[PATCH v3 0/2] mm/memory: improve insert_pages() error handling

[PATCH v3 0/2] mm/memory: improve insert_pages() error handling

[Avi Weiss]

Improve insert_pages() error handling.

The first patch simplifies error handling by initializing the error
status to zero and assigning error codes at their respective failure
sites.

The second patch returns -ENOMEM when walk_to_pmd() fails. A NULL
return from walk_to_pmd() indicates failure to allocate an upper
page-table level, so -ENOMEM is more appropriate than -EFAULT and is
consistent with the subsequent pte_alloc() failure.

Changes in v3:

* drop the walk_to_pmd() rename following review
* use the mm/memory: prefix consistently across the series
* carry review tags from v2
* rebase onto current mm-new

Link: https://lore.kernel.org/r/cover.1785847364.git.thnkslprpt@gmail.com/

Avi Weiss (2):
  mm/memory: simplify error handling in insert_pages()
  mm/memory: return -ENOMEM for page-table allocation failure in
    insert_pages()

 mm/memory.c | 22 +++++++++++-----------
 1 file changed, 11 insertions(+), 11 deletions(-)


base-commit: d2aad7fdcda7ae8a726926f2d6de7fe9e8ee7563
-- 
2.43.0

[PATCH v3 1/2] mm/memory: simplify error handling in insert_pages()

[Avi Weiss]

Initialize error return status to zero and then set it as needed at each
point of failure.

Assign -ENOMEM explicitly when pte_alloc() fails as the pte_alloc()
macro returns a boolean.

Signed-off-by: Avi Weiss <thnkslprpt@gmail.com>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
---
 mm/memory.c | 22 +++++++++++-----------
 1 file changed, 11 insertions(+), 11 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index 9cbce5c90bff..2561dc6bdde6 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2565,20 +2565,22 @@ static int insert_pages(struct vm_area_struct *vma, unsigned long addr,
 	unsigned long curr_page_idx = 0;
 	unsigned long remaining_pages_total = *num;
 	unsigned long pages_to_write_in_pmd;
-	int ret;
+	int err = 0;
 more:
-	ret = -EFAULT;
 	pmd = walk_to_pmd(mm, addr);
-	if (!pmd)
+	if (!pmd) {
+		err = -EFAULT;
 		goto out;
+	}
 
 	pages_to_write_in_pmd = min_t(unsigned long,
 		remaining_pages_total, PTRS_PER_PTE - pte_index(addr));
 
 	/* Allocate the PTE if necessary; takes PMD lock once only. */
-	ret = -ENOMEM;
-	if (pte_alloc(mm, pmd))
+	if (pte_alloc(mm, pmd)) {
+		err = -ENOMEM;
 		goto out;
+	}
 
 	while (pages_to_write_in_pmd) {
 		int pte_idx = 0;
@@ -2586,15 +2588,14 @@ static int insert_pages(struct vm_area_struct *vma, unsigned long addr,
 
 		start_pte = pte_offset_map_lock(mm, pmd, addr, &pte_lock);
 		if (!start_pte) {
-			ret = -EFAULT;
+			err = -EFAULT;
 			goto out;
 		}
 		for (pte = start_pte; pte_idx < batch_size; ++pte, ++pte_idx) {
-			int err = insert_page_in_batch_locked(vma, pte,
-				addr, pages[curr_page_idx], prot);
+			err = insert_page_in_batch_locked(vma, pte, addr,
+							  pages[curr_page_idx], prot);
 			if (unlikely(err)) {
 				pte_unmap_unlock(start_pte, pte_lock);
-				ret = err;
 				remaining_pages_total -= pte_idx;
 				goto out;
 			}
@@ -2607,10 +2608,9 @@ static int insert_pages(struct vm_area_struct *vma, unsigned long addr,
 	}
 	if (remaining_pages_total)
 		goto more;
-	ret = 0;
 out:
 	*num = remaining_pages_total;
-	return ret;
+	return err;
 }
 
 /**
-- 
2.43.0

[PATCH v3 2/2] mm/memory: return -ENOMEM for page-table allocation failure in insert_pages()

[Avi Weiss]

walk_to_pmd() returns NULL only when p4d_alloc(), pud_alloc(), or
pmd_alloc() fails. These are page-table allocation failures, but
insert_pages() currently reports them as -EFAULT.

Return -ENOMEM instead, consistent with the subsequent pte_alloc()
failure and with the single-page insert_page() path, which reports
failure of the same page-table allocation chain as -ENOMEM.

Address and range validation failures in vm_insert_pages() continue to
return -EFAULT. Keep the later -EFAULT return for
pte_offset_map_lock(), which is not an allocation failure.

Signed-off-by: Avi Weiss <thnkslprpt@gmail.com>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Reviewed-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
 mm/memory.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/memory.c b/mm/memory.c
index 2561dc6bdde6..27ffe1a99a08 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2569,7 +2569,7 @@ static int insert_pages(struct vm_area_struct *vma, unsigned long addr,
 more:
 	pmd = walk_to_pmd(mm, addr);
 	if (!pmd) {
-		err = -EFAULT;
+		err = -ENOMEM;
 		goto out;
 	}
 
-- 
2.43.0