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    SubjectRE: [RFC PATCH v11 12/29] KVM: Add KVM_CREATE_GUEST_MEMFD ioctl() for guest-specific backing memory
    Date
    On Wednesday, July 19, 2023 7:45 AM, Sean Christopherson wrote:
    > +int kvm_gmem_get_pfn(struct kvm *kvm, struct kvm_memory_slot *slot,
    > + gfn_t gfn, kvm_pfn_t *pfn, int *max_order) {
    > + pgoff_t index = gfn - slot->base_gfn + slot->gmem.pgoff;
    > + struct kvm_gmem *gmem;
    > + struct folio *folio;
    > + struct page *page;
    > + struct file *file;
    > +
    > + file = kvm_gmem_get_file(slot);
    > + if (!file)
    > + return -EFAULT;
    > +
    > + gmem = file->private_data;
    > +
    > + if (WARN_ON_ONCE(xa_load(&gmem->bindings, index) != slot)) {
    > + fput(file);
    > + return -EIO;
    > + }
    > +
    > + folio = kvm_gmem_get_folio(file_inode(file), index);
    > + if (!folio) {
    > + fput(file);
    > + return -ENOMEM;
    > + }
    > +
    > + page = folio_file_page(folio, index);
    > +
    > + *pfn = page_to_pfn(page);
    > + *max_order = compound_order(compound_head(page));

    Maybe better to check if caller provided a buffer to get the max_order:
    if (max_order)
    *max_order = compound_order(compound_head(page));

    This is what the previous version did (restrictedmem_get_page),
    so that callers who only want to get a pfn don't need to define
    an unused "order" param.
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