linux-kernel - [PATCH] powerpc/8xx: Simplify pte

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Message-Id: <65f76300de07091a59a042a3db2d0ce9b939a05c.1664346532.git.christophe.leroy@csgroup.eu>
Date:   Wed, 28 Sep 2022 08:29:00 +0200
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>
Cc:     Christophe Leroy <christophe.leroy@...roup.eu>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH] powerpc/8xx: Simplify pte_update() with 16k pages

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@...roup.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