On Fri, 2022-10-14 at 17:32 +0200, Peter Zijlstra wrote:

On Thu, Sep 29, 2022 at 03:29:13PM -0700, Rick Edgecombe wrote:

quoted

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 8cd413c5a329..fef14ab3abcb 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h

@@ -981,13 +981,25 @@ void free_compound_page(struct page *page);
   * servicing faults for write access.  In the normal case, do

always want
   * pte_mkwrite.  But get_user_pages can cause write faults for
mappings
   * that do not have writing enabled, when used by
access_process_vm.
+ *
+ * If a vma is shadow stack (a type of writable memory), mark the
pte shadow
+ * stack.
   */
+#ifndef maybe_mkwrite
  static inline pte_t maybe_mkwrite(pte_t pte, struct
vm_area_struct *vma)
  {
-     if (likely(vma->vm_flags & VM_WRITE))
+     if (!(vma->vm_flags & VM_WRITE))
+             goto out;
+
+     if (vma->vm_flags & VM_SHADOW_STACK)
+             pte = pte_mkwrite_shstk(pte);
+     else
               pte = pte_mkwrite(pte);
+
+out:
       return pte;
  }
+#endif

Why the #ifndef guard? There is no other implementation, nor does
this
patch introduce one.

Oh yea, this series used to add another one, but I forgot to remove the
guards. Thanks.

Also, wouldn't it be simpler to write it like:

static inline pte_t maybe_mkwrite(pte_t pte, struct vm_area_struct
*vma)
{
        if (!(vma->vm_flags & VM_WRITE))
                return pte;

        if (vma->vm_flags & VM_SHADOW_STACK)
                return pte_mkwrite_shstk(pte);

        return pte_mkwrite(pte);
}

Yep, that looks better. Thanks.