Xuan Zhuo
2022-Apr-23 14:36 UTC
[PATCH net] virtio_net: fix wrong buf address calculation when using xdp
On Sat, 23 Apr 2022 17:30:11 +0300, Nikolay Aleksandrov <razor at blackwall.org> wrote:> 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 <razor at blackwall.org> 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] <TASK> > >>> [ 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] </TASK> > >>> [ 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] <TASK> > >>> [ 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 <linux/bpf.h> > >>> #include <bpf/bpf_helpers.h> > >>> > >>> 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 at vger.kernel.org > >>> CC: Jason Wang <jasowang at redhat.com> > >>> CC: Xuan Zhuo <xuanzhuo at linux.alibaba.com> > >>> CC: Daniel Borkmann <daniel at iogearbox.net> > >>> CC: "Michael S. Tsirkin" <mst at redhat.com> > >>> CC: virtualization at lists.linux-foundation.org > >>> Fixes: 8fb7da9e9907 ("virtio_net: get build_skb() buf by data ptr") > >>> Signed-off-by: Nikolay Aleksandrov <razor at blackwall.org> > >>> --- > >>> 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).Yes, you are right.> > The above change guarantees that buf and p will be in the same pageHow can this be guaranteed? 1. For example, we applied for a 32k buffer first, and took away 1500 + hdr_len from the allocation. 2. set xdp 3. alloc for new buffer The buffer allocated in the third step must be unaligned, and it is entirely possible that p and buf are not on the same page. I fixed my previous patch. Thanks. diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c index 87838cbe38cf..d95e82255b94 100644 --- a/drivers/net/virtio_net.c +++ b/drivers/net/virtio_net.c @@ -1005,6 +1005,8 @@ static struct sk_buff *receive_mergeable(struct net_device *dev, * xdp.data_meta were adjusted */ len = xdp.data_end - xdp.data + vi->hdr_len + metasize; + + headroom = xdp.data - vi->hdr_len - metasize - (buf - headroom); /* We can only create skb based on xdp_page. */ if (unlikely(xdp_page != page)) { rcu_read_unlock(); @@ -1012,7 +1014,7 @@ 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); + headroom); return head_skb; } break;
Nikolay Aleksandrov
2022-Apr-23 14:58 UTC
[PATCH net] virtio_net: fix wrong buf address calculation when using xdp
On 23/04/2022 17:36, Xuan Zhuo wrote:> On Sat, 23 Apr 2022 17:30:11 +0300, Nikolay Aleksandrov <razor at blackwall.org> wrote: >> 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 <razor at blackwall.org> 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] <TASK> >>>>> [ 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] </TASK> >>>>> [ 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] <TASK> >>>>> [ 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 <linux/bpf.h> >>>>> #include <bpf/bpf_helpers.h> >>>>> >>>>> 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 at vger.kernel.org >>>>> CC: Jason Wang <jasowang at redhat.com> >>>>> CC: Xuan Zhuo <xuanzhuo at linux.alibaba.com> >>>>> CC: Daniel Borkmann <daniel at iogearbox.net> >>>>> CC: "Michael S. Tsirkin" <mst at redhat.com> >>>>> CC: virtualization at lists.linux-foundation.org >>>>> Fixes: 8fb7da9e9907 ("virtio_net: get build_skb() buf by data ptr") >>>>> Signed-off-by: Nikolay Aleksandrov <razor at blackwall.org> >>>>> --- >>>>> 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). > > Yes, you are right. > >> >> The above change guarantees that buf and p will be in the same page > > > How can this be guaranteed? > > 1. For example, we applied for a 32k buffer first, and took away 1500 + hdr_len > from the allocation. > 2. set xdp > 3. alloc for new buffer >p = page_address(page) + offset; buf = p & PAGE_MASK; // whatever page p lands in is where buf is set => p and buf are always in the same page, no?> The buffer allocated in the third step must be unaligned, and it is entirely > possible that p and buf are not on the same page. > > I fixed my previous patch. > > Thanks. > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c > index 87838cbe38cf..d95e82255b94 100644 > --- a/drivers/net/virtio_net.c > +++ b/drivers/net/virtio_net.c > @@ -1005,6 +1005,8 @@ static struct sk_buff *receive_mergeable(struct net_device *dev, > * xdp.data_meta were adjusted > */ > len = xdp.data_end - xdp.data + vi->hdr_len + metasize; > + > + headroom = xdp.data - vi->hdr_len - metasize - (buf - headroom);This is wrong, xdp.data isn't related to buf in the xdp_linearize_page() case.> /* We can only create skb based on xdp_page. */ > if (unlikely(xdp_page != page)) { > rcu_read_unlock(); > @@ -1012,7 +1014,7 @@ 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); > + headroom); > return head_skb; > } > break;