Re: [PATCH 07/12] mm: Remove redundant pXd_devmap calls
From: David Hildenbrand <hidden>
Date: 2025-06-02 09:33:13
Also in:
dri-devel, linux-arm-kernel, linux-cxl, linux-ext4, linux-fsdevel, linux-mm, linux-riscv, linux-xfs, lkml, loongarch, nvdimm
quoted hunk ↗ jump to hunk
--- 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