[RFC PATCH V4 1/6] riscv: pgtable: Add custom protection_map init

[guoren]

From: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>

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. The patch prevents compile errors.

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@xxxxxxxxxxxxxxxxx>
Cc: Atish Patra <atish.patra@xxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Palmer Dabbelt <palmer@xxxxxxxxxxx>
---
 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 4f7b70ae7c31..3ab3730bee92 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -25,6 +25,7 @@ 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 if MMU
 	select ARCH_HAS_SET_MEMORY if MMU
@@ -201,6 +202,9 @@ 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 7cb4f391d106..975c7322d6c4 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -550,6 +550,26 @@ static void __init create_kernel_page_table(pgd_t *pgdir, uintptr_t map_size,
 }
 #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;
@@ -558,6 +578,8 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
 	pmd_t fix_bmap_spmd, fix_bmap_epmd;
 #endif
 
+	setup_protection_map();
+
 	kernel_map.virt_addr = KERNEL_LINK_ADDR;
 
 #ifdef CONFIG_XIP_KERNEL
diff --git a/mm/mmap.c b/mm/mmap.c
index 181a113b545d..6d74537122ad 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)
-- 
2.25.1