12(r9)
> 
> [...]

Applied to powerpc/next.

[1/1] powerpc/8xx: Simplify pte_update() with 16k pages
      https://git.kernel.org/powerpc/c/f2c45962cc618c12f69fd46e6ebc20b9cd7f15ac

cheers