[Bug 219161] New: VM with virtio-net doesn't receive large UDP packets (e.g 65507 bytes) from host

[Bug 219161] New: VM with virtio-net doesn't receive large UDP packets (e.g 65507 bytes) from host

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=219161

            Bug ID: 219161
           Summary: VM with virtio-net doesn't receive large UDP packets
                    (e.g 65507 bytes) from host
           Product: Virtualization
           Version: unspecified
          Hardware: All
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P3
         Component: kvm
          Assignee: virtualization_kvm@kernel-bugs.osdl.org
          Reporter: wquan@redhat.com
        Regression: No

Description：
Large UDP packets (e.g 65507 bytes) are not received in VM using virtio-net
when sent from host to VM, while smaller packets are received successfully. 

The issue occurs with or without vhost enabled, and can be reproduce with
6.5.0-rc5+

Build Date & Hardware:
   6.11.0-rc2+ (d4560686726f7a357922f300fc81f5964be8df04 Merge tag 'for_linus'
of git://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost) 

Steps to Reproduce:

1. boot a vm from kvm

 -device '{"id": "pcie-root-port-3", "port": 3, "driver": "pcie-root-port",
"addr": "0x1.0x3", "bus": "pcie.0", "chassis": 4}' \
 -device '{"driver": "virtio-net-pci", "mac": "9a:59:9c:26:c7:52", "id":
"id1GUehY", "netdev": "idIlyxUy", "bus": "pcie-root-port-3", "addr": "0x0"}' \
 -netdev '{"id": "idIlyxUy", "type": "tap", "vhost": true}'  \

2. on vm, disable iptables and nftables. then run "netserver"
3. on host
 # netperf -H 192.168.58.21 -t UDP_STREAM -- -m  65507
MIGRATED UDP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 192.168.58.21
() port 0 AF_INET : interval : demo
Socket  Message  Elapsed      Messages
Size    Size     Time         Okay Errors   Throughput
bytes   bytes    secs            #      #   10^6bits/sec

212992   65507   10.00      385575      0    20206.13
212992           10.00          86              4.51

# netperf -H 192.168.58.21 -t UDP_STREAM -- -m  2800
MIGRATED UDP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 192.168.58.21
() port 0 AF_INET : interval : demo
Socket  Message  Elapsed      Messages
Size    Size     Time         Okay Errors   Throughput
bytes   bytes    secs            #      #   10^6bits/sec

212992    2800   10.00     5125735      0    11481.60
212992           10.00     3562544           7980.07

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Re: [Bug 219161] New: VM with virtio-net doesn't receive large UDP packets (e.g 65507 bytes) from host

[Sean Christopherson]

On Thu, Aug 15, 2024, bugzilla-daemon@kernel.org wrote:
> Large UDP packets (e.g 65507 bytes) are not received in VM using virtio-net
> when sent from host to VM, while smaller packets are received successfully. 
> 
> The issue occurs with or without vhost enabled, and can be reproduce with
> 6.5.0-rc5+

Is this 100% reproducible?  And did it first show up in 6.5-rc5, i.e. does
everything work as expected in 6.5-rc4?  If so, bisecting will likely get you a
fast root cause and fix, unless someone happens to know a likely suspect.

[Bug 219161] VM with virtio-net doesn't receive large UDP packets (e.g 65507 bytes) from host

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=219161

--- Comment #1 from Sean Christopherson (seanjc@google.com) ---
On Thu, Aug 15, 2024, bugzilla-daemon@kernel.org wrote:
> Large UDP packets (e.g 65507 bytes) are not received in VM using virtio-net
> when sent from host to VM, while smaller packets are received successfully. 
> 
> The issue occurs with or without vhost enabled, and can be reproduce with
> 6.5.0-rc5+

Is this 100% reproducible?  And did it first show up in 6.5-rc5, i.e. does
everything work as expected in 6.5-rc4?  If so, bisecting will likely get you a
fast root cause and fix, unless someone happens to know a likely suspect.

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[Bug 219161] VM with virtio-net doesn't receive large UDP packets (e.g 65507 bytes) from host

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=219161

--- Comment #2 from wenli quan (wquan@redhat.com) ---
(In reply to Sean Christopherson from comment #1)
> On Thu, Aug 15, 2024, bugzilla-daemon@kernel.org wrote:
> > Large UDP packets (e.g 65507 bytes) are not received in VM using virtio-net
> > when sent from host to VM, while smaller packets are received successfully. 
> > 
> > The issue occurs with or without vhost enabled, and can be reproduce with
> > 6.5.0-rc5+
> 
> Is this 100% reproducible?  And did it first show up in 6.5-rc5, i.e. does
> everything work as expected in 6.5-rc4?  If so, bisecting will likely get
> you a
> fast root cause and fix, unless someone happens to know a likely suspect.

Yes, it's 100% reproducible. I also tried with a very old version alongside
6.5-rc5, and the issue still occurs. Unfortunately, I'm not sure which version
could be good, so I haven't started bisecting yet.

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