Fuad Tabba <tabba@xxxxxxxxxx> writes:
> <snip>
>
> +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;
> + }
> + 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;
> + }
> +
> + /*
> + * Only private folios are marked as "guestmem" so far, and we never
> + * expect private folios at this point.
> + */
I think this is not quite accurate.
Based on my understanding and kvm_gmem_handle_folio_put() in this other
patch [1], only pages *in transition* from shared to private state are
marked "guestmem", although it is true that no private folios or folios
marked guestmem are expected here.
> + if (WARN_ON_ONCE(folio_test_guestmem(folio))) {
> + ret = VM_FAULT_SIGBUS;
> + goto out_folio;
> + }
> +
> + /* No support for huge pages. */
> + if (WARN_ON_ONCE(folio_test_large(folio))) {
> + ret = VM_FAULT_SIGBUS;
> + goto out_folio;
> + }
> +
> + if (!folio_test_uptodate(folio)) {
> + clear_highpage(folio_page(folio, 0));
> + kvm_gmem_mark_prepared(folio);
> + }
> +
> + vmf->page = folio_file_page(folio, vmf->pgoff);
> +
> +out_folio:
> + if (ret != VM_FAULT_LOCKED) {
> + folio_unlock(folio);
> + folio_put(folio);
> + }
> +
> +out_filemap:
> + filemap_invalidate_unlock_shared(inode->i_mapping);
> +
> + return ret;
> +}
>
> <snip>
[1] https://lore.kernel.org/all/20250117163001.2326672-7-tabba@xxxxxxxxxx/
