On Mon, Mar 02, 2026 at 11:07:41AM +0100, Christian König wrote:
> As far as I know background is that on x86 pte_special() only works
> on true leave pte but not pmd/pud.
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
