On Tue, Oct 31, 2023, Chao Gao wrote:
> >+int kvm_gmem_create(struct kvm *kvm, struct kvm_create_guest_memfd *args)
> >+{
> >+ loff_t size = args->size;
> >+ u64 flags = args->flags;
> >+ u64 valid_flags = 0;
> >+
> >+ if (flags & ~valid_flags)
> >+ return -EINVAL;
> >+
> >+ if (size < 0 || !PAGE_ALIGNED(size))
> >+ return -EINVAL;
>
> is size == 0 a valid case?
Nope, this is a bug.
> >+ if (!xa_empty(&gmem->bindings) &&
> >+ xa_find(&gmem->bindings, &start, end - 1, XA_PRESENT)) {
> >+ filemap_invalidate_unlock(inode->i_mapping);
> >+ goto err;
> >+ }
> >+
> >+ /*
> >+ * No synchronize_rcu() needed, any in-flight readers are guaranteed to
> >+ * be see either a NULL file or this new file, no need for them to go
> >+ * away.
> >+ */
> >+ rcu_assign_pointer(slot->gmem.file, file);
> >+ slot->gmem.pgoff = start;
> >+
> >+ xa_store_range(&gmem->bindings, start, end - 1, slot, GFP_KERNEL);
> >+ filemap_invalidate_unlock(inode->i_mapping);
> >+
> >+ /*
> >+ * Drop the reference to the file, even on success. The file pins KVM,
> >+ * not the other way 'round. Active bindings are invalidated if the
> >+ * file is closed before memslots are destroyed.
> >+ */
> >+ fput(file);
> >+ return 0;
> >+
> >+err:
> >+ fput(file);
> >+ return -EINVAL;
>
> The cleanup, i.e., filemap_invalidate_unlock() and fput(), is common. So, I
> think it
> may be slightly better to consolidate the common part e.g.,
I would prefer to keep this as-is. Only goto needs the unlock, and I find it
easier
to understand the success vs. error paths with explicit returns. But it's not a
super strong preference.
