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

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Date:   Thu, 9 Jun 2022 10:37:45 +0200
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     Arseniy Krasnov <AVKrasnov@...rdevices.ru>
Cc:     Stefan Hajnoczi <stefanha@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jason Wang <jasowang@...hat.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        "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>,
        Krasnov Arseniy <oxffffaa@...il.com>
Subject: Re: [RFC PATCH v2 1/8] virtio/vsock: rework packet allocation logic

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@...rdevices.ru>
>---
> 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