Re: [PATCH v5 3/9] KVM: guest_memfd: Allow host to map guest_memfd() pages

[James Houghton <jthoughton@xxxxxxxxxx>]

On Mon, Mar 3, 2025 at 9:10 AM Fuad Tabba <tabba@xxxxxxxxxx> wrote:
> +static vm_fault_t kvm_gmem_fault(struct vm_fault *vmf)
> +{
> +       struct inode *inode = file_inode(vmf->vma->vm_file);
> +       struct folio *folio;
> +       vm_fault_t ret = VM_FAULT_LOCKED;
> +
> +       filemap_invalidate_lock_shared(inode->i_mapping);
> +
> +       folio = kvm_gmem_get_folio(inode, vmf->pgoff);
> +       if (IS_ERR(folio)) {
> +               switch (PTR_ERR(folio)) {
> +               case -EAGAIN:
> +                       ret = VM_FAULT_RETRY;
> +                       break;
> +               case -ENOMEM:
> +                       ret = VM_FAULT_OOM;
> +                       break;
> +               default:
> +                       ret = VM_FAULT_SIGBUS;
> +                       break;

Tiny nit-pick: This smells almost like an open-coded vmf_error(). For
the non-EAGAIN case, can we just call vmf_error()?

> +               }
> +               goto out_filemap;
> +       }
> +
> +       if (folio_test_hwpoison(folio)) {
> +               ret = VM_FAULT_HWPOISON;
> +               goto out_folio;
> +       }
> +
> +       /* Must be called with folio lock held, i.e., after kvm_gmem_get_folio() */
> +       if (!kvm_gmem_offset_is_shared(vmf->vma->vm_file, vmf->pgoff)) {
> +               ret = VM_FAULT_SIGBUS;
> +               goto out_folio;
> +       }