[RFC PATCH 05/10] mm: introduce and use vma_filebacked_address()

[Lorenzo Stoakes]

In cases where we know that the VMA is file-backed, use
vma_filebacked_address() rather than vma_address().

This lays the foundation for using the virtual page offset for anonymous
VMAs via vma_anon_address().

Also add an assert to ensure that the VMA whose address is required is not
anonymous.

No functional change intended.

Signed-off-by: Lorenzo Stoakes <ljs@xxxxxxxxxx>
---
 mm/internal.h        | 18 ++++++++++++++++++
 mm/memory-failure.c  |  4 ++--
 mm/page_vma_mapped.c |  6 +++++-
 mm/rmap.c            | 10 ++++++----
 4 files changed, 31 insertions(+), 7 deletions(-)

diff --git a/mm/internal.h b/mm/internal.h
index 8689f560854f..f1e7e6256b4c 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -1244,6 +1244,24 @@ static inline unsigned long __vma_address(const struct vm_area_struct *vma,
 	return address;
 }
 
+/**
+ * vma_filebacked_address - Find the virtual address a file-backed page range is
+ * mapped at.
+ * @vma: The vma which maps this object.
+ * @pgoff: The page offset within its object.
+ * @nr_pages: The number of pages to consider.
+ *
+ * Returns: If any page in this range is mapped by this VMA, return the first
+ * address where any of these pages appear.  Otherwise, return -EFAULT.
+ */
+static inline unsigned long vma_filebacked_address(const struct vm_area_struct *vma,
+		pgoff_t pgoff, unsigned long nr_pages)
+{
+	VM_WARN_ON_ONCE(vma_is_anonymous(vma));
+
+	return __vma_address(vma, pgoff, vma_start_pgoff(vma), nr_pages);
+}
+
 /**
  * vma_address - Find the virtual address a page range is mapped at.
  * @vma: The vma which maps this object.
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index cbdec52b6d23..5b7cf2291b09 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -608,7 +608,7 @@ static void add_to_kill_fsdax(struct task_struct *tsk, const struct page *p,
 			      struct vm_area_struct *vma,
 			      struct list_head *to_kill, pgoff_t pgoff)
 {
-	unsigned long addr = vma_address(vma, pgoff, 1);
+	unsigned long addr = vma_filebacked_address(vma, pgoff, 1);
 	__add_to_kill(tsk, p, vma, to_kill, addr);
 }
 
@@ -2207,7 +2207,7 @@ static void add_to_kill_pgoff(struct task_struct *tsk,
 	}
 
 	/* Check for pgoff not backed by struct page */
-	tk->addr = vma_address(vma, pgoff, 1);
+	tk->addr = vma_filebacked_address(vma, pgoff, 1);
 	tk->size_shift = PAGE_SHIFT;
 
 	if (tk->addr == -EFAULT)
diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
index 2ccbabfb2cc1..eff619180e84 100644
--- a/mm/page_vma_mapped.c
+++ b/mm/page_vma_mapped.c
@@ -347,6 +347,7 @@ unsigned long page_mapped_in_vma(const struct page *page,
 		struct vm_area_struct *vma)
 {
 	const struct folio *folio = page_folio(page);
+	const pgoff_t pgoff = page_pgoff(folio, page);
 	struct page_vma_mapped_walk pvmw = {
 		.pfn = page_to_pfn(page),
 		.nr_pages = 1,
@@ -354,7 +355,10 @@ unsigned long page_mapped_in_vma(const struct page *page,
 		.flags = PVMW_SYNC,
 	};
 
-	pvmw.address = vma_address(vma, page_pgoff(folio, page), 1);
+	if (folio_test_anon(folio))
+		pvmw.address = vma_address(vma, pgoff, 1);
+	else
+		pvmw.address = vma_filebacked_address(vma, pgoff, 1);
 	if (pvmw.address == -EFAULT)
 		goto out;
 	if (!page_vma_mapped_walk(&pvmw))
diff --git a/mm/rmap.c b/mm/rmap.c
index 183603813255..0bdb65852222 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -865,14 +865,15 @@ unsigned long page_address_in_vma(const struct folio *folio,
 		if (!vma->anon_vma || !anon_vma ||
 		    vma->anon_vma->root != anon_vma->root)
 			return -EFAULT;
+		/* KSM folios don't reach here because of the !anon_vma check */
+		return vma_address(vma, page_pgoff(folio, page), 1);
 	} else if (!vma->vm_file) {
 		return -EFAULT;
 	} else if (vma->vm_file->f_mapping != folio->mapping) {
 		return -EFAULT;
 	}
 
-	/* KSM folios don't reach here because of the !anon_vma check */
-	return vma_address(vma, page_pgoff(folio, page), 1);
+	return vma_filebacked_address(vma, page_pgoff(folio, page), 1);
 }
 
 /*
@@ -1321,7 +1322,7 @@ int pfn_mkclean_range(unsigned long pfn, unsigned long nr_pages, pgoff_t pgoff,
 	if (invalid_mkclean_vma(vma, NULL))
 		return 0;
 
-	pvmw.address = vma_address(vma, pgoff, nr_pages);
+	pvmw.address = vma_filebacked_address(vma, pgoff, nr_pages);
 	VM_BUG_ON_VMA(pvmw.address == -EFAULT, vma);
 
 	return page_vma_mkclean_one(&pvmw);
@@ -3051,7 +3052,8 @@ static void __rmap_walk_file(struct folio *folio, struct address_space *mapping,
 	}
 lookup:
 	mapping_interval_tree_foreach(vma, mapping, pgoff_start, pgoff_end) {
-		unsigned long address = vma_address(vma, pgoff_start, nr_pages);
+		unsigned long address = vma_filebacked_address(vma, pgoff_start,
+							       nr_pages);
 
 		VM_BUG_ON_VMA(address == -EFAULT, vma);
 		cond_resched();
-- 
2.54.0