On 17.05.24 17:07, Vincent Donnefort wrote:
Hi David,
[...]
-static int validate_page_before_insert(struct page *page)
+static bool vm_mixed_zeropage_allowed(struct vm_area_struct *vma)
+{
+ VM_WARN_ON_ONCE(vma->vm_flags & VM_PFNMAP);
+ /*
+ * Whoever wants to forbid the zeropage after some zeropages
+ * might already have been mapped has to scan the page tables and
+ * bail out on any zeropages. Zeropages in COW mappings can
+ * be unshared using FAULT_FLAG_UNSHARE faults.
+ */
+ if (mm_forbids_zeropage(vma->vm_mm))
+ return false;
+ /* zeropages in COW mappings are common and unproblematic. */
+ if (is_cow_mapping(vma->vm_flags))
+ return true;
+ /* Mappings that do not allow for writable PTEs are unproblematic. */
+ if (!(vma->vm_flags & (VM_WRITE | VM_MAYWRITE)))
+ return false;
Shouldn't we return true here?
Indeed, thanks! I wish we would have user in the tree already that could
exercise that code path.
[...]
@@ -2043,7 +2085,7 @@ static int insert_page_in_batch_locked(struct vm_area_struct *vma, pte_t *pte,
if (!page_count(page))
return -EINVAL;
This test here prevents inserting the zero-page.
You mean the existing page_count() check? or the (wrong) vma->vm_flags
check in vm_mixed_zeropage_allowed() ?
--
Cheers,
David / dhildenb
