riscv: Support huge pfnmaps

Use RSW0 as the special bit for pmds and puds, just like for ptes.
Also define the {pte,pmd,pud}_pgprot helpers which were previously
missing and are needed for the follow_pfnmap APIs.

Signed-off-by: Andrew Bresticker <abrestic@rivosinc.com>
Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/r/20250108135700.2614848-1-abrestic@rivosinc.com
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>

Author: abrestic-rivos

arch/riscv/Kconfig

@@ -62,6 +62,7 @@ config RISCV
 	select ARCH_SUPPORTS_ATOMIC_RMW
 	select ARCH_SUPPORTS_CFI_CLANG
 	select ARCH_SUPPORTS_DEBUG_PAGEALLOC if MMU
+	select ARCH_SUPPORTS_HUGE_PFNMAP if TRANSPARENT_HUGEPAGE
 	select ARCH_SUPPORTS_HUGETLBFS if MMU
 	# LLD >= 14: https://github.com/llvm/llvm-project/issues/50505
 	select ARCH_SUPPORTS_LTO_CLANG if LLD_VERSION >= 140000

arch/riscv/include/asm/pgtable.h

@@ -341,6 +341,14 @@ static inline pte_t pfn_pte(unsigned long pfn, pgprot_t prot)
 
 #define mk_pte(page, prot)       pfn_pte(page_to_pfn(page), prot)
 
+#define pte_pgprot pte_pgprot
+static inline pgprot_t pte_pgprot(pte_t pte)
+{
+	unsigned long pfn = pte_pfn(pte);
+
+	return __pgprot(pte_val(pfn_pte(pfn, __pgprot(0))) ^ pte_val(pte));
+}
+
 static inline int pte_present(pte_t pte)
 {
 	return (pte_val(pte) & (_PAGE_PRESENT | _PAGE_PROT_NONE));
@@ -674,6 +682,11 @@ static inline pmd_t pte_pmd(pte_t pte)
 	return __pmd(pte_val(pte));
 }
 
+static inline pud_t pte_pud(pte_t pte)
+{
+	return __pud(pte_val(pte));
+}
+
 static inline pmd_t pmd_mkhuge(pmd_t pmd)
 {
 	return pmd;
@@ -699,6 +712,18 @@ static inline unsigned long pud_pfn(pud_t pud)
 	return ((__pud_to_phys(pud) & PUD_MASK) >> PAGE_SHIFT);
 }
 
+#define pmd_pgprot pmd_pgprot
+static inline pgprot_t pmd_pgprot(pmd_t pmd)
+{
+	return pte_pgprot(pmd_pte(pmd));
+}
+
+#define pud_pgprot pud_pgprot
+static inline pgprot_t pud_pgprot(pud_t pud)
+{
+	return pte_pgprot(pud_pte(pud));
+}
+
 static inline pmd_t pmd_modify(pmd_t pmd, pgprot_t newprot)
 {
 	return pte_pmd(pte_modify(pmd_pte(pmd), newprot));
@@ -768,6 +793,30 @@ static inline pmd_t pmd_mkdevmap(pmd_t pmd)
 	return pte_pmd(pte_mkdevmap(pmd_pte(pmd)));
 }
 
+#ifdef CONFIG_ARCH_SUPPORTS_PMD_PFNMAP
+static inline bool pmd_special(pmd_t pmd)
+{
+	return pte_special(pmd_pte(pmd));
+}
+
+static inline pmd_t pmd_mkspecial(pmd_t pmd)
+{
+	return pte_pmd(pte_mkspecial(pmd_pte(pmd)));
+}
+#endif
+
+#ifdef CONFIG_ARCH_SUPPORTS_PUD_PFNMAP
+static inline bool pud_special(pud_t pud)
+{
+	return pte_special(pud_pte(pud));
+}
+
+static inline pud_t pud_mkspecial(pud_t pud)
+{
+	return pte_pud(pte_mkspecial(pud_pte(pud)));
+}
+#endif
+
 static inline void set_pmd_at(struct mm_struct *mm, unsigned long addr,
 				pmd_t *pmdp, pmd_t pmd)
 {