diff mbox series

[5.10,110/152] mm: dont play games with pinned pages in clear_page_refs

Message ID 20210118113358.001978134@linuxfoundation.org
State New
Headers show
Series None | expand

Commit Message

Greg Kroah-Hartman Jan. 18, 2021, 11:34 a.m. UTC 
From: Linus Torvalds <torvalds@linux-foundation.org>

[ Upstream commit 9348b73c2e1bfea74ccd4a44fb4ccc7276ab9623 ]

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 <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/proc/task_mmu.c | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)
diff mbox series

Patch

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index ab7d700b2caa4..602e3a52884d8 100644
--- 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);