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Why would pmd and pte be different? > > > I think for any p[mu]d where p[mu]d_page() is ok to use should never set > > 'special', right? > > There should be dedicated functions for installing pages and PFNs, > only the PFN one would set the special bit. > > And certainly your tests *should* be failing as special entries should > never ever be converted to struct page. That's the point, the pmd and pud special bit is not considered for gup. So fixing that requires making it not break dax, but looks like David has a cleanup for that.