--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1398,10 +1398,7 @@ static int insert_pfn_pmd(struct vm_area_struct *vma, 
unsigned long addr,
        }
entry = pmd_mkhuge(pfn_t_pmd(pfn, prot));
-       if (pfn_t_devmap(pfn))
-               entry = pmd_mkdevmap(entry);
-       else
-               entry = pmd_mkspecial(entry);
+       entry = pmd_mkspecial(entry);
        if (write) {


I just stumbled over this, and I think there is something off here in the PMD/PUD case.

vmf_insert_folio_pmd() does a folio_get() + folio_add_file_rmap_pmd().

But then, we go ahead and turn this into a special mapping by setting it pmd_mkdevmap()/pmd_mkspecial().

Consequently, vm_normal_page_pmd() would ignore them, not following the rules documented for vm_normal_page() and behaving differently than vmf_insert_page_mkwrite()->insert_page().


folio_add_file_rmap_pmd() should never set these things special/devmap in the first place :/

What am I missing?

Note that fs/dax.c calls vmf_insert_folio_pmd() for PMDs and vmf_insert_page_mkwrite() for PTEs.

Consequently, PTEs will never be marked special (corner case, shared zeropage), but PMDs would always.

Hm?

--
Cheers,

David / dhildenb


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