linux-kernel - [PATCH v1 4/8] powerpc/32s: Don't use SPRN_SPRG_PGDIR in hash

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Message-Id: <4adca19b7120cdf619956768ed09e74fc6a558f3.1606285014.git.christophe.leroy@csgroup.eu>
Date:   Wed, 25 Nov 2020 07:10:49 +0000 (UTC)
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH v1 4/8] powerpc/32s: Don't use SPRN_SPRG_PGDIR in hash_page

SPRN_SPRG_PGDIR is there mainly to speedup SW TLB miss handlers
for powerpc 603.

We need to free SPRN_SPRG2 to reduce the mess with CONFIG_VMAP_STACK.

In hash_page(), reading PGDIR from thread_struct will be in the noise
performance wise.

Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
---
 arch/powerpc/mm/book3s32/hash_low.S | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/arch/powerpc/mm/book3s32/hash_low.S b/arch/powerpc/mm/book3s32/hash_low.S
index 48415c857d80..aca353d1c5f4 100644
--- a/arch/powerpc/mm/book3s32/hash_low.S
+++ b/arch/powerpc/mm/book3s32/hash_low.S
@@ -65,13 +65,14 @@ _GLOBAL(hash_page)
 	/* Get PTE (linux-style) and check access */
 	lis	r0, TASK_SIZE@h		/* check if kernel address */
 	cmplw	0,r4,r0
+	mfspr	r8,SPRN_SPRG_THREAD	/* current task's THREAD (phys) */
 	ori	r3,r3,_PAGE_USER|_PAGE_PRESENT /* test low addresses as user */
-	mfspr	r5, SPRN_SPRG_PGDIR	/* phys page-table root */
+	lwz	r5,PGDIR(r8)		/* virt page-table root */
 	blt+	112f			/* assume user more likely */
-	lis	r5, (swapper_pg_dir - PAGE_OFFSET)@ha	/* if kernel address, use */
-	addi	r5 ,r5 ,(swapper_pg_dir - PAGE_OFFSET)@l	/* kernel page table */
+	lis	r5,swapper_pg_dir@ha	/* if kernel address, use */
+	addi	r5,r5,swapper_pg_dir@l	/* kernel page table */
 	rlwimi	r3,r9,32-12,29,29	/* MSR_PR -> _PAGE_USER */
-112:
+112:	tophys(r5, r5)
 #ifndef CONFIG_PTE_64BIT
 	rlwimi	r5,r4,12,20,29		/* insert top 10 bits of address */
 	lwz	r8,0(r5)		/* get pmd entry */
-- 
2.25.0