Re: [RFC PATCH v11 12/29] KVM: Add KVM_CREATE_GUEST_MEMFD ioctl() for guest-specific backing memory

[Isaku Yamahata]

On Tue, Jul 18, 2023 at 04:44:55PM -0700,
Sean Christopherson <seanjc@xxxxxxxxxx> wrote:

> +static int kvm_gmem_release(struct inode *inode, struct file *file)
> +{
> +	struct kvm_gmem *gmem = file->private_data;
> +	struct kvm_memory_slot *slot;
> +	struct kvm *kvm = gmem->kvm;
> +	unsigned long index;
> +
> +	filemap_invalidate_lock(inode->i_mapping);
> +
> +	/*
> +	 * Prevent concurrent attempts to *unbind* a memslot.  This is the last
> +	 * reference to the file and thus no new bindings can be created, but
> +	 * dereferencing the slot for existing bindings needs to be protected
> +	 * against memslot updates, specifically so that unbind doesn't race
> +	 * and free the memslot (kvm_gmem_get_file() will return NULL).
> +	 */
> +	mutex_lock(&kvm->slots_lock);
> +
> +	xa_for_each(&gmem->bindings, index, slot)
> +		rcu_assign_pointer(slot->gmem.file, NULL);
> +
> +	synchronize_rcu();
> +
> +	/*
> +	 * All in-flight operations are gone and new bindings can be created.
> +	 * Zap all SPTEs pointed at by this file.  Do not free the backing
> +	 * memory, as its lifetime is associated with the inode, not the file.
> +	 */
> +	kvm_gmem_invalidate_begin(gmem, 0, -1ul);
> +	kvm_gmem_invalidate_end(gmem, 0, -1ul);
> +
> +	mutex_unlock(&kvm->slots_lock);
> +
> +	list_del(&gmem->entry);
> +
> +	filemap_invalidate_unlock(inode->i_mapping);
> +
> +	xa_destroy(&gmem->bindings);
> +	kfree(gmem);
> +
> +	kvm_put_kvm(kvm);
> +
> +	return 0;
> +}

The lockdep complains with the filemapping lock and the kvm slot lock.