On Mon, 9 Sep 2024 16:38:16 +0800, Jason Wang <jasowang@xxxxxxxxxx> wrote:
> On Fri, Sep 6, 2024 at 5:32 PM Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx> wrote:
> >
> > On Fri, 6 Sep 2024 05:08:56 -0400, "Michael S. Tsirkin" <mst@xxxxxxxxxx> wrote:
> > > On Fri, Sep 06, 2024 at 04:53:38PM +0800, Xuan Zhuo wrote:
> > > > On Fri, 6 Sep 2024 04:43:29 -0400, "Michael S. Tsirkin" <mst@xxxxxxxxxx> wrote:
> > > > > On Tue, Aug 20, 2024 at 03:19:13PM +0800, Xuan Zhuo wrote:
> > > > > > leads to regression on VM with the sysctl value of:
> > > > > >
> > > > > > - net.core.high_order_alloc_disable=1
> > > > > >
> > > > > > which could see reliable crashes or scp failure (scp a file 100M in size
> > > > > > to VM):
> > > > > >
> > > > > > The issue is that the virtnet_rq_dma takes up 16 bytes at the beginning
> > > > > > of a new frag. When the frag size is larger than PAGE_SIZE,
> > > > > > everything is fine. However, if the frag is only one page and the
> > > > > > total size of the buffer and virtnet_rq_dma is larger than one page, an
> > > > > > overflow may occur. In this case, if an overflow is possible, I adjust
> > > > > > the buffer size. If net.core.high_order_alloc_disable=1, the maximum
> > > > > > buffer size is 4096 - 16. If net.core.high_order_alloc_disable=0, only
> > > > > > the first buffer of the frag is affected.
> > > > > >
> > > > > > Fixes: f9dac92ba908 ("virtio_ring: enable premapped mode whatever use_dma_api")
> > > > > > Reported-by: "Si-Wei Liu" <si-wei.liu@xxxxxxxxxx>
> > > > > > Closes: http://lore.kernel.org/all/8b20cc28-45a9-4643-8e87-ba164a540c0a@xxxxxxxxxx
> > > > > > Signed-off-by: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
> > > > >
> > > > >
> > > > > Guys where are we going with this? We have a crasher right now,
> > > > > if this is not fixed ASAP I'd have to revert a ton of
> > > > > work Xuan Zhuo just did.
> > > >
> > > > I think this patch can fix it and I tested it.
> > > > But Darren said this patch did not work.
> > > > I need more info about the crash that Darren encountered.
> > > >
> > > > Thanks.
> > >
> > > So what are we doing? Revert the whole pile for now?
> > > Seems to be a bit of a pity, but maybe that's the best we can do
> > > for this release.
> >
> > @Jason Could you review this?
>
> I think we probably need some tweaks for this patch.
>
> For example, the changelog is not easy to be understood especially
> consider it starts something like:
>
> "
> leads to regression on VM with the sysctl value of:
>
> - net.core.high_order_alloc_disable=1
>
> which could see reliable crashes or scp failure (scp a file 100M in size
> to VM):
> "
>
> Need some context and actually sysctl is not a must to reproduce the
> issue, it can also happen when memory is fragmented.
OK.
>
> Another issue is that, if we move the skb_page_frag_refill() out of
> the virtnet_rq_alloc(). The function semantics turns out to be weird:
>
> skb_page_frag_refill(len, &rq->alloc_frag, gfp);
> ...
> virtnet_rq_alloc(rq, len, gfp);
YES.
>
> I wonder instead of subtracting the dma->len, how about simply count
> the dma->len in len if we call virtnet_rq_aloc() in
> add_recvbuf_small()?
1. For the small mode, it is safe. That just happens in the merge mode.
2. In the merge mode, if we count the dma->len in len, we should know
if the frag->offset is zero or not. We can not do that before
skb_page_frag_refill(), because skb_page_frag_refill() may allocate
new page, the frag->offset is zero. So the judgment must is after
skb_page_frag_refill().
Thanks.
>
> >
> > I think this problem is clear, though I do not know why it did not work
> > for Darren.
>
> I had a try. This issue could be reproduced easily and this patch
> seems to fix the issue with a KASAN enabled kernel.
>
> Thanks
>
> >
> > Thanks.
> >
> >
> > >
> > >
> > > > >
> > > > >
> > > > > > ---
> > > > > > drivers/net/virtio_net.c | 12 +++++++++---
> > > > > > 1 file changed, 9 insertions(+), 3 deletions(-)
> > > > > >
> > > > > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > > > > > index c6af18948092..e5286a6da863 100644
> > > > > > --- a/drivers/net/virtio_net.c
> > > > > > +++ b/drivers/net/virtio_net.c
> > > > > > @@ -918,9 +918,6 @@ static void *virtnet_rq_alloc(struct receive_queue *rq, u32 size, gfp_t gfp)
> > > > > > void *buf, *head;
> > > > > > dma_addr_t addr;
> > > > > >
> > > > > > - if (unlikely(!skb_page_frag_refill(size, alloc_frag, gfp)))
> > > > > > - return NULL;
> > > > > > -
> > > > > > head = page_address(alloc_frag->page);
> > > > > >
> > > > > > dma = head;
> > > > > > @@ -2421,6 +2418,9 @@ static int add_recvbuf_small(struct virtnet_info *vi, struct receive_queue *rq,
> > > > > > len = SKB_DATA_ALIGN(len) +
> > > > > > SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
> > > > > >
> > > > > > + if (unlikely(!skb_page_frag_refill(len, &rq->alloc_frag, gfp)))
> > > > > > + return -ENOMEM;
> > > > > > +
> > > > > > buf = virtnet_rq_alloc(rq, len, gfp);
> > > > > > if (unlikely(!buf))
> > > > > > return -ENOMEM;
> > > > > > @@ -2521,6 +2521,12 @@ static int add_recvbuf_mergeable(struct virtnet_info *vi,
> > > > > > */
> > > > > > len = get_mergeable_buf_len(rq, &rq->mrg_avg_pkt_len, room);
> > > > > >
> > > > > > + if (unlikely(!skb_page_frag_refill(len + room, alloc_frag, gfp)))
> > > > > > + return -ENOMEM;
> > > > > > +
> > > > > > + if (!alloc_frag->offset && len + room + sizeof(struct virtnet_rq_dma) > alloc_frag->size)
> > > > > > + len -= sizeof(struct virtnet_rq_dma);
> > > > > > +
> > > > > > buf = virtnet_rq_alloc(rq, len + room, gfp);
> > > > > > if (unlikely(!buf))
> > > > > > return -ENOMEM;
> > > > > > --
> > > > > > 2.32.0.3.g01195cf9f
> > > > >
> > >
> >
>
