Re: [PATCH v6 16/26] huge_memory: Add vmf_insert_folio_pmd()

David Hildenbrand
2025-01-14T16:42:19Z

> +vm_fault_t vmf_insert_folio_pmd(struct vm_fault *vmf, struct folio *folio, bool write)
> +{
> + struct vm_area_struct *vma = vmf->vma;
> + unsigned long addr = vmf->address & PMD_MASK;
> + struct mm_struct *mm = vma->vm_mm;
> + spinlock_t *ptl;
> + pgtable_t pgtable = NULL;
> +
> + if (addr < vma->vm_start || addr >= vma->vm_end)
> + return VM_FAULT_SIGBUS;
> +
> + if (WARN_ON_ONCE(folio_order(folio) != PMD_ORDER))
> + return VM_FAULT_SIGBUS;
> +
> + if (arch_needs_pgtable_deposit()) {
> + pgtable = pte_alloc_one(vma->vm_mm);
> + if (!pgtable)
> + return VM_FAULT_OOM;
> + }

This is interesting and nasty at the same time (only to make ppc64 boo3s
with has tables happy). But it seems to be the right thing to do.

> +
> + ptl = pmd_lock(mm, vmf->pmd);
> + if (pmd_none(*vmf->pmd)) {
> + folio_get(folio);
> + folio_add_file_rmap_pmd(folio, &folio->page, vma);
> + add_mm_counter(mm, mm_counter_file(folio), HPAGE_PMD_NR);
> + }
> + insert_pfn_pmd(vma, addr, vmf->pmd, pfn_to_pfn_t(folio_pfn(folio)),
> + vma->vm_page_prot, write, pgtable);
> + spin_unlock(ptl);
> + if (pgtable)
> + pte_free(mm, pgtable);

Ehm, are you unconditionally freeing the pgtable, even if consumed by
insert_pfn_pmd() ?

Note that setting pgtable to NULL in insert_pfn_pmd() when consumed will
not be visible here.

You'd have to pass a pointer to the ... pointer (&pgtable).

... unless I am missing something, staring at the diff.

--
Cheers,

David / dhildenb