netdev - Re: [RFC PATCH v3 01/11] virtio/vsock: rework packet allocation logic

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Date:   Sun, 6 Nov 2022 20:50:42 +0100
From:   Christophe JAILLET <christophe.jaillet@...adoo.fr>
To:     Arseniy Krasnov <AVKrasnov@...rdevices.ru>,
        Stefano Garzarella <sgarzare@...hat.com>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Krasnov Arseniy <oxffffaa@...il.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        kernel <kernel@...rdevices.ru>
Subject: Re: [RFC PATCH v3 01/11] virtio/vsock: rework packet allocation logic

Le 06/11/2022 à 20:36, Arseniy Krasnov a écrit :
> 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@...rdevices.ru>
> ---
>   drivers/vhost/vsock.c                   |  1 +
>   include/linux/virtio_vsock.h            |  1 +
>   net/vmw_vsock/virtio_transport.c        |  8 ++++++--
>   net/vmw_vsock/virtio_transport_common.c | 10 +++++++++-
>   4 files changed, 17 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
> index 5703775af129..65475d128a1d 100644
> --- a/drivers/vhost/vsock.c
> +++ b/drivers/vhost/vsock.c
> @@ -399,6 +399,7 @@ vhost_vsock_alloc_pkt(struct vhost_virtqueue *vq,
>   		return NULL;
>   	}
>   
> +	pkt->slab_buf = true;
>   	pkt->buf_len = pkt->len;
>   
>   	nbytes = copy_from_iter(pkt->buf, pkt->len, &iov_iter);
> 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 a9980e9b9304..37e8dbfe2f5d 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);
> @@ -1339,7 +1340,14 @@ EXPORT_SYMBOL_GPL(virtio_transport_recv_pkt);
>   
>   void virtio_transport_free_pkt(struct virtio_vsock_pkt *pkt)
>   {
> -	kvfree(pkt->buf);
> +	if (pkt->buf_len) {
> +		if (pkt->slab_buf)
> +			kvfree(pkt->buf);

Hi,

kfree()? (according to virtio_transport_alloc_pkt() in -next) or 
something else need to be changed.

> +		else
> +			free_pages((unsigned long)pkt->buf,
> +				   get_order(pkt->buf_len));

In virtio_vsock_rx_fill(), only alloc_page() is used.

Should this be alloc_pages(.., get_order(buf_len)) or free_page() 
(without an 's') here?

Just my 2c,

CJ

> +	}
> +
>   	kfree(pkt);
>   }
>   EXPORT_SYMBOL_GPL(virtio_transport_free_pkt);