[PATCH RFC 1/2] pgtable: add pte_clrhuge() implementation for arm64 and riscv

[Yin Tirui <yintirui@huawei.com>]

Add pte_clrhuge() helper function for architectures that enable
ARCH_SUPPORTS_HUGE_PFNMAP to clear huge page attributes from PTE
entries.

This function provides the inverse operation of pte_mkhuge() and will
be needed for upcoming huge page splitting, where PTE entries derived
from huge page mappings need to have their huge page attributes cleared.

Future work will refactor pfn_pte() to automatically filter huge bits,
removing the need for pte_clrhuge() across all architectures.

Signed-off-by: Yin Tirui <yintirui@huawei.com>
---
 arch/arm64/include/asm/pgtable.h | 8 ++++++++
 arch/riscv/include/asm/pgtable.h | 5 +++++
 2 files changed, 13 insertions(+)

diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index abd2dee416b3..244755bad46f 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -366,6 +366,14 @@ static inline pte_t pte_mkinvalid(pte_t pte)
 	return pte;
 }
 
+static inline pte_t pte_clrhuge(pte_t pte)
+{
+	pteval_t mask = PTE_TYPE_MASK & ~PTE_VALID;
+	pteval_t val = PTE_TYPE_PAGE & ~PTE_VALID;
+
+	return __pte((pte_val(pte) & ~mask) | val);
+}
+
 static inline pmd_t pmd_mkcont(pmd_t pmd)
 {
 	return __pmd(pmd_val(pmd) | PMD_SECT_CONT);
diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
index 815067742939..b0a20ddf780a 100644
--- a/arch/riscv/include/asm/pgtable.h
+++ b/arch/riscv/include/asm/pgtable.h
@@ -455,6 +455,11 @@ static inline pte_t pte_mkhuge(pte_t pte)
 	return pte;
 }
 
+static inline pte_t pte_clrhuge(pte_t pte)
+{
+	return pte;
+}
+
 #ifdef CONFIG_RISCV_ISA_SVNAPOT
 #define pte_leaf_size(pte)	(pte_napot(pte) ?				\
 					napot_cont_size(napot_cont_order(pte)) :\
-- 
2.43.0