netdev - Re: [PATCH v2 6/8] vhost/vsock: Allocate nonlinear SKBs for handling large receive buffers

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Message-ID: <aHQnC-K4jn73I0Yb@willie-the-truck>
Date: Sun, 13 Jul 2025 22:37:15 +0100
From: Will Deacon <will@...nel.org>
To: Stefano Garzarella <sgarzare@...hat.com>
Cc: linux-kernel@...r.kernel.org, Keir Fraser <keirf@...gle.com>,
	Steven Moreland <smoreland@...gle.com>,
	Frederick Mayle <fmayle@...gle.com>,
	Stefan Hajnoczi <stefanha@...hat.com>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Jason Wang <jasowang@...hat.com>,
	Eugenio Pérez <eperezma@...hat.com>,
	netdev@...r.kernel.org, virtualization@...ts.linux.dev
Subject: Re: [PATCH v2 6/8] vhost/vsock: Allocate nonlinear SKBs for handling
 large receive buffers

On Wed, Jul 02, 2025 at 06:50:59PM +0200, Stefano Garzarella wrote:
> On Tue, Jul 01, 2025 at 05:45:05PM +0100, Will Deacon wrote:
> > -static inline struct sk_buff *virtio_vsock_alloc_skb(unsigned int size, gfp_t mask)
> > +static inline struct sk_buff *
> > +__virtio_vsock_alloc_skb_with_frags(unsigned int header_len,
> > +				    unsigned int data_len,
> > +				    gfp_t mask)
> > {
> > 	struct sk_buff *skb;
> > +	int err;
> > 
> > -	if (size < VIRTIO_VSOCK_SKB_HEADROOM)
> > -		return NULL;
> 
> I would have made this change in a separate patch, but IIUC the only other
> caller is virtio_transport_alloc_skb() where this condition is implied,
> right?

At this point in the series, virtio_vsock_alloc_skb() only has a single
caller (vhost_vsock_alloc_skb()) which already has a partial bounds check
and so this patch extends it to cover the lower bound.

Later (in "vsock/virtio: Allocate nonlinear SKBs for handling large
transmit buffers"), virtio_transport_alloc_skb() gets converted over
and that's fine because it never allocates less than
VIRTIO_VSOCK_SKB_HEADROOM.

> I don't know, maybe we could have one patch where you touch this and
> virtio_vsock_skb_rx_put(), and another where you introduce nonlinear
> allocation for vhost/vsock.  What do you think? (not a strong opinion, just
> worried about doing 2 things in a single patch)

I can spin a separate patch for the bounds check.

Will