mm: don't play games with pinned pages in clear_page_refs

Turning a pinned page read-only breaks the pinning after COW. Don't do it. The whole "track page soft dirty" state doesn't work with pinned pages anyway, since the page might be dirtied by the pinning entity without ever being noticed in the page tables. Signed-off-by: Linus Torvalds <[email protected]>
ashr · Jan 16, 2021 · 9348b73 · 9348b73
1 parent 29a951d
commit 9348b73
Showing 1 changed file with 21 additions and 0 deletions.
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
@@ -1035,6 +1035,25 @@ struct clear_refs_private {
 };
 
 #ifdef CONFIG_MEM_SOFT_DIRTY
+
+#define is_cow_mapping(flags) (((flags) & (VM_SHARED | VM_MAYWRITE)) == VM_MAYWRITE)
+
+static inline bool pte_is_pinned(struct vm_area_struct *vma, unsigned long addr, pte_t pte)
+{
+	struct page *page;
+
+	if (!pte_write(pte))
+		return false;
+	if (!is_cow_mapping(vma->vm_flags))
+		return false;
+	if (likely(!atomic_read(&vma->vm_mm->has_pinned)))
+		return false;
+	page = vm_normal_page(vma, addr, pte);
+	if (!page)
+		return false;
+	return page_maybe_dma_pinned(page);
+}
+
 static inline void clear_soft_dirty(struct vm_area_struct *vma,
 		unsigned long addr, pte_t *pte)
 {
@@ -1049,6 +1068,8 @@ static inline void clear_soft_dirty(struct vm_area_struct *vma,
 	if (pte_present(ptent)) {
 		pte_t old_pte;
 
+		if (pte_is_pinned(vma, addr, ptent))
+			return;
 		old_pte = ptep_modify_prot_start(vma, addr, pte);
 		ptent = pte_wrprotect(old_pte);
 		ptent = pte_clear_soft_dirty(ptent);