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Bug 1650580

Summary: Trying to start a guest with hugetlbfs backing does not bail out so providing saying that hugetlbfs is not supported before actually trying to start the guest.
Product: Red Hat Enterprise Linux 7 Reporter: David Hildenbrand <dhildenb>
Component: qemu-kvm-maAssignee: Cornelia Huck <cohuck>
Status: CLOSED CANTFIX QA Contact: Min Deng <mdeng>
Severity: medium Docs Contact:
Priority: high    
Version: 7.6-AltCC: cohuck, ddepaula, juzhang, michen, mrezanin, mtessun, ngu, qzhang, thuth, toneata
Target Milestone: rcKeywords: ZStream
Target Release: ---   
Hardware: s390x   
OS: Linux   
Whiteboard:
Fixed In Version: Doc Type: If docs needed, set a value
Doc Text:
Story Points: ---
Clone Of:
: 1672919 (view as bug list) Environment:
Last Closed: 2019-02-06 11:20:48 UTC Type: Bug
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:
Bug Depends On:    
Bug Blocks: 1672919    

Description David Hildenbrand 2018-11-16 14:22:22 UTC 
Description of problem:

Hugetlbfs is not supported for s390x KVM guests in 7.6-alt - and doesn't work.
However, it will not bail out, instead the guest will try to start and eventually fail/crash when running.

This is problematic: E.g. starting a KVM guest with hugetlbfs under RHEL 8 (which works and is supported) and migrating it to 7.6-alt will not properly
fail during migration and not fallback to the source side. Instead, the guest will crash after migration, essentially resulting in data loss.

How reproducible: 100%

Steps to Reproduce:
1. Try to start a guest with hugetlbfs backing

Actual results: Guest will fail to run without a proper error message.

Expected results: QEMU will properly bail out, saying that hugetlbfs is not supported before actually trying to start the guest.
Comment 3 Min Deng 2018-11-22 03:13:17 UTC 
Reproduced the bug on the following builds
kernel-4.14.0-115.el7a.s390x
qemu-kvm-ma-2.12.0-18.el7.s390x
Steps,
*Enabled Huge page on host beforehand
1.mount -t hugetlbfs none /mnt/kvm_hugepage
2.echo 1024 > /proc/sys/vm/nr_hugepages 
3.boot up a guest with huge page 
/usr/libexec/qemu-kvm -name avocado-vt-vm1 -sandbox off -machine s390-ccw-virtio -nodefaults -vga none -chardev socket,id=qmp_id_qmpmonitor1,path=/tmp/1,server,nowait -mon chardev=qmp_id_qmpmonitor1,mode=control -chardev socket,id=qmp_id_catch_monitor,path=/tmp/2,server,nowait -mon chardev=qmp_id_catch_monitor,mode=control -chardev socket,id=serial_id_serial0,path=/tmp/3,server,nowait -device sclpconsole,chardev=serial_id_serial0 -device virtio-scsi-ccw,id=virtio_scsi_ccw0 -drive id=drive_image1,if=none,snapshot=off,aio=threads,cache=none,format=qcow2,file=rhel76-s390x-virtio-scsi.qcow2 -device scsi-hd,id=image1,drive=drive_image1 -m 1024 -mem-path /mnt/kvm_hugepage -smp 4,maxcpus=4,cores=2,threads=1,sockets=2 -cpu host -nographic -rtc base=utc,clock=host,driftfix=slew -boot strict=on -no-shutdown -enable-kvm -monitor stdio

Actual results,
(qemu) qemu-kvm: warning: CMM will not be enabled because it is not compatible with hugetlbfs.
error: kvm run failed Bad address
PSW=mask 0000000180000000 addr 000000003fe006e0 cc 00
R00=0000000000000000 R01=0000000000000000 R02=0000000000000000 R03=0000000000000000
R04=0000000000000000 R05=0000000000000000 R06=0000000000000000 R07=0000000000000000
R08=0000000000000000 R09=0000000000000000 R10=0000000000000000 R11=0000000000000000
R12=0000000000000000 R13=0000000000000000 R14=0000000000000000 R15=0000000000000000
F00=0000000000000000 F01=0000000000000000 F02=0000000000000000 F03=0000000000000000
F04=0000000000000000 F05=0000000000000000 F06=0000000000000000 F07=0000000000000000
F08=0000000000000000 F09=0000000000000000 F10=0000000000000000 F11=0000000000000000
F12=0000000000000000 F13=0000000000000000 F14=0000000000000000 F15=0000000000000000
V00=00000000000000000000000000000000 V01=00000000000000000000000000000000
V02=00000000000000000000000000000000 V03=00000000000000000000000000000000
V04=00000000000000000000000000000000 V05=00000000000000000000000000000000
V06=00000000000000000000000000000000 V07=00000000000000000000000000000000
V08=00000000000000000000000000000000 V09=00000000000000000000000000000000
V10=00000000000000000000000000000000 V11=00000000000000000000000000000000
V12=00000000000000000000000000000000 V13=00000000000000000000000000000000
V14=00000000000000000000000000000000 V15=00000000000000000000000000000000
V16=00000000000000000000000000000000 V17=00000000000000000000000000000000
V18=00000000000000000000000000000000 V19=00000000000000000000000000000000
V20=00000000000000000000000000000000 V21=00000000000000000000000000000000
V22=00000000000000000000000000000000 V23=00000000000000000000000000000000
V24=00000000000000000000000000000000 V25=00000000000000000000000000000000
V26=00000000000000000000000000000000 V27=00000000000000000000000000000000
V28=00000000000000000000000000000000 V29=00000000000000000000000000000000
V30=00000000000000000000000000000000 V31=00000000000000000000000000000000
C00=00000000000000e0 C01=0000000000000000 C02=0000000000000000 C03=0000000000000000
C04=0000000000000000 C05=0000000000000000 C06=0000000000000000 C07=0000000000000000
C08=0000000000000000 C09=0000000000000000 C10=0000000000000000 C11=0000000000000000
C12=0000000000000000 C13=0000000000000000 C14=00000000c2000000 C15=0000000000000000

Expected results,
QEMU will properly bail out, saying that hugetlbfs is not supported before actually trying to start the guest.