linux-kernel - [PATCH v4 16/16] powerpc/kconfig: make _etext and data areas alignment configurable on 8xx

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Message-Id: <0e333d8e1d35eefb125cb9e72f58e0703b10bc1a.1550692943.git.christophe.leroy@c-s.fr>
Date:   Thu, 21 Feb 2019 08:05:04 +0000 (UTC)
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>, j.neuschaefer@....net
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH v4 16/16] powerpc/kconfig: make _etext and data areas
 alignment configurable on 8xx

On 8xx, large pages (512kb or 8M) are used to map kernel linear
memory. Aligning to 8M reduces TLB misses as only 8M pages are used
in that case. We make 8M the default for data.

This patchs allows the user to do it via Kconfig.

Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
---
 arch/powerpc/Kconfig           | 18 +++++++++++++++---
 arch/powerpc/kernel/head_8xx.S |  4 ++--
 2 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 271f13ac23d4..447b86ea4815 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -729,7 +729,8 @@ config THREAD_SHIFT
 	  want. Only change this if you know what you are doing.
 
 config ETEXT_SHIFT_BOOL
-	bool "Set custom etext alignment" if STRICT_KERNEL_RWX && PPC_BOOK3S_32
+	bool "Set custom etext alignment" if STRICT_KERNEL_RWX && \
+					     (PPC_BOOK3S_32 || PPC_8xx)
 	depends on ADVANCED_OPTIONS
 	help
 	  This option allows you to set the kernel end of text alignment. When
@@ -741,6 +742,7 @@ config ETEXT_SHIFT_BOOL
 config ETEXT_SHIFT
 	int "_etext shift" if ETEXT_SHIFT_BOOL
 	range 17 28 if STRICT_KERNEL_RWX && PPC_BOOK3S_32
+	range 19 23 if STRICT_KERNEL_RWX && PPC_8xx
 	default 17 if STRICT_KERNEL_RWX && PPC_BOOK3S_32
 	default 19 if STRICT_KERNEL_RWX && PPC_8xx
 	default PPC_PAGE_SHIFT
@@ -748,8 +750,13 @@ config ETEXT_SHIFT
 	  On Book3S 32 (603+), IBATs are used to map kernel text.
 	  Smaller is the alignment, greater is the number of necessary IBATs.
 
+	  On 8xx, large pages (512kb or 8M) are used to map kernel linear
+	  memory. Aligning to 8M reduces TLB misses as only 8M pages are used
+	  in that case.
+
 config DATA_SHIFT_BOOL
-	bool "Set custom data alignment" if STRICT_KERNEL_RWX && PPC_BOOK3S_32
+	bool "Set custom data alignment" if STRICT_KERNEL_RWX && \
+					    (PPC_BOOK3S_32 || PPC_8xx)
 	depends on ADVANCED_OPTIONS
 	help
 	  This option allows you to set the kernel data alignment. When
@@ -762,13 +769,18 @@ config DATA_SHIFT
 	int "Data shift" if DATA_SHIFT_BOOL
 	default 24 if STRICT_KERNEL_RWX && PPC64
 	range 17 28 if STRICT_KERNEL_RWX && PPC_BOOK3S_32
+	range 19 23 if STRICT_KERNEL_RWX && PPC_8xx
 	default 22 if STRICT_KERNEL_RWX && PPC_BOOK3S_32
-	default 19 if STRICT_KERNEL_RWX && PPC_8xx
+	default 23 if STRICT_KERNEL_RWX && PPC_8xx
 	default PPC_PAGE_SHIFT
 	help
 	  On Book3S 32 (603+), DBATs are used to map kernel text and rodata RO.
 	  Smaller is the alignment, greater is the number of necessary DBATs.
 
+	  On 8xx, large pages (512kb or 8M) are used to map kernel linear
+	  memory. Aligning to 8M reduces TLB misses as only 8M pages are used
+	  in that case.
+
 config FORCE_MAX_ZONEORDER
 	int "Maximum zone order"
 	range 8 9 if PPC64 && PPC_64K_PAGES
diff --git a/arch/powerpc/kernel/head_8xx.S b/arch/powerpc/kernel/head_8xx.S
index 29c9289bc1d4..b10dc01690fc 100644
--- a/arch/powerpc/kernel/head_8xx.S
+++ b/arch/powerpc/kernel/head_8xx.S
@@ -416,7 +416,7 @@ InstructionTLBMiss:
 #ifndef CONFIG_PIN_TLB_TEXT
 ITLBMissLinear:
 	mtcr	r11
-#ifdef CONFIG_STRICT_KERNEL_RWX
+#if defined(CONFIG_STRICT_KERNEL_RWX) && CONFIG_ETEXT_SHIFT < 23
 	patch_site	0f, patch__itlbmiss_linmem_top8
 
 	mfspr	r10, SPRN_SRR0
@@ -537,7 +537,7 @@ DTLBMissIMMR:
 DTLBMissLinear:
 	mtcr	r11
 	rlwinm	r10, r10, 20, 0x0f800000	/* 8xx supports max 256Mb RAM */
-#ifdef CONFIG_STRICT_KERNEL_RWX
+#if defined(CONFIG_STRICT_KERNEL_RWX) && CONFIG_DATA_SHIFT < 23
 	patch_site	0f, patch__dtlbmiss_romem_top8
 
 0:	subis	r11, r10, (PAGE_OFFSET - 0x80000000)@ha
-- 
2.13.3