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Date: Mon, 7 Nov 2022 22:24:05 +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 07/11/2022 à 06:23, Arseniy Krasnov a écrit :
> On 06.11.2022 22:50, Christophe JAILLET wrote:
>> 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.
>>
> Hello Cristophe,
>
> I think, 'kvfree()' is still needed here, because buffer for packet could be allocated by 'kvmalloc()'
> in drivers/vhost/vsock.c. Correct me if i'm wrong.
Agreed.
>
>>> + 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?
> This function frees packets which were allocated in vhost path also. In vhost, for zerocopy
> packets alloc_pageS() is used.
Ok. Seen in patch 5/11.
But wouldn't it be cleaner and future-proof to also have alloc_pageS()
in virtio_vsock_rx_fill(), even if get_order(buf->len) is kwown to be 0?
What, if for some reason a PAGE_SIZE was < 4kb for a given arch, or
VIRTIO_VSOCK_DEFAULT_RX_BUF_SIZE increased?
CJ
>
> Thank You, Arseniy
>>
>> Just my 2c,
>>
>> CJ
>>
>>> + }
>>> +
>>> kfree(pkt);
>>> }
>>> EXPORT_SYMBOL_GPL(virtio_transport_free_pkt);
>>
>
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