riscv: mm: Add support for ZONE_DEVICE

ZONE_DEVICE pages need DEVMAP PTEs support to function
(ARCH_HAS_PTE_DEVMAP). Claim another RSW (reserved for software) bit
in the PTE for DEVMAP mark, add the corresponding helpers, and enable
ARCH_HAS_PTE_DEVMAP for riscv64.
Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Signed-off-by: Björn Töpel <bjorn@rivosinc.com>
Link: https://lore.kernel.org/r/20240605114100.315918-11-bjorn@kernel.orgSigned-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch/riscv/Kconfig

@@ -37,6 +37,7 @@ config RISCV
 	select ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
 	select ARCH_HAS_PMEM_API
 	select ARCH_HAS_PREPARE_SYNC_CORE_CMD
+	select ARCH_HAS_PTE_DEVMAP if 64BIT && MMU
 	select ARCH_HAS_PTE_SPECIAL
 	select ARCH_HAS_SET_DIRECT_MAP if MMU
 	select ARCH_HAS_SET_MEMORY if MMU

arch/riscv/include/asm/pgtable-64.h

@@ -398,4 +398,24 @@ static inline struct page *pgd_page(pgd_t pgd)
 #define p4d_offset p4d_offset
 p4d_t *p4d_offset(pgd_t *pgd, unsigned long address);
 
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+static inline int pte_devmap(pte_t pte);
+static inline pte_t pmd_pte(pmd_t pmd);
+
+static inline int pmd_devmap(pmd_t pmd)
+{
+	return pte_devmap(pmd_pte(pmd));
+}
+
+static inline int pud_devmap(pud_t pud)
+{
+	return 0;
+}
+
+static inline int pgd_devmap(pgd_t pgd)
+{
+	return 0;
+}
+#endif
+
 #endif /* _ASM_RISCV_PGTABLE_64_H */

arch/riscv/include/asm/pgtable-bits.h

@@ -19,6 +19,7 @@
 #define _PAGE_SOFT      (3 << 8)    /* Reserved for software */
 
 #define _PAGE_SPECIAL   (1 << 8)    /* RSW: 0x1 */
+#define _PAGE_DEVMAP    (1 << 9)    /* RSW, devmap */
 #define _PAGE_TABLE     _PAGE_PRESENT
 
 /*

arch/riscv/include/asm/pgtable.h

@@ -390,6 +390,13 @@ static inline int pte_special(pte_t pte)
 	return pte_val(pte) & _PAGE_SPECIAL;
 }
 
+#ifdef CONFIG_ARCH_HAS_PTE_DEVMAP
+static inline int pte_devmap(pte_t pte)
+{
+	return pte_val(pte) & _PAGE_DEVMAP;
+}
+#endif
+
 /* static inline pte_t pte_rdprotect(pte_t pte) */
 
 static inline pte_t pte_wrprotect(pte_t pte)
@@ -431,6 +438,11 @@ static inline pte_t pte_mkspecial(pte_t pte)
 	return __pte(pte_val(pte) | _PAGE_SPECIAL);
 }
 
+static inline pte_t pte_mkdevmap(pte_t pte)
+{
+	return __pte(pte_val(pte) | _PAGE_DEVMAP);
+}
+
 static inline pte_t pte_mkhuge(pte_t pte)
 {
 	return pte;
@@ -721,6 +733,11 @@ static inline pmd_t pmd_mkdirty(pmd_t pmd)
 	return pte_pmd(pte_mkdirty(pmd_pte(pmd)));
 }
 
+static inline pmd_t pmd_mkdevmap(pmd_t pmd)
+{
+	return pte_pmd(pte_mkdevmap(pmd_pte(pmd)));
+}
+
 static inline void set_pmd_at(struct mm_struct *mm, unsigned long addr,
 				pmd_t *pmdp, pmd_t pmd)
 {