[PATCH 2/4] mm: huge_mapping_get_va_aligned() helper

[Peter Xu]

Add this helper to allocate a VA that would be best to map huge mappings
that the system would support. It can be used in file's get_unmapped_area()
functions as long as proper max_pgoff will be provided so that core mm will
know the available range of pgoff to map in the future.

Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
---
 include/linux/huge_mm.h | 10 ++++++++-
 mm/huge_memory.c        | 46 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 55 insertions(+), 1 deletion(-)

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 2f190c90192d..59fdafb1034b 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -339,7 +339,8 @@ unsigned long thp_get_unmapped_area(struct file *filp, unsigned long addr,
 unsigned long thp_get_unmapped_area_vmflags(struct file *filp, unsigned long addr,
 		unsigned long len, unsigned long pgoff, unsigned long flags,
 		vm_flags_t vm_flags);
-
+unsigned long huge_mapping_get_va_aligned(struct file *filp, unsigned long addr,
+		unsigned long len, unsigned long pgoff, unsigned long flags);
 bool can_split_folio(struct folio *folio, int caller_pins, int *pextra_pins);
 int split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
 		unsigned int new_order);
@@ -543,6 +544,13 @@ thp_get_unmapped_area_vmflags(struct file *filp, unsigned long addr,
 	return 0;
 }
 
+static inline unsigned long
+huge_mapping_get_va_aligned(struct file *filp, unsigned long addr,
+		unsigned long len, unsigned long pgoff, unsigned long flags)
+{
+	return mm_get_unmapped_area(current->mm, filp, addr, len, pgoff, flags);
+}
+
 static inline bool
 can_split_folio(struct folio *folio, int caller_pins, int *pextra_pins)
 {
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 885b5845dbba..bc016b656dc7 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1161,6 +1161,52 @@ unsigned long thp_get_unmapped_area(struct file *filp, unsigned long addr,
 }
 EXPORT_SYMBOL_GPL(thp_get_unmapped_area);
 
+/**
+ * huge_mapping_get_va_aligned: best-effort VA allocation for huge mappings
+ *
+ * @filp: file target of the mmap() request
+ * @addr: hint address from mmap() request
+ * @len: len of the mmap() request
+ * @pgoff: file offset of the mmap() request
+ * @flags: flags of the mmap() request
+ *
+ * This function should normally be used by a driver's specific
+ * get_unmapped_area() handler to provide a huge-mapping friendly virtual
+ * address for a specific mmap() request.  The caller should pass in most
+ * of the parameters from the get_unmapped_area() request.
+ *
+ * Normally it means the caller's mmap() needs to also support any possible
+ * huge mappings the system supports.
+ *
+ * Return: a best-effort virtual address that will satisfy the most huge
+ * mappings for the result VMA to be mapped.
+ */
+unsigned long huge_mapping_get_va_aligned(struct file *filp, unsigned long addr,
+		unsigned long len, unsigned long pgoff, unsigned long flags)
+{
+	loff_t off = (loff_t)pgoff << PAGE_SHIFT;
+	unsigned long ret;
+
+	/* TODO: support continuous ptes/pmds */
+	if (IS_ENABLED(CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD) &&
+	    len >= PUD_SIZE) {
+		ret = mm_get_unmapped_area_aligned(filp, addr, len, off, flags,
+						   PUD_SIZE, 0);
+		if (ret)
+			return ret;
+	}
+
+	if (len >= PMD_SIZE) {
+		ret = mm_get_unmapped_area_aligned(filp, addr, len, off, flags,
+						   PMD_SIZE, 0);
+		if (ret)
+			return ret;
+	}
+
+	return mm_get_unmapped_area(current->mm, filp, addr, len, pgoff, flags);
+}
+EXPORT_SYMBOL_GPL(huge_mapping_get_va_aligned);
+
 static struct folio *vma_alloc_anon_folio_pmd(struct vm_area_struct *vma,
 		unsigned long addr)
 {
-- 
2.49.0