linux-kernel - Re: [RFC PATCH 07/13] vsock: handle buffer

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Message-ID: <20191009123026.GH5747@stefanha-x1.localdomain>
Date:   Wed, 9 Oct 2019 13:30:26 +0100
From:   Stefan Hajnoczi <stefanha@...il.com>
To:     Stefano Garzarella <sgarzare@...hat.com>
Cc:     netdev@...r.kernel.org, Sasha Levin <sashal@...nel.org>,
        linux-hyperv@...r.kernel.org,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        kvm@...r.kernel.org, "Michael S. Tsirkin" <mst@...hat.com>,
        Dexuan Cui <decui@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        Stefan Hajnoczi <stefanha@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jorgen Hansen <jhansen@...are.com>
Subject: Re: [RFC PATCH 07/13] vsock: handle buffer_size sockopts in the core

On Fri, Sep 27, 2019 at 01:26:57PM +0200, Stefano Garzarella wrote:
> @@ -140,18 +145,11 @@ struct vsock_transport {
>  		struct vsock_transport_send_notify_data *);
>  	int (*notify_send_post_enqueue)(struct vsock_sock *, ssize_t,
>  		struct vsock_transport_send_notify_data *);
> +	int (*notify_buffer_size)(struct vsock_sock *, u64 *);

Is ->notify_buffer_size() called under lock_sock(sk)?  If yes, please
document it.

> +static void vsock_update_buffer_size(struct vsock_sock *vsk,
> +				     const struct vsock_transport *transport,
> +				     u64 val)
> +{
> +	if (val > vsk->buffer_max_size)
> +		val = vsk->buffer_max_size;
> +
> +	if (val < vsk->buffer_min_size)
> +		val = vsk->buffer_min_size;
> +
> +	if (val != vsk->buffer_size &&
> +	    transport && transport->notify_buffer_size)
> +		transport->notify_buffer_size(vsk, &val);

Why does this function return an int if we don't check the return value?

> diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
> index fc046c071178..bac9e7430a2e 100644
> --- a/net/vmw_vsock/virtio_transport_common.c
> +++ b/net/vmw_vsock/virtio_transport_common.c
> @@ -403,17 +403,13 @@ int virtio_transport_do_socket_init(struct vsock_sock *vsk,
>  	if (psk) {
>  		struct virtio_vsock_sock *ptrans = psk->trans;
>  
> -		vvs->buf_size	= ptrans->buf_size;
> -		vvs->buf_size_min = ptrans->buf_size_min;
> -		vvs->buf_size_max = ptrans->buf_size_max;
>  		vvs->peer_buf_alloc = ptrans->peer_buf_alloc;
> -	} else {
> -		vvs->buf_size = VIRTIO_VSOCK_DEFAULT_BUF_SIZE;
> -		vvs->buf_size_min = VIRTIO_VSOCK_DEFAULT_MIN_BUF_SIZE;
> -		vvs->buf_size_max = VIRTIO_VSOCK_DEFAULT_MAX_BUF_SIZE;
>  	}
>  
> -	vvs->buf_alloc = vvs->buf_size;
> +	if (vsk->buffer_size > VIRTIO_VSOCK_MAX_BUF_SIZE)
> +		vsk->buffer_size = VIRTIO_VSOCK_MAX_BUF_SIZE;

Hmm...this could be outside the [min, max] range.  I'm not sure how much
it matters.

Another issue is that this patch drops the VIRTIO_VSOCK_MAX_BUF_SIZE
limit that used to be enforced by virtio_transport_set_buffer_size().
Now the limit is only applied at socket init time.  If the buffer size
is changed later then VIRTIO_VSOCK_MAX_BUF_SIZE can be exceeded.  If
that doesn't matter, why even bother with VIRTIO_VSOCK_MAX_BUF_SIZE
here?


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