This also happens for me with <cpu mode='custom' match='exact'> on a SandyBridge 2-socket.

When I try to force with <feature policy='require' name='nonstop_tsc'/> I get
error: internal error: Unknown CPU feature nonstop_tsc

Need this feature as part of a SAP HANA/KVM certification effort going on now.
Same version as submitter: qemu-kvm-rhev 2.3.0-31

Thanks,
Dave

(In reply to Guo, Zhiyi from comment #0)
> Description of problem:
> Cpu flag nonstop_tsc cannot pass through from host to guest with "-cpu host"
> option
> 
> Version-Release number of selected component (if applicable):
> kernel version(host&guest):3.10.0-326.el7.x86_64
> qemu version: qemu-kvm-rhev-2.3.0-31.el7.x86_64
> 
> How reproducible:
> 100% reproduce rate.
> 
> Steps to Reproduce:
> 1. qemu-kvm command: qemu-kvm -name rhel7.2 -m 6144 \
>         -cpu host\
>         -smp 2,cores=1,threads=2,sockets=2,maxcpus=4 \
>          -vga qxl\
>         -spice port=3001,disable-ticketing \
>         -device virtio-serial -chardev
> spicevmc,id=vdagent,debug=0,name=vdagent \
>         -serial unix:/tmp/m,server,nowait \
>         -device virtserialport,chardev=vdagent,name=com.redhat.spice.0 \
>         -drive
> file=rhev7_2_gpu_test.qcow2,if=none,id=drive-scsi-disk0,format=qcow2,
> cache=none,werror=stop,rerror=stop -device virtio-scsi-pci,id=scsi0 -device
> scsi-hd,drive=drive-scsi-disk0,bus=scsi0.0,scsi-id=0,lun=0,id=scsi-disk0,
> bootindex=1 \
>         -monitor stdio \
>         -netdev tap,id=idinWyYp,vhost=on -device
> virtio-net-pci,mac=42:ce:a9:d2:4d:d7,id=idlbq7eA,netdev=idinWyYp \
> 
> 2. login into rhev 7.2 system and check cpu flag by cat /proc/cpuinfo
> 
> Actual results:
> nonstop_tsc doesn't exist in flags of /proc/cpuinfo
> 
> Expected results:
> nonstop_tsc exists in flags of /proc/cpuinfo
> 
> Additional info:

-cpu host,+invtsc,migratable=no

exposes nonstop_tsc on

qemu-kvm-rhev-2.3.0-31.el7_2.17.x86_64

for me.

(In reply to djdumas from comment #2)
> This also happens for me with <cpu mode='custom' match='exact'> on a
> SandyBridge 2-socket.
> 
> When I try to force with <feature policy='require' name='nonstop_tsc'/> I get
> error: internal error: Unknown CPU feature nonstop_tsc
> 
> Need this feature as part of a SAP HANA/KVM certification effort going on
> now.
> Same version as submitter: qemu-kvm-rhev 2.3.0-31
> 
> Thanks,
> Dave

Dave,

I haven't tried it myself, but this is what the libvirt commit which introduced 
support for invtsc says:

commit fba6bc47cbcabbe08d42279691efb0dff3b9c997
Author: Ján Tomko <jtomko>
Date:   Tue May 6 13:55:44 2014 +0200

    Add invariant TSC cpu flag
    
    Add suport for invariant TSC flag (CPUID 0x80000007, bit 8 of EDX).
    If this flag is enabled, the TSC ticks at a constant rate across
    all ACPI P-, C- and T-states.
    
    This can be enabled by adding:
    <feature name='invtsc'/>
    to the <cpu> element.
    
    Migration and saving the domain does not work with this flag.
    
    QEMU support: http://git.qemu.org/?p=qemu.git;a=commitdiff;h=303752a
    
    The feature name "invtsc" differs from the name "" used by the linux kernel:
    https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/arch/x86/kernel/cpu/powerflags.c?id=30321c7b#n18

Perhaps you can try adding that option?

(In reply to Marcelo Tosatti from comment #4)

>     This can be enabled by adding:
>     <feature name='invtsc'/>
>     to the <cpu> element.
>     

....

> Perhaps you can try adding that option?

Hi Marcelo,

Nice call there - that worked, thank you.  I have nonstop_tsc in the guest now.

Dave

(In reply to djdumas from comment #5)
> (In reply to Marcelo Tosatti from comment #4)
> 
> >     This can be enabled by adding:
> >     <feature name='invtsc'/>
> >     to the <cpu> element.
> >     
> 
> ....
> 
> > Perhaps you can try adding that option?
> 
> Hi Marcelo,
> 
> Nice call there - that worked, thank you.  I have nonstop_tsc in the guest
> now.
> 
> Dave

Looks like this was not a bug afterall. Closing. 

Please reopen if there is still an issue. Thanks.