Bug 600203 - vhost net new userspace on old kernel: 95: falling back on userspace virtio
Summary: vhost net new userspace on old kernel: 95: falling back on userspace virtio
Alias: None
Product: Red Hat Enterprise Linux 6
Classification: Red Hat
Component: qemu-kvm   
(Show other bugs)
Version: 6.0
Hardware: All
OS: Linux
Target Milestone: rc
: ---
Assignee: Michael S. Tsirkin
QA Contact: Virtualization Bugs
Keywords: Regression, Reopened
Depends On:
TreeView+ depends on / blocked
Reported: 2010-06-04 06:52 UTC by Keqin Hong
Modified: 2013-01-09 22:40 UTC (History)
9 users (show)

Fixed In Version: qemu-kvm-
Doc Type: Bug Fix
Doc Text:
Story Points: ---
Clone Of:
Last Closed: 2010-11-10 21:25:28 UTC
Type: ---
Regression: ---
Mount Type: ---
Documentation: ---
Verified Versions:
Category: ---
oVirt Team: ---
RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: ---

Attachments (Terms of Use)

Description Keqin Hong 2010-06-04 06:52:00 UTC
Description of problem:
When starting a RHEL6 guest on RHEL6 host with vhost on, qemu monitor prompts "unable to start vhost net: 95: falling back on userspace virtio". Starting a RHEL5.5 guest doesn't have the issue.

Version-Release number of selected component (if applicable):

How reproducible:

# lsmod | grep vhost
vhost_net              22833  0 
macvtap                 7573  1 vhost_net
tun                    16295  1 vhost_net

# /usr/libexec/qemu-kvm -m 2G -smp 2 -drive file=RHEL6.0-64-virtio.qcow2,if=none,id=drive-virtio0,boot=on -device virtio-blk-pci,drive=drive-virtio0,id=virtio-blk-pci0,addr=0x3 -netdev tap,id=hostnet0,vhost=on -device virtio-net-pci,netdev=hostnet0,mac=76:00:40:3F:20:20,bus=pci.0,addr=0x4 -boot order=c,menu=on -uuid 17644ecc-d3a1-4d3c-a386-12daf50015f2 -rtc base=utc -no-hpet -rtc-td-hack -no-kvm-pit-reinjection -monitor stdio -cpu qemu64,+sse2 -balloon none -vnc :1

Steps to Reproduce:
1. Start VM with vhost on using CLI give above

Actual results:
qemu monitor prompts "unable to start vhost net: 95: falling back on userspace virtio"

Expected results:
no such prompt and vhost net should work fine for rhel6 guest.

Additional info:    
host info:
processor	: 0
vendor_id	: AuthenticAMD
cpu family	: 15
model		: 67
model name	: Dual-Core AMD Opteron(tm) Processor 1216
stepping	: 3
cpu MHz		: 1000.000
cache size	: 1024 KB
physical id	: 0
siblings	: 2
core id		: 0
cpu cores	: 2
apicid		: 0
initial apicid	: 0
fpu		: yes
fpu_exception	: yes
cpuid level	: 1
wp		: yes
flags		: fpu vme de pse tsc msr pae mce cx8 apic mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt rdtscp lm 3dnowext 3dnow rep_good extd_apicid pni cx16 lahf_lm cmp_legacy svm extapic cr8_legacy
bogomips	: 2009.36
TLB size	: 1024 4K pages
clflush size	: 64
cache_alignment	: 64
address sizes	: 40 bits physical, 48 bits virtual
power management: ts fid vid ttp tm stc

Comment 2 Keqin Hong 2010-06-04 06:57:25 UTC
guest info:

Comment 3 RHEL Product and Program Management 2010-06-04 09:23:10 UTC
This request was evaluated by Red Hat Product Management for inclusion in a Red
Hat Enterprise Linux major release.  Product Management has requested further
review of this request by Red Hat Engineering, for potential inclusion in a Red
Hat Enterprise Linux Major release.  This request is not yet committed for

Comment 4 Amit Shah 2010-06-04 09:23:41 UTC
What are the permissions you see on /dev/vhost-net? What are the SELinux permissions? Is your system configured for selinux to be in enforcing mode? Does disabling selinux make this work?

Comment 5 Keqin Hong 2010-06-04 09:48:31 UTC
# ll /dev/vhost-net 
crw-rw----. 1 root root 10, 233 Jun  4 10:58 /dev/vhost-net

# getenforce

I guess it is not related with permission or selinux, since the issue only happens on rhel6 guest not on rhel5

Comment 6 Amit Shah 2010-06-04 10:01:23 UTC
The output of ls -lZ /dev/vhost-net will give you the selinux labels as well.

vhost support is transparent to the guest, so the type of guest shouldn't be a concern.

If you're getting this only with rhel6 then it could be an MSI-related issue.

Comment 7 Keqin Hong 2010-06-04 10:08:26 UTC
# ls -lZ /dev/vhost-net 
crw-rw----. root root system_u:object_r:device_t:s0    /dev/vhost-net

Tested again on qemu-kvm-, the problem doesn't exist.
So a Regression.

Comment 8 Amit Shah 2010-06-04 10:12:03 UTC
Error code 95 is EOPNOTSUPP. mst should have a better idea on what's the failing route. It's surprising the same cmd line works fine for rhel5 guest.

Comment 9 Amit Shah 2010-06-04 10:18:56 UTC
The changelog for the .69 build had this bit related to virtio/vhost-net:

- kvm-virtio-utilize-PUBLISH_USED_IDX-feature.patch [bz#595287]
- Resolves: bz#595287
  (virtio net/vhost net speed enhancements from upstream kernel)

Comment 12 Keqin Hong 2010-06-07 03:32:32 UTC
The problem came in Comment 0 because the host testing kernel was 2.6.32-25.el6.x86_64. The problem doesn't exist on host kernel 2.6.32-30.el6.x86_64 or 2.6.32-33.el6.x86_64. Obviously, this is fixed by solving Bug 593158.

However, it is still strange if you look at Comment 7 where host kernel 2.6.32-25.el6.x86_64 with qemu-kvm- didn't have the problem.

If it is not a problem (that we don't care), I think I shall close this one as NOTABUG. Sorry for making this trouble to all of you.

Comment 13 Michael S. Tsirkin 2010-06-07 09:45:21 UTC
This is interesting in that rhel qemu should work on
upstream kernels. So this could be a bug, but not
a blocker and low priority.

I will change the title appropriately.

Comment 14 Keqin Hong 2010-06-07 09:52:53 UTC
Thanks, Michael.

Comment 17 Keqin Hong 2010-06-12 08:25:36 UTC
Verified on qemu-kvm- with either kernel-2.6.32-25.el6.x86_64 or  kernel-2.6.32-33.el6.x86_64. PASS

Comment 18 juzhang 2010-06-22 05:50:28 UTC
Tested on qemu-kvm-

When starting a RHEL6 guest on RHEL6 host with vhost on, qemu monitor prompts
"(qemu) Error binding host notifier: 28
unable to start vhost net: 28: falling back on userspace virtio".

/usr/libexec/qemu-kvm -usbdevice tablet -rtc-td-hack -m 2G -smp 2 -drive file=/root/zhangjunyi/rhel6_2.33_641.qcow2,if=virtio,boot=on,cache=none,format=qcow2,werror=stop,rerror=stop -drive file=/root/zhangjunyi/password.qcow2,if=virtio,format=qcow2,cache=none,werror=stop,rerror=stop -netdev tap,id=hostnet0,vhost=on -device virtio-net-pci,netdev=hostnet0,id=net0,mac=22:11:22:45:61:98 -netdev tap,id=hostnet1,vhost=on -device virtio-net-pci,netdev=hostnet1,id=net1,mac=22:11:22:45:62:98 -uuid `uuidgen` -cpu qemu64,+x2apic -device virtio-balloon-pci -boot order=cn,menu=on -monitor stdio -vnc :10 -qmp tcp:0:4444,server,nowait -qmp tcp:0:4445,server,nowait -name zhangjunyi

Please NOTE:
This issue only happened when boot two virtio nics,boot one virtio nic doesn't have the issue.

host info

guest info:

Comment 20 Michael S. Tsirkin 2010-06-22 11:01:00 UTC

*** This bug has been marked as a duplicate of bug 602262 ***

Comment 22 releng-rhel@redhat.com 2010-11-10 21:25:28 UTC
Red Hat Enterprise Linux 6.0 is now available and should resolve
the problem described in this bug report. This report is therefore being closed
with a resolution of CURRENTRELEASE. You may reopen this bug report if the
solution does not work for you.

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