[RFC v2 PATCH 11/17] mm: Split __wp_page_copy_user() into 2 variants

[Ryan Roberts <ryan.roberts@arm.com>]

We will soon support CoWing large folios, so will need support for
copying a contiguous range of pages in the case where there is a source
folio. Therefore, split __wp_page_copy_user() into 2 variants:

__wp_page_copy_user_pfn() copies a single pfn to a destination page.
This is used when CoWing from a source without a folio, and is always
only a single page copy.

__wp_page_copy_user_range() copies a range of pages from source to
destination and is used when the source has an underlying folio. For now
it is only used to copy a single page, but this will change in a future
commit.

In both cases, kmsan_copy_page_meta() is moved into these helper
functions so that the caller does not need to be concerned with calling
it multiple times for the range case.

No functional changes intended.

Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
---
 mm/memory.c | 41 +++++++++++++++++++++++++++++------------
 1 file changed, 29 insertions(+), 12 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index 7e2af54fe2e0..f2b7cfb2efc0 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2786,14 +2786,34 @@ static inline int pte_unmap_same(struct vm_fault *vmf)
 	return same;
 }

+/*
+ * Return:
+ *	0:		copied succeeded
+ *	-EHWPOISON:	copy failed due to hwpoison in source page
+ */
+static inline int __wp_page_copy_user_range(struct page *dst, struct page *src,
+						int nr, unsigned long addr,
+						struct vm_area_struct *vma)
+{
+	for (; nr != 0; nr--, dst++, src++, addr += PAGE_SIZE) {
+		if (copy_mc_user_highpage(dst, src, addr, vma)) {
+			memory_failure_queue(page_to_pfn(src), 0);
+			return -EHWPOISON;
+		}
+		kmsan_copy_page_meta(dst, src);
+	}
+
+	return 0;
+}
+
 /*
  * Return:
  *	0:		copied succeeded
  *	-EHWPOISON:	copy failed due to hwpoison in source page
  *	-EAGAIN:	copied failed (some other reason)
  */
-static inline int __wp_page_copy_user(struct page *dst, struct page *src,
-				      struct vm_fault *vmf)
+static inline int __wp_page_copy_user_pfn(struct page *dst,
+						struct vm_fault *vmf)
 {
 	int ret;
 	void *kaddr;
@@ -2803,14 +2823,6 @@ static inline int __wp_page_copy_user(struct page *dst, struct page *src,
 	struct mm_struct *mm = vma->vm_mm;
 	unsigned long addr = vmf->address;

-	if (likely(src)) {
-		if (copy_mc_user_highpage(dst, src, addr, vma)) {
-			memory_failure_queue(page_to_pfn(src), 0);
-			return -EHWPOISON;
-		}
-		return 0;
-	}
-
 	/*
 	 * If the source page was a PFN mapping, we don't have
 	 * a "struct page" for it. We do a best-effort copy by
@@ -2879,6 +2891,7 @@ static inline int __wp_page_copy_user(struct page *dst, struct page *src,
 		}
 	}

+	kmsan_copy_page_meta(dst, NULL);
 	ret = 0;

 pte_unlock:
@@ -3372,7 +3385,12 @@ static vm_fault_t wp_page_copy(struct vm_fault *vmf)
 		if (!new_folio)
 			goto oom;

-		ret = __wp_page_copy_user(&new_folio->page, vmf->page, vmf);
+		if (likely(old_folio))
+			ret = __wp_page_copy_user_range(&new_folio->page,
+							vmf->page,
+							1, vmf->address, vma);
+		else
+			ret = __wp_page_copy_user_pfn(&new_folio->page, vmf);
 		if (ret) {
 			/*
 			 * COW failed, if the fault was solved by other,
@@ -3388,7 +3406,6 @@ static vm_fault_t wp_page_copy(struct vm_fault *vmf)
 			delayacct_wpcopy_end();
 			return ret == -EHWPOISON ? VM_FAULT_HWPOISON : 0;
 		}
-		kmsan_copy_page_meta(&new_folio->page, vmf->page);
 	}

 	if (mem_cgroup_charge(new_folio, mm, GFP_KERNEL))
--
2.25.1