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

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Date:   Mon, 7 Nov 2022 05:23:47 +0000
From:   Arseniy Krasnov <AVKrasnov@...rdevices.ru>
To:     Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        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

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.

>> +        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.

Thank You, Arseniy
> 
> Just my 2c,
> 
> CJ
> 
>> +    }
>> +
>>       kfree(pkt);
>>   }
>>   EXPORT_SYMBOL_GPL(virtio_transport_free_pkt);
>