One probably needs to apply workaround to WS2016 for broken by default CPU hotplug
 https://bugzilla.redhat.com/show_bug.cgi?id=1377155#c17
to trigger the crash, otherwise windows won't even try to online hotplugged cpu.

Bug reproduces in both KVM and TCG modes, and according to KVM trace, hotplugged CPU wakes up but then during bring up it goes into triple fault and guest reboots.

Googling also shows that the same regression happens on vmware hosts.

There is latest (announced June 11) cumulative update for 2016 KB4503267.
It was probably was expected to solve this problem and reboot does not happen upon cpu-add.
But the CPU does not work, PnP operation does not finish and the system stops working correctly.
I've running the qemu as '-smp 2,maxcpus=4,sockets=4,cores=1,threads=1', then add 3rd cpu as 'cpu-add 2'
msinfo32 does not work, taskmgr does not show tasks, shutdown/reboot stucks.
All this happens when memory size set to 2G(2048M)
When it is set to 2080M - cpu is added correctly.
Note that the same thing happens with 'core' server (without desktop experience), which does not declare 2G as minimal amount of memory.
I'm going to open a support ticket at Microsoft.

Support request 119061321000566

According to Microsoft feedback: 
"the issue initially reported is in effect by a bug that affect Windows 2016 (it was solved in Windows 2019 in the KB4482887) that needs to be solved as soon as possible. According my notes from the develop team the solution for this bug is planned to be published with the last hotfix KB next month of August"
So, we will put this on hold till August and will check it with next cumulative update of 2016.

Reopening it to RHEL8, to keep track on a fix from Microsoft side.

Is it even realistic scenario when Windows machine has only 2G of RAM? I see they recommend minimum 512M. But from my experience, usually it takes 4G+ to make things working.

QEMU has been recently split into sub-components and as a one-time operation to avoid breakage of tools, we are setting the QEMU sub-component of this BZ to "General". Please review and change the sub-component if necessary the next time you review this BZ. Thanks

The issue still exists on 8.3-av. 
(In reply to ybendito from comment #10)
> According to Microsoft feedback: 
> "the issue initially reported is in effect by a bug that affect Windows 2016
> (it was solved in Windows 2019 in the KB4482887) that needs to be solved as
> soon as possible. According my notes from the develop team the solution for
> this bug is planned to be published with the last hotfix KB next month of
> August"
> So, we will put this on hold till August and will check it with next
> cumulative update of 2016.

Hi Yuri, 

Seems KB4482887 is only provided for windows 10 and 2019 according to [1]. Would you please double check if they will fix windows 2016? Thanks.


[1] https://www.catalog.update.microsoft.com/Search.aspx?q=KB4482887

After evaluating this issue, there are no plans to address it further or fix it in an upcoming release.  Therefore, it is being closed.  If plans change such that this issue will be fixed in an upcoming release, then the bug can be reopened.

As we cannot force MS to release a hotfix for Windows Server 2016, closing based on comment 18.

Also hit this issue with -m 14336 (mem>4G) on win2016 guest vm.

1. Boot win2016 with qemu commands:
MALLOC_PERTURB_=1  /usr/libexec/qemu-kvm \
    -name 'avocado-vt-vm1'  \
    -sandbox on  \
    -machine pc  \
    -nodefaults \
    -device VGA,bus=pci.0,addr=0x2 \
    -m 14336  \
    -smp 2,maxcpus=4,cores=2,threads=1,dies=1,sockets=2  \
    -cpu 'Skylake-Server',hv_stimer,hv_synic,hv_vpindex,hv_relaxed,hv_spinlocks=0xfff,hv_vapic,hv_time,hv_frequencies,hv_runtime,hv_tlbflush,hv_reenlightenment,hv_stimer_direct,hv_ipi,+kvm_pv_unhalt \
    -device pvpanic,ioport=0x505,id=idASHu6b \
    -device qemu-xhci,id=usb1,bus=pci.0,addr=0x3 \
    -device usb-tablet,id=usb-tablet1,bus=usb1.0,port=1 \
    -device virtio-scsi-pci,id=virtio_scsi_pci0,num_queues=4,bus=pci.0,addr=0x4 \
    -blockdev node-name=file_image1,driver=file,auto-read-only=on,discard=unmap,aio=threads,filename=/home/kvm_autotest_root/images/win2016-64-virtio-scsi.qcow2,cache.direct=on,cache.no-flush=off \
    -blockdev node-name=drive_image1,driver=qcow2,read-only=off,cache.direct=on,cache.no-flush=off,file=file_image1 \
    -device scsi-hd,id=image1,drive=drive_image1,write-cache=on \
    -device virtio-net-pci,mac=9a:cf:62:20:54:41,id=ida7fdGT,netdev=idsWmwuh,bus=pci.0,addr=0x5  \
    -netdev tap,id=idsWmwuh,vhost=on \
    -blockdev node-name=file_cd1,driver=file,auto-read-only=on,discard=unmap,aio=threads,filename=/home/kvm_autotest_root/iso/windows/winutils.iso,cache.direct=on,cache.no-flush=off \
    -blockdev node-name=drive_cd1,driver=raw,read-only=on,cache.direct=on,cache.no-flush=off,file=file_cd1 \
    -device scsi-cd,id=cd1,drive=drive_cd1,write-cache=on  \
    -vnc :0  \
    -rtc base=localtime,clock=host,driftfix=slew  \
    -boot menu=off,order=cdn,once=c,strict=off \
    -qmp tcp:0:4445,server,nowait \
    -enable-kvm \
    -monitor stdio

2. {'execute': 'qmp_capabilities', 'id': 'i7jIHH13'}
{"return": {}, "id": "i7jIHH13"}
{'execute': 'device_add', 'arguments': {'id':'vcpu1','driver': 'Skylake-Server-x86_64-cpu', 'socket-id':1, 'die-id': 0, 'core-id':0, 'thread-id':0},'id': 'UBjvk5E2'}
{"return": {}, "id": "UBjvk5E2"}
{"timestamp": {"seconds": 1610025648, "microseconds": 249453}, "event": "RESET", "data": {"guest": true, "reason": "guest-reset"}}
{"timestamp": {"seconds": 1610025648, "microseconds": 262512}, "event": "RESET", "data": {"guest": true, "reason": "guest-reset"}}
{"timestamp": {"seconds": 1610025663, "microseconds": 181241}, "event": "RTC_CHANGE", "data": {"offset": 30512}}
{"timestamp": {"seconds": 1610025663, "microseconds": 181566}, "event": "RTC_CHANGE", "data": {"offset": 42932}}

3. Check the guest vm, guest reset immediately after hot added a cpu.

used versions:
kernel-4.18.0-240.5.1.el8_3.x86_64
qemu-kvm-5.1.0-15.module+el8.3.1+8772+a3fdeccd.x86_64
virtio-win-1.9.15-0.el8
seabios-1.14.0-1.module+el8.3.0+7638+07cf13d2.x86_64

Best Regards~
Peixiu

Hi Yuri, 

Would you please have a look at comment 22? The guest memory is more than 4G, is it the same issue in windows 2016? Thanks!

Peixiu, do you have the VM fully updated?

(In reply to ybendito from comment #24)
> Peixiu, do you have the VM fully updated?

Hi Yuri,

Sorry for late reply, for comment#22 result, did not with fully updates.
I tried to check latest updates and installed them today, There were 3 updates installed, KB4593226, KB4576750, KB4049065, rerun this job, guest vm hang after the cpu hotplugged.

Thanks~
Peixiu

qemu command line as:
/usr/libexec/qemu-kvm \
    -S  \
    -name 'avocado-vt-vm1'  \
    -sandbox on  \
    -machine pc  \
    -nodefaults \
    -device VGA,bus=pci.0,addr=0x2 \
    -m 14336  \
    -smp 2,maxcpus=4,cores=2,threads=1,dies=1,sockets=2  \
    -cpu 'Skylake-Server',hv_stimer,hv_synic,hv_vpindex,hv_relaxed,hv_spinlocks=0xfff,hv_vapic,hv_time,hv_frequencies,hv_runtime,hv_tlbflush,hv_reenlightenment,hv_stimer_direct,hv_ipi,+kvm_pv_unhalt \
    -chardev socket,nowait,path=/tmp/avocado_vjgk4b08/monitor-qmpmonitor1-20210112-090715-W7219jUP,id=qmp_id_qmpmonitor1,server  \
    -mon chardev=qmp_id_qmpmonitor1,mode=control \
    -chardev socket,nowait,path=/tmp/avocado_vjgk4b08/monitor-catch_monitor-20210112-090715-W7219jUP,id=qmp_id_catch_monitor,server  \
    -mon chardev=qmp_id_catch_monitor,mode=control \
    -device pvpanic,ioport=0x505,id=idMxL9VE \
    -chardev socket,nowait,path=/tmp/avocado_vjgk4b08/serial-serial0-20210112-090715-W7219jUP,id=chardev_serial0,server \
    -device isa-serial,id=serial0,chardev=chardev_serial0  \
    -chardev socket,id=seabioslog_id_20210112-090715-W7219jUP,path=/tmp/avocado_vjgk4b08/seabios-20210112-090715-W7219jUP,server,nowait \
    -device isa-debugcon,chardev=seabioslog_id_20210112-090715-W7219jUP,iobase=0x402 \
    -device qemu-xhci,id=usb1,bus=pci.0,addr=0x3 \
    -device usb-tablet,id=usb-tablet1,bus=usb1.0,port=1 \
    -device virtio-scsi-pci,id=virtio_scsi_pci0,num_queues=4,bus=pci.0,addr=0x4 \
    -blockdev node-name=file_image1,driver=file,auto-read-only=on,discard=unmap,aio=threads,filename=/home/kvm_autotest_root/images/win2016-64-virtio-scsi.qcow2,cache.direct=on,cache.no-flush=off \
    -blockdev node-name=drive_image1,driver=qcow2,read-only=off,cache.direct=on,cache.no-flush=off,file=file_image1 \
    -device scsi-hd,id=image1,drive=drive_image1,write-cache=on \
    -device virtio-net-pci,mac=9a:3b:a1:89:70:38,id=idckNDqD,netdev=idZlnS4u,bus=pci.0,addr=0x5  \
    -netdev tap,id=idZlnS4u,vhost=on,vhostfd=20,fd=14 \
    -blockdev node-name=file_cd1,driver=file,auto-read-only=on,discard=unmap,aio=threads,filename=/home/kvm_autotest_root/iso/windows/winutils.iso,cache.direct=on,cache.no-flush=off \
    -blockdev node-name=drive_cd1,driver=raw,read-only=on,cache.direct=on,cache.no-flush=off,file=file_cd1 \
    -device scsi-cd,id=cd1,drive=drive_cd1,write-cache=on  \
    -vnc :1  \
    -rtc base=localtime,clock=host,driftfix=slew  \
    -boot menu=off,order=cdn,once=c,strict=off \
    -enable-kvm

Please open a BZ for that. This BZ is for hotplug with small memory size.
For new BZ please specify the qemu version, we'll need to check whether this is a regression of qemu or not.
Probably such test was done in the past for 2016.

(In reply to ybendito from comment #27)
> Please open a BZ for that. This BZ is for hotplug with small memory size.
> For new BZ please specify the qemu version, we'll need to check whether this
> is a regression of qemu or not.
> Probably such test was done in the past for 2016.

Ok, filed a new Bug 1915715        - Windows 2016 guest will reboot/hang/quit after hot plug a vcpu with large memory

Thanks a lot~
Peixiu