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[87.243.81.1]) by smtp.gmail.com with ESMTPSA id n14-20020a50934e000000b0042053e79386sm2267624eda.91.2022.04.23.07.30.11 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 23 Apr 2022 07:30:12 -0700 (PDT) Message-ID: Date: Sat, 23 Apr 2022 17:30:11 +0300 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.7.0 Subject: Re: [PATCH net] virtio_net: fix wrong buf address calculation when using xdp Content-Language: en-US From: Nikolay Aleksandrov To: Xuan Zhuo Cc: kuba@kernel.org, davem@davemloft.net, stable@vger.kernel.org, Jason Wang , Daniel Borkmann , "Michael S. Tsirkin" , virtualization@lists.linux-foundation.org, netdev@vger.kernel.org References: <20220423112612.2292774-1-razor@blackwall.org> <1650720683.8168066-1-xuanzhuo@linux.alibaba.com> <8d511a16-8d69-82b1-48a1-24de3a592aef@blackwall.org> In-Reply-To: <8d511a16-8d69-82b1-48a1-24de3a592aef@blackwall.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 23/04/2022 17:16, Nikolay Aleksandrov wrote: > On 23/04/2022 16:31, Xuan Zhuo wrote: >> On Sat, 23 Apr 2022 14:26:12 +0300, Nikolay Aleksandrov wrote: >>> We received a report[1] of kernel crashes when Cilium is used in XDP >>> mode with virtio_net after updating to newer kernels. After >>> investigating the reason it turned out that when using mergeable bufs >>> with an XDP program which adjusts xdp.data or xdp.data_meta page_to_buf() >>> calculates the build_skb address wrong because the offset can become less >>> than the headroom so it gets the address of the previous page (-X bytes >>> depending on how lower offset is): >>> page_to_skb: page addr ffff9eb2923e2000 buf ffff9eb2923e1ffc offset 252 headroom 256 >>> >>> This is a pr_err() I added in the beginning of page_to_skb which clearly >>> shows offset that is less than headroom by adding 4 bytes of metadata >>> via an xdp prog. The calculations done are: >>> receive_mergeable(): >>> headroom = VIRTIO_XDP_HEADROOM; // VIRTIO_XDP_HEADROOM == 256 bytes >>> offset = xdp.data - page_address(xdp_page) - >>> vi->hdr_len - metasize; >>> >>> page_to_skb(): >>> p = page_address(page) + offset; >>> ... >>> buf = p - headroom; >>> >>> Now buf goes -4 bytes from the page's starting address as can be seen >>> above which is set as skb->head and skb->data by build_skb later. Depending >>> on what's done with the skb (when it's freed most often) we get all kinds >>> of corruptions and BUG_ON() triggers in mm[2]. The story of the faulty >>> commit is interesting because the patch was sent and applied twice (it >>> seems the first one got lost during merge back in 5.13 window). The >>> first version of the patch that was applied as: >>> commit 7bf64460e3b2 ("virtio-net: get build_skb() buf by data ptr") >>> was actually correct because it calculated the page starting address >>> without relying on offset or headroom, but then the second version that >>> was applied as: >>> commit 8fb7da9e9907 ("virtio_net: get build_skb() buf by data ptr") >>> was wrong and added the above calculation. >>> An example xdp prog[3] is below. >>> >>> [1] https://github.com/cilium/cilium/issues/19453 >>> >>> [2] Two of the many traces: >>> [ 40.437400] BUG: Bad page state in process swapper/0 pfn:14940 >>> [ 40.916726] BUG: Bad page state in process systemd-resolve pfn:053b7 >>> [ 41.300891] kernel BUG at include/linux/mm.h:720! >>> [ 41.301801] invalid opcode: 0000 [#1] PREEMPT SMP NOPTI >>> [ 41.302784] CPU: 1 PID: 1181 Comm: kubelet Kdump: loaded Tainted: G B W 5.18.0-rc1+ #37 >>> [ 41.304458] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.15.0-1.fc35 04/01/2014 >>> [ 41.306018] RIP: 0010:page_frag_free+0x79/0xe0 >>> [ 41.306836] Code: 00 00 75 ea 48 8b 07 a9 00 00 01 00 74 e0 48 8b 47 48 48 8d 50 ff a8 01 48 0f 45 fa eb d0 48 c7 c6 18 b8 30 a6 e8 d7 f8 fc ff <0f> 0b 48 8d 78 ff eb bc 48 8b 07 a9 00 00 01 00 74 3a 66 90 0f b6 >>> [ 41.310235] RSP: 0018:ffffac05c2a6bc78 EFLAGS: 00010292 >>> [ 41.311201] RAX: 000000000000003e RBX: 0000000000000000 RCX: 0000000000000000 >>> [ 41.312502] RDX: 0000000000000001 RSI: ffffffffa6423004 RDI: 00000000ffffffff >>> [ 41.313794] RBP: ffff993c98823600 R08: 0000000000000000 R09: 00000000ffffdfff >>> [ 41.315089] R10: ffffac05c2a6ba68 R11: ffffffffa698ca28 R12: ffff993c98823600 >>> [ 41.316398] R13: ffff993c86311ebc R14: 0000000000000000 R15: 000000000000005c >>> [ 41.317700] FS: 00007fe13fc56740(0000) GS:ffff993cdd900000(0000) knlGS:0000000000000000 >>> [ 41.319150] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >>> [ 41.320152] CR2: 000000c00008a000 CR3: 0000000014908000 CR4: 0000000000350ee0 >>> [ 41.321387] Call Trace: >>> [ 41.321819] >>> [ 41.322193] skb_release_data+0x13f/0x1c0 >>> [ 41.322902] __kfree_skb+0x20/0x30 >>> [ 41.343870] tcp_recvmsg_locked+0x671/0x880 >>> [ 41.363764] tcp_recvmsg+0x5e/0x1c0 >>> [ 41.384102] inet_recvmsg+0x42/0x100 >>> [ 41.406783] ? sock_recvmsg+0x1d/0x70 >>> [ 41.428201] sock_read_iter+0x84/0xd0 >>> [ 41.445592] ? 0xffffffffa3000000 >>> [ 41.462442] new_sync_read+0x148/0x160 >>> [ 41.479314] ? 0xffffffffa3000000 >>> [ 41.496937] vfs_read+0x138/0x190 >>> [ 41.517198] ksys_read+0x87/0xc0 >>> [ 41.535336] do_syscall_64+0x3b/0x90 >>> [ 41.551637] entry_SYSCALL_64_after_hwframe+0x44/0xae >>> [ 41.568050] RIP: 0033:0x48765b >>> [ 41.583955] Code: e8 4a 35 fe ff eb 88 cc cc cc cc cc cc cc cc e8 fb 7a fe ff 48 8b 7c 24 10 48 8b 74 24 18 48 8b 54 24 20 48 8b 44 24 08 0f 05 <48> 3d 01 f0 ff ff 76 20 48 c7 44 24 28 ff ff ff ff 48 c7 44 24 30 >>> [ 41.632818] RSP: 002b:000000c000a2f5b8 EFLAGS: 00000212 ORIG_RAX: 0000000000000000 >>> [ 41.664588] RAX: ffffffffffffffda RBX: 000000c000062000 RCX: 000000000048765b >>> [ 41.681205] RDX: 0000000000005e54 RSI: 000000c000e66000 RDI: 0000000000000016 >>> [ 41.697164] RBP: 000000c000a2f608 R08: 0000000000000001 R09: 00000000000001b4 >>> [ 41.713034] R10: 00000000000000b6 R11: 0000000000000212 R12: 00000000000000e9 >>> [ 41.728755] R13: 0000000000000001 R14: 000000c000a92000 R15: ffffffffffffffff >>> [ 41.744254] >>> [ 41.758585] Modules linked in: br_netfilter bridge veth netconsole virtio_net >>> >>> and >>> >>> [ 33.524802] BUG: Bad page state in process systemd-network pfn:11e60 >>> [ 33.528617] page ffffe05dc0147b00 ffffe05dc04e7a00 ffff8ae9851ec000 (1) len 82 offset 252 metasize 4 hroom 0 hdr_len 12 data ffff8ae9851ec10c data_meta ffff8ae9851ec108 data_end ffff8ae9851ec14e >>> [ 33.529764] page:000000003792b5ba refcount:0 mapcount:-512 mapping:0000000000000000 index:0x0 pfn:0x11e60 >>> [ 33.532463] flags: 0xfffffc0000000(node=0|zone=1|lastcpupid=0x1fffff) >>> [ 33.532468] raw: 000fffffc0000000 0000000000000000 dead000000000122 0000000000000000 >>> [ 33.532470] raw: 0000000000000000 0000000000000000 00000000fffffdff 0000000000000000 >>> [ 33.532471] page dumped because: nonzero mapcount >>> [ 33.532472] Modules linked in: br_netfilter bridge veth netconsole virtio_net >>> [ 33.532479] CPU: 0 PID: 791 Comm: systemd-network Kdump: loaded Not tainted 5.18.0-rc1+ #37 >>> [ 33.532482] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.15.0-1.fc35 04/01/2014 >>> [ 33.532484] Call Trace: >>> [ 33.532496] >>> [ 33.532500] dump_stack_lvl+0x45/0x5a >>> [ 33.532506] bad_page.cold+0x63/0x94 >>> [ 33.532510] free_pcp_prepare+0x290/0x420 >>> [ 33.532515] free_unref_page+0x1b/0x100 >>> [ 33.532518] skb_release_data+0x13f/0x1c0 >>> [ 33.532524] kfree_skb_reason+0x3e/0xc0 >>> [ 33.532527] ip6_mc_input+0x23c/0x2b0 >>> [ 33.532531] ip6_sublist_rcv_finish+0x83/0x90 >>> [ 33.532534] ip6_sublist_rcv+0x22b/0x2b0 >>> >>> [3] XDP program to reproduce(xdp_pass.c): >>> #include >>> #include >>> >>> SEC("xdp_pass") >>> int xdp_pkt_pass(struct xdp_md *ctx) >>> { >>> bpf_xdp_adjust_head(ctx, -(int)32); >>> return XDP_PASS; >>> } >>> >>> char _license[] SEC("license") = "GPL"; >>> >>> compile: clang -O2 -g -Wall -target bpf -c xdp_pass.c -o xdp_pass.o >>> load on virtio_net: ip link set enp1s0 xdpdrv obj xdp_pass.o sec xdp_pass >>> >>> CC: stable@vger.kernel.org >>> CC: Jason Wang >>> CC: Xuan Zhuo >>> CC: Daniel Borkmann >>> CC: "Michael S. Tsirkin" >>> CC: virtualization@lists.linux-foundation.org >>> Fixes: 8fb7da9e9907 ("virtio_net: get build_skb() buf by data ptr") >>> Signed-off-by: Nikolay Aleksandrov >>> --- >>> drivers/net/virtio_net.c | 8 ++++++-- >>> 1 file changed, 6 insertions(+), 2 deletions(-) >>> >>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c >>> index 87838cbe38cf..0687dd88e97f 100644 >>> --- a/drivers/net/virtio_net.c >>> +++ b/drivers/net/virtio_net.c >>> @@ -434,9 +434,13 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi, >>> * Buffers with headroom use PAGE_SIZE as alloc size, see >>> * add_recvbuf_mergeable() + get_mergeable_buf_len() >>> */ >>> - truesize = headroom ? PAGE_SIZE : truesize; >>> + if (headroom) { >>> + truesize = PAGE_SIZE; >>> + buf = (char *)((unsigned long)p & PAGE_MASK); >> >> The reason for not doing this is that buf and p may not be on the same page, and >> buf is probably not page-aligned. >> >> The implementation of virtio-net merge is add_recvbuf_mergeable(), which >> allocates a large block of memory at one time, and allocates from it each time. >> Although in xdp mode, each allocation is page_size, it does not guarantee that >> each allocation is page-aligned . >> >> The problem here is that the value of headroom is wrong, the package is >> structured like this: >> >> from device | headroom | virtio-net hdr | data | >> after xdp | headroom | virtio-net hdr | meta | data | > > You're free to push data back (not necessarily through meta). > You don't have virtio-net hdr for the xdp case (hdr_valid is false there). > >> >> The page_address(page) + offset we pass to page_to_skb() points to the >> virtio-net hdr. >> >> So I think it might be better to change it this way. >> >> Thanks. >> >> >> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c >> index 87838cbe38cf..086ae835ec86 100644 >> --- a/drivers/net/virtio_net.c >> +++ b/drivers/net/virtio_net.c >> @@ -1012,7 +1012,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev, >> head_skb = page_to_skb(vi, rq, xdp_page, offset, >> len, PAGE_SIZE, false, >> metasize, >> - VIRTIO_XDP_HEADROOM); >> + VIRTIO_XDP_HEADROOM - metazie); >> return head_skb; >> } >> break; > > That patch doesn't fix it, as I said with xdp you can move both data and data_meta. > So just doing that would take care of the meta, but won't take care of moving data. > Also it doesn't take care of the case where page_to_skb() is called with the original page i.e. when we already have headroom, so we hit the next/standard page_to_skb() call (xdp_page == page). The above change guarantees that buf and p will be in the same page and the skb_reserve() call will make skb->data point to p - buf, i.e. to the beginning of the valid data in that page. Unfortunately the new headroom will not be correct if it is a frag, it will be longer. 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[87.243.81.1]) by smtp.gmail.com with ESMTPSA id n14-20020a50934e000000b0042053e79386sm2267624eda.91.2022.04.23.07.30.11 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 23 Apr 2022 07:30:12 -0700 (PDT) Message-ID: Date: Sat, 23 Apr 2022 17:30:11 +0300 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.7.0 Subject: Re: [PATCH net] virtio_net: fix wrong buf address calculation when using xdp Content-Language: en-US From: Nikolay Aleksandrov To: Xuan Zhuo References: <20220423112612.2292774-1-razor@blackwall.org> <1650720683.8168066-1-xuanzhuo@linux.alibaba.com> <8d511a16-8d69-82b1-48a1-24de3a592aef@blackwall.org> In-Reply-To: <8d511a16-8d69-82b1-48a1-24de3a592aef@blackwall.org> Cc: Daniel Borkmann , "Michael S. Tsirkin" , netdev@vger.kernel.org, stable@vger.kernel.org, virtualization@lists.linux-foundation.org, kuba@kernel.org, davem@davemloft.net X-BeenThere: virtualization@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Linux virtualization List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: virtualization-bounces@lists.linux-foundation.org Sender: "Virtualization" On 23/04/2022 17:16, Nikolay Aleksandrov wrote: > On 23/04/2022 16:31, Xuan Zhuo wrote: >> On Sat, 23 Apr 2022 14:26:12 +0300, Nikolay Aleksandrov wrote: >>> We received a report[1] of kernel crashes when Cilium is used in XDP >>> mode with virtio_net after updating to newer kernels. After >>> investigating the reason it turned out that when using mergeable bufs >>> with an XDP program which adjusts xdp.data or xdp.data_meta page_to_buf() >>> calculates the build_skb address wrong because the offset can become less >>> than the headroom so it gets the address of the previous page (-X bytes >>> depending on how lower offset is): >>> page_to_skb: page addr ffff9eb2923e2000 buf ffff9eb2923e1ffc offset 252 headroom 256 >>> >>> This is a pr_err() I added in the beginning of page_to_skb which clearly >>> shows offset that is less than headroom by adding 4 bytes of metadata >>> via an xdp prog. The calculations done are: >>> receive_mergeable(): >>> headroom = VIRTIO_XDP_HEADROOM; // VIRTIO_XDP_HEADROOM == 256 bytes >>> offset = xdp.data - page_address(xdp_page) - >>> vi->hdr_len - metasize; >>> >>> page_to_skb(): >>> p = page_address(page) + offset; >>> ... >>> buf = p - headroom; >>> >>> Now buf goes -4 bytes from the page's starting address as can be seen >>> above which is set as skb->head and skb->data by build_skb later. Depending >>> on what's done with the skb (when it's freed most often) we get all kinds >>> of corruptions and BUG_ON() triggers in mm[2]. The story of the faulty >>> commit is interesting because the patch was sent and applied twice (it >>> seems the first one got lost during merge back in 5.13 window). The >>> first version of the patch that was applied as: >>> commit 7bf64460e3b2 ("virtio-net: get build_skb() buf by data ptr") >>> was actually correct because it calculated the page starting address >>> without relying on offset or headroom, but then the second version that >>> was applied as: >>> commit 8fb7da9e9907 ("virtio_net: get build_skb() buf by data ptr") >>> was wrong and added the above calculation. >>> An example xdp prog[3] is below. >>> >>> [1] https://github.com/cilium/cilium/issues/19453 >>> >>> [2] Two of the many traces: >>> [ 40.437400] BUG: Bad page state in process swapper/0 pfn:14940 >>> [ 40.916726] BUG: Bad page state in process systemd-resolve pfn:053b7 >>> [ 41.300891] kernel BUG at include/linux/mm.h:720! >>> [ 41.301801] invalid opcode: 0000 [#1] PREEMPT SMP NOPTI >>> [ 41.302784] CPU: 1 PID: 1181 Comm: kubelet Kdump: loaded Tainted: G B W 5.18.0-rc1+ #37 >>> [ 41.304458] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.15.0-1.fc35 04/01/2014 >>> [ 41.306018] RIP: 0010:page_frag_free+0x79/0xe0 >>> [ 41.306836] Code: 00 00 75 ea 48 8b 07 a9 00 00 01 00 74 e0 48 8b 47 48 48 8d 50 ff a8 01 48 0f 45 fa eb d0 48 c7 c6 18 b8 30 a6 e8 d7 f8 fc ff <0f> 0b 48 8d 78 ff eb bc 48 8b 07 a9 00 00 01 00 74 3a 66 90 0f b6 >>> [ 41.310235] RSP: 0018:ffffac05c2a6bc78 EFLAGS: 00010292 >>> [ 41.311201] RAX: 000000000000003e RBX: 0000000000000000 RCX: 0000000000000000 >>> [ 41.312502] RDX: 0000000000000001 RSI: ffffffffa6423004 RDI: 00000000ffffffff >>> [ 41.313794] RBP: ffff993c98823600 R08: 0000000000000000 R09: 00000000ffffdfff >>> [ 41.315089] R10: ffffac05c2a6ba68 R11: ffffffffa698ca28 R12: ffff993c98823600 >>> [ 41.316398] R13: ffff993c86311ebc R14: 0000000000000000 R15: 000000000000005c >>> [ 41.317700] FS: 00007fe13fc56740(0000) GS:ffff993cdd900000(0000) knlGS:0000000000000000 >>> [ 41.319150] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >>> [ 41.320152] CR2: 000000c00008a000 CR3: 0000000014908000 CR4: 0000000000350ee0 >>> [ 41.321387] Call Trace: >>> [ 41.321819] >>> [ 41.322193] skb_release_data+0x13f/0x1c0 >>> [ 41.322902] __kfree_skb+0x20/0x30 >>> [ 41.343870] tcp_recvmsg_locked+0x671/0x880 >>> [ 41.363764] tcp_recvmsg+0x5e/0x1c0 >>> [ 41.384102] inet_recvmsg+0x42/0x100 >>> [ 41.406783] ? sock_recvmsg+0x1d/0x70 >>> [ 41.428201] sock_read_iter+0x84/0xd0 >>> [ 41.445592] ? 0xffffffffa3000000 >>> [ 41.462442] new_sync_read+0x148/0x160 >>> [ 41.479314] ? 0xffffffffa3000000 >>> [ 41.496937] vfs_read+0x138/0x190 >>> [ 41.517198] ksys_read+0x87/0xc0 >>> [ 41.535336] do_syscall_64+0x3b/0x90 >>> [ 41.551637] entry_SYSCALL_64_after_hwframe+0x44/0xae >>> [ 41.568050] RIP: 0033:0x48765b >>> [ 41.583955] Code: e8 4a 35 fe ff eb 88 cc cc cc cc cc cc cc cc e8 fb 7a fe ff 48 8b 7c 24 10 48 8b 74 24 18 48 8b 54 24 20 48 8b 44 24 08 0f 05 <48> 3d 01 f0 ff ff 76 20 48 c7 44 24 28 ff ff ff ff 48 c7 44 24 30 >>> [ 41.632818] RSP: 002b:000000c000a2f5b8 EFLAGS: 00000212 ORIG_RAX: 0000000000000000 >>> [ 41.664588] RAX: ffffffffffffffda RBX: 000000c000062000 RCX: 000000000048765b >>> [ 41.681205] RDX: 0000000000005e54 RSI: 000000c000e66000 RDI: 0000000000000016 >>> [ 41.697164] RBP: 000000c000a2f608 R08: 0000000000000001 R09: 00000000000001b4 >>> [ 41.713034] R10: 00000000000000b6 R11: 0000000000000212 R12: 00000000000000e9 >>> [ 41.728755] R13: 0000000000000001 R14: 000000c000a92000 R15: ffffffffffffffff >>> [ 41.744254] >>> [ 41.758585] Modules linked in: br_netfilter bridge veth netconsole virtio_net >>> >>> and >>> >>> [ 33.524802] BUG: Bad page state in process systemd-network pfn:11e60 >>> [ 33.528617] page ffffe05dc0147b00 ffffe05dc04e7a00 ffff8ae9851ec000 (1) len 82 offset 252 metasize 4 hroom 0 hdr_len 12 data ffff8ae9851ec10c data_meta ffff8ae9851ec108 data_end ffff8ae9851ec14e >>> [ 33.529764] page:000000003792b5ba refcount:0 mapcount:-512 mapping:0000000000000000 index:0x0 pfn:0x11e60 >>> [ 33.532463] flags: 0xfffffc0000000(node=0|zone=1|lastcpupid=0x1fffff) >>> [ 33.532468] raw: 000fffffc0000000 0000000000000000 dead000000000122 0000000000000000 >>> [ 33.532470] raw: 0000000000000000 0000000000000000 00000000fffffdff 0000000000000000 >>> [ 33.532471] page dumped because: nonzero mapcount >>> [ 33.532472] Modules linked in: br_netfilter bridge veth netconsole virtio_net >>> [ 33.532479] CPU: 0 PID: 791 Comm: systemd-network Kdump: loaded Not tainted 5.18.0-rc1+ #37 >>> [ 33.532482] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.15.0-1.fc35 04/01/2014 >>> [ 33.532484] Call Trace: >>> [ 33.532496] >>> [ 33.532500] dump_stack_lvl+0x45/0x5a >>> [ 33.532506] bad_page.cold+0x63/0x94 >>> [ 33.532510] free_pcp_prepare+0x290/0x420 >>> [ 33.532515] free_unref_page+0x1b/0x100 >>> [ 33.532518] skb_release_data+0x13f/0x1c0 >>> [ 33.532524] kfree_skb_reason+0x3e/0xc0 >>> [ 33.532527] ip6_mc_input+0x23c/0x2b0 >>> [ 33.532531] ip6_sublist_rcv_finish+0x83/0x90 >>> [ 33.532534] ip6_sublist_rcv+0x22b/0x2b0 >>> >>> [3] XDP program to reproduce(xdp_pass.c): >>> #include >>> #include >>> >>> SEC("xdp_pass") >>> int xdp_pkt_pass(struct xdp_md *ctx) >>> { >>> bpf_xdp_adjust_head(ctx, -(int)32); >>> return XDP_PASS; >>> } >>> >>> char _license[] SEC("license") = "GPL"; >>> >>> compile: clang -O2 -g -Wall -target bpf -c xdp_pass.c -o xdp_pass.o >>> load on virtio_net: ip link set enp1s0 xdpdrv obj xdp_pass.o sec xdp_pass >>> >>> CC: stable@vger.kernel.org >>> CC: Jason Wang >>> CC: Xuan Zhuo >>> CC: Daniel Borkmann >>> CC: "Michael S. Tsirkin" >>> CC: virtualization@lists.linux-foundation.org >>> Fixes: 8fb7da9e9907 ("virtio_net: get build_skb() buf by data ptr") >>> Signed-off-by: Nikolay Aleksandrov >>> --- >>> drivers/net/virtio_net.c | 8 ++++++-- >>> 1 file changed, 6 insertions(+), 2 deletions(-) >>> >>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c >>> index 87838cbe38cf..0687dd88e97f 100644 >>> --- a/drivers/net/virtio_net.c >>> +++ b/drivers/net/virtio_net.c >>> @@ -434,9 +434,13 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi, >>> * Buffers with headroom use PAGE_SIZE as alloc size, see >>> * add_recvbuf_mergeable() + get_mergeable_buf_len() >>> */ >>> - truesize = headroom ? PAGE_SIZE : truesize; >>> + if (headroom) { >>> + truesize = PAGE_SIZE; >>> + buf = (char *)((unsigned long)p & PAGE_MASK); >> >> The reason for not doing this is that buf and p may not be on the same page, and >> buf is probably not page-aligned. >> >> The implementation of virtio-net merge is add_recvbuf_mergeable(), which >> allocates a large block of memory at one time, and allocates from it each time. >> Although in xdp mode, each allocation is page_size, it does not guarantee that >> each allocation is page-aligned . >> >> The problem here is that the value of headroom is wrong, the package is >> structured like this: >> >> from device | headroom | virtio-net hdr | data | >> after xdp | headroom | virtio-net hdr | meta | data | > > You're free to push data back (not necessarily through meta). > You don't have virtio-net hdr for the xdp case (hdr_valid is false there). > >> >> The page_address(page) + offset we pass to page_to_skb() points to the >> virtio-net hdr. >> >> So I think it might be better to change it this way. >> >> Thanks. >> >> >> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c >> index 87838cbe38cf..086ae835ec86 100644 >> --- a/drivers/net/virtio_net.c >> +++ b/drivers/net/virtio_net.c >> @@ -1012,7 +1012,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev, >> head_skb = page_to_skb(vi, rq, xdp_page, offset, >> len, PAGE_SIZE, false, >> metasize, >> - VIRTIO_XDP_HEADROOM); >> + VIRTIO_XDP_HEADROOM - metazie); >> return head_skb; >> } >> break; > > That patch doesn't fix it, as I said with xdp you can move both data and data_meta. > So just doing that would take care of the meta, but won't take care of moving data. > Also it doesn't take care of the case where page_to_skb() is called with the original page i.e. when we already have headroom, so we hit the next/standard page_to_skb() call (xdp_page == page). The above change guarantees that buf and p will be in the same page and the skb_reserve() call will make skb->data point to p - buf, i.e. to the beginning of the valid data in that page. Unfortunately the new headroom will not be correct if it is a frag, it will be longer. _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization