[PATCH 1/4] mm: allow guard regions in file-backed and read-only mappings

[Lorenzo Stoakes]

There is no reason to disallow guard regions in file-backed mappings -
readahead and fault-around both function correctly in the presence of PTE
markers, equally other operations relating to memory-mapped files function
correctly.

Additionally, read-only mappings if introducing guard-regions, only
restrict the mapping further, which means there is no violation of any
access rights by permitting this to be so.

Removing this restriction allows for read-only mapped files (such as
executable files) correctly which would otherwise not be permitted.

Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
---
 mm/madvise.c | 8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)

diff --git a/mm/madvise.c b/mm/madvise.c
index 6ecead476a80..e01e93e179a8 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -1051,13 +1051,7 @@ static bool is_valid_guard_vma(struct vm_area_struct *vma, bool allow_locked)
 	if (!allow_locked)
 		disallowed |= VM_LOCKED;
 
-	if (!vma_is_anonymous(vma))
-		return false;
-
-	if ((vma->vm_flags & (VM_MAYWRITE | disallowed)) != VM_MAYWRITE)
-		return false;
-
-	return true;
+	return !(vma->vm_flags & disallowed);
 }
 
 static bool is_guard_pte_marker(pte_t ptent)
-- 
2.48.1