[PATCH v5 6/9] mm: Use common huge_ptep_get_and_clear() function for riscv/arm64

[Alexandre Ghiti <alexghiti@rivosinc.com>]

After some adjustments, both architectures have the same implementation
so move it to the generic code.

Note that get_clear_contig() function is duplicated in the generic and
the arm64 code because it is still used by some arm64 functions that
will, in the next commits, be moved to the generic code. Once all have
been moved, the arm64 version will be removed.

Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
---
 arch/arm64/include/asm/hugetlb.h |  3 --
 arch/arm64/mm/hugetlbpage.c      | 10 -------
 arch/riscv/include/asm/hugetlb.h |  5 ----
 arch/riscv/mm/hugetlbpage.c      | 15 ----------
 include/linux/hugetlb_contpte.h  |  5 ++++
 mm/hugetlb_contpte.c             | 51 ++++++++++++++++++++++++++++++++
 6 files changed, 56 insertions(+), 33 deletions(-)

diff --git a/arch/arm64/include/asm/hugetlb.h b/arch/arm64/include/asm/hugetlb.h
index ed75631ad63c..9b1c25775bea 100644
--- a/arch/arm64/include/asm/hugetlb.h
+++ b/arch/arm64/include/asm/hugetlb.h
@@ -39,9 +39,6 @@ pte_t arch_make_huge_pte(pte_t entry, unsigned int shift, vm_flags_t flags);
 extern int huge_ptep_set_access_flags(struct vm_area_struct *vma,
 				      unsigned long addr, pte_t *ptep,
 				      pte_t pte, int dirty);
-#define __HAVE_ARCH_HUGE_PTEP_GET_AND_CLEAR
-extern pte_t huge_ptep_get_and_clear(struct mm_struct *mm, unsigned long addr,
-				     pte_t *ptep, unsigned long sz);
 #define __HAVE_ARCH_HUGE_PTEP_SET_WRPROTECT
 extern void huge_ptep_set_wrprotect(struct mm_struct *mm,
 				    unsigned long addr, pte_t *ptep);
diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c
index 99728b02a3ca..62a66ce2b2fe 100644
--- a/arch/arm64/mm/hugetlbpage.c
+++ b/arch/arm64/mm/hugetlbpage.c
@@ -260,16 +260,6 @@ pte_t arch_make_huge_pte(pte_t entry, unsigned int shift, vm_flags_t flags)
 	return entry;
 }
 
-pte_t huge_ptep_get_and_clear(struct mm_struct *mm, unsigned long addr,
-			      pte_t *ptep, unsigned long sz)
-{
-	int ncontig;
-	size_t pgsize;
-
-	ncontig = arch_contpte_get_num_contig(ptep, sz, &pgsize);
-	return get_clear_contig(mm, addr, ptep, pgsize, ncontig);
-}
-
 /*
  * huge_ptep_set_access_flags will update access flags (dirty, accesssed)
  * and write permission.
diff --git a/arch/riscv/include/asm/hugetlb.h b/arch/riscv/include/asm/hugetlb.h
index 467bc30c2153..0fbb6b19df79 100644
--- a/arch/riscv/include/asm/hugetlb.h
+++ b/arch/riscv/include/asm/hugetlb.h
@@ -20,11 +20,6 @@ bool arch_hugetlb_migration_supported(struct hstate *h);
 #endif
 
 #ifdef CONFIG_RISCV_ISA_SVNAPOT
-#define __HAVE_ARCH_HUGE_PTEP_GET_AND_CLEAR
-pte_t huge_ptep_get_and_clear(struct mm_struct *mm,
-			      unsigned long addr, pte_t *ptep,
-			      unsigned long sz);
-
 #define __HAVE_ARCH_HUGE_PTEP_CLEAR_FLUSH
 pte_t huge_ptep_clear_flush(struct vm_area_struct *vma,
 			    unsigned long addr, pte_t *ptep);
diff --git a/arch/riscv/mm/hugetlbpage.c b/arch/riscv/mm/hugetlbpage.c
index fe82284c3dc4..87168123d4a2 100644
--- a/arch/riscv/mm/hugetlbpage.c
+++ b/arch/riscv/mm/hugetlbpage.c
@@ -203,21 +203,6 @@ int huge_ptep_set_access_flags(struct vm_area_struct *vma,
 	return true;
 }
 
-pte_t huge_ptep_get_and_clear(struct mm_struct *mm,
-			      unsigned long addr,
-			      pte_t *ptep, unsigned long sz)
-{
-	pte_t orig_pte = ptep_get(ptep);
-	int pte_num;
-
-	if (!pte_napot(orig_pte))
-		return ptep_get_and_clear(mm, addr, ptep);
-
-	pte_num = arch_contpte_get_num_contig(ptep, sz, NULL);
-
-	return get_clear_contig(mm, addr, ptep, pte_num);
-}
-
 void huge_ptep_set_wrprotect(struct mm_struct *mm,
 			     unsigned long addr,
 			     pte_t *ptep)
diff --git a/include/linux/hugetlb_contpte.h b/include/linux/hugetlb_contpte.h
index e6aa9befa78c..1c8f46ff95ea 100644
--- a/include/linux/hugetlb_contpte.h
+++ b/include/linux/hugetlb_contpte.h
@@ -18,4 +18,9 @@ extern void set_huge_pte_at(struct mm_struct *mm,
 extern void huge_pte_clear(struct mm_struct *mm, unsigned long addr,
 			   pte_t *ptep, unsigned long sz);
 
+#define __HAVE_ARCH_HUGE_PTEP_GET_AND_CLEAR
+extern pte_t huge_ptep_get_and_clear(struct mm_struct *mm,
+				     unsigned long addr, pte_t *ptep,
+				     unsigned long sz);
+
 #endif /* _LINUX_HUGETLB_CONTPTE_H */
diff --git a/mm/hugetlb_contpte.c b/mm/hugetlb_contpte.c
index e881b302dd63..82f49eb79ffb 100644
--- a/mm/hugetlb_contpte.c
+++ b/mm/hugetlb_contpte.c
@@ -98,3 +98,54 @@ void huge_pte_clear(struct mm_struct *mm, unsigned long addr,
 	for (i = 0; i < ncontig; i++, addr += pgsize, ptep++)
 		__pte_clear(mm, addr, ptep);
 }
+
+/*
+ * ARM: Changing some bits of contiguous entries requires us to follow a
+ * Break-Before-Make approach, breaking the whole contiguous set
+ * before we can change any entries. See ARM DDI 0487A.k_iss10775,
+ * "Misprogramming of the Contiguous bit", page D4-1762.
+ *
+ * RISCV: When dealing with NAPOT mappings, the privileged specification
+ * indicates that "if an update needs to be made, the OS generally should first
+ * mark all of the PTEs invalid, then issue SFENCE.VMA instruction(s) covering
+ * all 4 KiB regions within the range, [...] then update the PTE(s), as
+ * described in Section 4.2.1.". That's the equivalent of the Break-Before-Make
+ * approach used by arm64.
+ *
+ * This helper performs the break step.
+ */
+static pte_t get_clear_contig(struct mm_struct *mm,
+			     unsigned long addr,
+			     pte_t *ptep,
+			     unsigned long pgsize,
+			     unsigned long ncontig)
+{
+	pte_t pte, tmp_pte;
+	bool present;
+
+	pte = __ptep_get_and_clear(mm, addr, ptep);
+	present = pte_present(pte);
+	while (--ncontig) {
+		ptep++;
+		addr += pgsize;
+		tmp_pte = __ptep_get_and_clear(mm, addr, ptep);
+		if (present) {
+			if (pte_dirty(tmp_pte))
+				pte = pte_mkdirty(pte);
+			if (pte_young(tmp_pte))
+				pte = pte_mkyoung(pte);
+		}
+	}
+	return pte;
+}
+
+pte_t huge_ptep_get_and_clear(struct mm_struct *mm,
+			      unsigned long addr, pte_t *ptep, unsigned long sz)
+{
+	int ncontig;
+	size_t pgsize;
+
+	ncontig = arch_contpte_get_num_contig(ptep, sz, &pgsize);
+
+	return get_clear_contig(mm, addr, ptep, pgsize, ncontig);
+}
-- 
2.39.2