+static void damon_va_mkold(struct mm_struct *mm, unsigned long addr)
+{
+	pte_t *pte = NULL;
+	pmd_t *pmd = NULL;
+	spinlock_t *ptl;
+

I just stumbled over this, sorry for the dumb questions:


a) What do we know about that region we are messing with?

AFAIU, just like follow_pte() and follow_pfn(), follow_invalidate_pte() 
should only be called on VM_IO and raw VM_PFNMAP mappings in general 
(see the doc of follow_pte()). Do you even know that it's within a 
single VMA and that there are no concurrent modifications?

b) Which locks are we holding?

I hope we're holding the mmap lock in read mode at least. Or how are you 
making sure there are no concurrent modifications to page tables / VMA 
layout ... ?

+	if (follow_invalidate_pte(mm, addr, NULL, &pte, &pmd, &ptl))

-- 
Thanks,

David / dhildenb