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

[Christophe JAILLET]

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@xxxxxxxxxxxxxx>
> > > ---
> > >    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);