Re: [RFC PATCH v2 1/8] virtio/vsock: rework packet allocation logic

[Stefano Garzarella]

On Fri, Jun 03, 2022 at 05:31:00AM +0000, Arseniy Krasnov wrote:
> To support zerocopy receive, packet's buffer allocation
> is changed: for buffers which could be mapped to user's
> vma we can't use 'kmalloc()'(as kernel restricts to map
> slab pages to user's vma) and raw buddy allocator now
> called. But, for tx packets(such packets won't be mapped
> to user), previous 'kmalloc()' way is used, but with special
> flag in packet's structure which allows to distinguish
> between 'kmalloc()' and raw pages buffers.
>
> Signed-off-by: Arseniy Krasnov <AVKrasnov@xxxxxxxxxxxxxx>
> ---
> include/linux/virtio_vsock.h            | 1 +
> net/vmw_vsock/virtio_transport.c        | 8 ++++++--
> net/vmw_vsock/virtio_transport_common.c | 9 ++++++++-
> 3 files changed, 15 insertions(+), 3 deletions(-)

Each patch should as much as possible work to not break the 
bisectability, and here we are not touching vhost_vsock_alloc_pkt() that 
uses kmalloc to allocate the buffer.

I see you updated it in the next patch, that should be fine, but here 
you should set slab_buf in vhost_vsock_alloc_pkt(), or you can merge the 
two patches.

> diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
> index 35d7eedb5e8e..d02cb7aa922f 100644
> --- a/include/linux/virtio_vsock.h
> +++ b/include/linux/virtio_vsock.h
> @@ -50,6 +50,7 @@ struct virtio_vsock_pkt {
> 	u32 off;
> 	bool reply;
> 	bool tap_delivered;
> +	bool slab_buf;
> };
>
> struct virtio_vsock_pkt_info {
> diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
> index ad64f403536a..19909c1e9ba3 100644
> --- a/net/vmw_vsock/virtio_transport.c
> +++ b/net/vmw_vsock/virtio_transport.c
> @@ -255,16 +255,20 @@ static void virtio_vsock_rx_fill(struct virtio_vsock *vsock)
> 	vq = vsock->vqs[VSOCK_VQ_RX];
>
> 	do {
> +		struct page *buf_page;
> +
> 		pkt = kzalloc(sizeof(*pkt), GFP_KERNEL);
> 		if (!pkt)
> 			break;
>
> -		pkt->buf = kmalloc(buf_len, GFP_KERNEL);
> -		if (!pkt->buf) {
> +		buf_page = alloc_page(GFP_KERNEL);
> +
> +		if (!buf_page) {
> 			virtio_transport_free_pkt(pkt);
> 			break;
> 		}
>
> +		pkt->buf = page_to_virt(buf_page);
> 		pkt->buf_len = buf_len;
> 		pkt->len = buf_len;
>
> diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
> index ec2c2afbf0d0..278567f748f2 100644
> --- a/net/vmw_vsock/virtio_transport_common.c
> +++ b/net/vmw_vsock/virtio_transport_common.c
> @@ -69,6 +69,7 @@ virtio_transport_alloc_pkt(struct virtio_vsock_pkt_info *info,
> 		if (!pkt->buf)
> 			goto out_pkt;
>
> +		pkt->slab_buf = true;
> 		pkt->buf_len = len;
>
> 		err = memcpy_from_msg(pkt->buf, info->msg, len);
> @@ -1342,7 +1343,13 @@ EXPORT_SYMBOL_GPL(virtio_transport_recv_pkt);
>
> void virtio_transport_free_pkt(struct virtio_vsock_pkt *pkt)
> {
> -	kfree(pkt->buf);
> +	if (pkt->buf_len) {
> +		if (pkt->slab_buf)
> +			kfree(pkt->buf);
> +		else
> +			free_pages(buf, get_order(pkt->buf_len));
> +	}
> +
> 	kfree(pkt);
> }
> EXPORT_SYMBOL_GPL(virtio_transport_free_pkt);
> --
> 2.25.1