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Tsirkin" To: Xuan Zhuo Cc: Jason Wang , netdev@vger.kernel.org, Eugenio =?iso-8859-1?Q?P=E9rez?= , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , virtualization@lists.linux.dev, Si-Wei Liu , Darren Kenny Subject: Re: [PATCH net] virtio-net: fix overflow inside virtnet_rq_alloc Message-ID: <20240829034616-mutt-send-email-mst@kernel.org> References: <20240820071913.68004-1-xuanzhuo@linux.alibaba.com> <1724843499.0572476-1-xuanzhuo@linux.alibaba.com> <1724916360.9746847-3-xuanzhuo@linux.alibaba.com> <20240829033209-mutt-send-email-mst@kernel.org> <1724917087.5016513-1-xuanzhuo@linux.alibaba.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <1724917087.5016513-1-xuanzhuo@linux.alibaba.com> On Thu, Aug 29, 2024 at 03:38:07PM +0800, Xuan Zhuo wrote: > On Thu, 29 Aug 2024 03:35:58 -0400, "Michael S. Tsirkin" wrote: > > On Thu, Aug 29, 2024 at 03:26:00PM +0800, Xuan Zhuo wrote: > > > On Thu, 29 Aug 2024 12:51:31 +0800, Jason Wang wrote: > > > > On Wed, Aug 28, 2024 at 7:21 PM Xuan Zhuo wrote: > > > > > > > > > > On Tue, 27 Aug 2024 11:38:45 +0800, Jason Wang wrote: > > > > > > On Tue, Aug 20, 2024 at 3:19 PM 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. > > > > I don't exactly get it, when you say "only the first buffer of the frag > > is affected" what do you mean? Affected how? > > > I should say that if the frag is 32k, that is safe. > Only when that frag is 4k, that is not safe. > > Thanks. It looks like nothing changes when net.core.high_order_alloc_disable=0 (which is the default) but maybe I am missing something. It is worth testing performance with mtu set to 4k, just to make sure we did not miss anything. > > > > > > > > > > > > > > > I wonder instead of trying to make use of headroom, would it be > > > > > > simpler if we allocate dedicated arrays of virtnet_rq_dma？ > > > > > > > > > > Sorry for the late reply. My mailbox was full, so I missed the reply to this > > > > > thread. Thanks to Si-Wei for reminding me. > > > > > > > > > > If the virtnet_rq_dma is at the headroom, we can get the virtnet_rq_dma by buf. > > > > > > > > > > struct page *page = virt_to_head_page(buf); > > > > > > > > > > head = page_address(page); > > > > > > > > > > If we use a dedicated array, then we need pass the virtnet_rq_dma pointer to > > > > > virtio core, the array has the same size with the rx ring. > > > > > > > > > > The virtnet_rq_dma will be: > > > > > > > > > > struct virtnet_rq_dma { > > > > > dma_addr_t addr; > > > > > u32 ref; > > > > > u16 len; > > > > > u16 need_sync; > > > > > + void *buf; > > > > > }; > > > > > > > > > > That will be simpler. > > > > > > > > I'm not sure I understand here, did you mean using a dedicated array is simpler? > > > > > > I found the old version(that used a dedicated array): > > > > > > http://lore.kernel.org/all/20230710034237.12391-11-xuanzhuo@linux.alibaba.com > > > > > > If you think that is ok, I can port a new version based that. > > > > > > Thanks. > > > > > > > That one got a bunch of comments that likely still apply. > > And this looks like a much bigger change than what this > > patch proposes. > > > > > > > > > > > > > > > > > > > > > > > Btw, I see it has a need_sync, I wonder if it can help for performance > > > > > > or not? If not, any reason to keep that? > > > > > > > > > > I think yes, we can skip the cpu sync when we do not need it. > > > > > > > > I meant it looks to me the needs_sync is not necessary in the > > > > structure as we can call need_sync() any time if we had dma addr. > > > > > > > > Thanks > > > > > > > > > > > > > > Thanks. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Fixes: f9dac92ba908 ("virtio_ring: enable premapped mode whatever use_dma_api") > > > > > > > Reported-by: "Si-Wei Liu" > > > > > > > Closes: http://lore.kernel.org/all/8b20cc28-45a9-4643-8e87-ba164a540c0a@oracle.com > > > > > > > Signed-off-by: Xuan Zhuo > > > > > > > --- > > > > > > > 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 > > > > > > > > > > > > Thanks > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > >