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This is not the case, there are pmd and pud_special as well, protected by CONFIG_xx The arch should not define CONFIG_ARCH_SUPPORTS_PMD_PFNMAP if vmf_insert_pfn_pmd() doesn't result in pmd_special() working, for example. eg: vmf_insert_pfn_pmd() insert_pmd() if (fop.is_folio) { // Not Taken } else { entry = pmd_mkhuge(pfn_pmd(fop.pfn, prot)); entry = pmd_mkspecial(entry); This stuff was all put together by Peter specifically for VFIO to use, AFAIK it is correct. IDK what Thomas was using, but if you tried to do huge faults before all of this was built it definitely would not work right as it only supported a folio backed path. Jason