linux-kernel - [PATCH v2 4/4] arm: replace vector mem type with read-only type

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Date:   Fri, 23 Oct 2020 17:14:37 +0800
From:   Miles Chen <miles.chen@...iatek.com>
To:     Catalin Marinas <catalin.marinas@....com>,
        Russell King <linux@...linux.org.uk>,
        Minchan Kim <minchan@...nel.org>
CC:     <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-mediatek@...ts.infradead.org>, <wsd_upstream@...iatek.com>,
        Miles Chen <miles.chen@...iatek.com>,
        Suren Baghdasaryan <surenb@...gle.com>
Subject: [PATCH v2 4/4] arm: replace vector mem type with read-only type

Since kernel no longer writes to the vector, try to replace
the vector mem type with read-only type and remove L_PTE_MT_VECTORS.

from Catalin in [1]:
"
> I don't think this matters since the kernel no longer writes to the
> vectors page at run-time but it needs cleaning up a bit (and testing in
> case I missed something). IOW, do we still need a dedicated mapping type
> for the vectors or we can simply use the read-only user page attributes?
"

[1] https://lore.kernel.org/patchwork/patch/986574/

Cc: Russell King <linux@...linux.org.uk>
Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Minchan Kim <minchan@...nel.org>
Cc: Suren Baghdasaryan <surenb@...gle.com>
Signed-off-by: Miles Chen <miles.chen@...iatek.com>
---
 arch/arm/include/asm/pgtable-2level.h | 1 -
 arch/arm/mm/mmu.c                     | 7 +++----
 arch/arm/mm/proc-macros.S             | 2 +-
 3 files changed, 4 insertions(+), 6 deletions(-)

diff --git a/arch/arm/include/asm/pgtable-2level.h b/arch/arm/include/asm/pgtable-2level.h
index 385e7a32394e..438359d3675f 100644
--- a/arch/arm/include/asm/pgtable-2level.h
+++ b/arch/arm/include/asm/pgtable-2level.h
@@ -163,7 +163,6 @@
 #define L_PTE_MT_WRITETHROUGH	(_AT(pteval_t, 0x02) << 2)	/* 0010 */
 #define L_PTE_MT_WRITEBACK	(_AT(pteval_t, 0x03) << 2)	/* 0011 */
 #define L_PTE_MT_DEV_SHARED	(_AT(pteval_t, 0x04) << 2)	/* 0100 */
-#define L_PTE_MT_VECTORS	(_AT(pteval_t, 0x05) << 2)	/* 0101 */
 #define L_PTE_MT_MINICACHE	(_AT(pteval_t, 0x06) << 2)	/* 0110 (sa1100, xscale) */
 #define L_PTE_MT_WRITEALLOC	(_AT(pteval_t, 0x07) << 2)	/* 0111 */
 #if defined(CONFIG_CPU_V7) || defined(CONFIG_CPU_V6) || defined(CONFIG_CPU_V6K)
diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
index ab69250a86bc..0b6b377e2cce 100644
--- a/arch/arm/mm/mmu.c
+++ b/arch/arm/mm/mmu.c
@@ -536,12 +536,11 @@ static void __init build_mem_type_table(void)
 
 #ifndef CONFIG_ARM_LPAE
 	/*
-	 * We don't use domains on ARMv6 (since this causes problems with
-	 * v6/v7 kernels), so we must use a separate memory type for user
-	 * r/o, kernel r/w to map the vectors page.
+	 * We no longer write to the vector pages ar run-time, to
+	 * use read-only user page attribute for vector.
 	 */
 	if (cpu_arch == CPU_ARCH_ARMv6)
-		vecs_pgprot |= L_PTE_MT_VECTORS;
+		vecs_pgprot |= L_PTE_RDONLY;
 
 	/*
 	 * Check is it with support for the PXN bit
diff --git a/arch/arm/mm/proc-macros.S b/arch/arm/mm/proc-macros.S
index dde1d6374250..f3e6551b4a7e 100644
--- a/arch/arm/mm/proc-macros.S
+++ b/arch/arm/mm/proc-macros.S
@@ -137,7 +137,7 @@
 	.long	PTE_CACHEABLE					@ L_PTE_MT_WRITETHROUGH
 	.long	PTE_CACHEABLE | PTE_BUFFERABLE			@ L_PTE_MT_WRITEBACK
 	.long	PTE_BUFFERABLE					@ L_PTE_MT_DEV_SHARED
-	.long	PTE_CACHEABLE | PTE_BUFFERABLE | PTE_EXT_APX	@ L_PTE_MT_VECTORS
+	.long	0x00						@ unused
 	.long	0x00						@ L_PTE_MT_MINICACHE (not present)
 	.long	PTE_EXT_TEX(1) | PTE_CACHEABLE | PTE_BUFFERABLE	@ L_PTE_MT_WRITEALLOC
 	.long	0x00						@ unused
-- 
2.18.0