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-ma	Assignee:	Cornelia Huck <cohuck>
Status:	CLOSED CANTFIX	QA Contact:	Min Deng <mdeng>
Severity:	medium	Docs Contact:
Priority:	high
Version:	7.6-Alt	CC:	cohuck, ddepaula, juzhang, michen, mrezanin, mtessun, ngu, qzhang, thuth, toneata
Target Milestone:	rc	Keywords:	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:
Clones:	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.