[RFC PATCH v3 1/2] riscv: pgtable: Add custom protection_map init

[guoren@kernel.org]

From: Guo Ren <guoren@linux.alibaba.com>

Some RISC-V CPU vendors have defined their own PTE attributes to
solve non-coherent DMA bus problems. That makes _P/SXXX definitions
contain global variables which could be initialized at the early
boot stage before setup_vm.

This patch is similar to 316d097c4cd4  (x86/pti: Filter at
vma->vm_page_prot population) which give a choice for arch custom
implementation.

Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
---
 arch/riscv/Kconfig   |  4 ++++
 arch/riscv/mm/init.c | 22 ++++++++++++++++++++++
 mm/mmap.c            |  4 ++++
 3 files changed, 30 insertions(+)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index be3d7e2..5327f6f 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -29,6 +29,7 @@ config RISCV
 	select ARCH_HAS_GIGANTIC_PAGE
 	select ARCH_HAS_KCOV
 	select ARCH_HAS_MMIOWB
+	select ARCH_HAS_PROTECTION_MAP_INIT
 	select ARCH_HAS_PTE_SPECIAL
 	select ARCH_HAS_SET_DIRECT_MAP
 	select ARCH_HAS_SET_MEMORY
@@ -207,6 +208,9 @@ config GENERIC_HWEIGHT
 config FIX_EARLYCON_MEM
 	def_bool MMU
 
+config ARCH_HAS_PROTECTION_MAP_INIT
+	def_bool y
+
 config PGTABLE_LEVELS
 	int
 	default 3 if 64BIT
diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index 9c4eabb..4b55046 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -554,6 +554,26 @@ static void __init create_kernel_page_table(pgd_t *pgdir, uintptr_t map_size, bo
 }
 #endif
 
+static void __init setup_protection_map(void)
+{
+	protection_map[0]  = __P000;
+	protection_map[1]  = __P001;
+	protection_map[2]  = __P010;
+	protection_map[3]  = __P011;
+	protection_map[4]  = __P100;
+	protection_map[5]  = __P101;
+	protection_map[6]  = __P110;
+	protection_map[7]  = __P111;
+	protection_map[8]  = __S000;
+	protection_map[9]  = __S001;
+	protection_map[10] = __S010;
+	protection_map[11] = __S011;
+	protection_map[12] = __S100;
+	protection_map[13] = __S101;
+	protection_map[14] = __S110;
+	protection_map[15] = __S111;
+}
+
 asmlinkage void __init setup_vm(uintptr_t dtb_pa)
 {
 	uintptr_t __maybe_unused pa;
@@ -562,6 +582,8 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
 	pmd_t fix_bmap_spmd, fix_bmap_epmd;
 #endif
 
+	setup_protection_map();
+
 #ifdef CONFIG_XIP_KERNEL
 	xiprom = (uintptr_t)CONFIG_XIP_PHYS_ADDR;
 	xiprom_sz = (uintptr_t)(&_exiprom) - (uintptr_t)(&_xiprom);
diff --git a/mm/mmap.c b/mm/mmap.c
index 0584e54..0a86059 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -100,10 +100,14 @@ static void unmap_region(struct mm_struct *mm,
  *								w: (no) no
  *								x: (yes) yes
  */
+#ifdef CONFIG_ARCH_HAS_PROTECTION_MAP_INIT
+pgprot_t protection_map[16] __ro_after_init;
+#else
 pgprot_t protection_map[16] __ro_after_init = {
 	__P000, __P001, __P010, __P011, __P100, __P101, __P110, __P111,
 	__S000, __S001, __S010, __S011, __S100, __S101, __S110, __S111
 };
+#endif
 
 #ifndef CONFIG_ARCH_HAS_FILTER_PGPROT
 static inline pgprot_t arch_filter_pgprot(pgprot_t prot)
-- 
2.7.4