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Bug 2156523

Summary: For disk hot-plug, RAWIO is not set actually
Product: Red Hat Enterprise Linux 9 Reporter: Han Han <hhan>
Component: libvirtAssignee: Virtualization Maintenance <virt-maint>
libvirt sub component: General QA Contact: Han Han <hhan>
Status: CLOSED MIGRATED Docs Contact:
Severity: low    
Priority: low CC: jsuchane, lmen, mprivozn, virt-maint, yisun
Version: 9.2Keywords: MigratedToJIRA, Triaged
Target Milestone: rcFlags: pm-rhel: mirror+
Target Release: ---   
Hardware: Unspecified   
OS: Unspecified   
Whiteboard:
Fixed In Version: Doc Type: If docs needed, set a value
Doc Text:
Story Points: ---
Clone Of: Environment:
Last Closed: 2023-07-07 21:19:27 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:

Description Han Han 2022-12-27 09:34:37 UTC 
Description of problem:
As subject

Version-Release number of selected component (if applicable):
qemu-kvm-7.2.0-2.el9.x86_64
kernel-5.14.0-207.el9.x86_64
libvirt-8.10.0-2.el9.x86_64

How reproducible:


Steps to Reproduce:
1. Start an VM
➜  ~ virsh list 
 Id   Name       State
--------------------------
 4    rhel-9.2   running


2. Attach an disk with rawio='yes' then check the capabilities of the qemu-kvm process and its threads
➜  ~ virsh attach-device rhel-9.2 ./rawio.xml         
Device attached successfully 

➜  ~ cat rawio.xml 
    <disk type='block' device='lun' rawio='yes'>
      <driver name='qemu' type='raw'/>
      <source dev='/dev/sda'/>
      <target dev='sda' bus='scsi'/>
      <address type='drive' controller='0' bus='0' target='0' unit='0'/>
    </disk>


➜  ~ getpcaps `pidof qemu-kvm`
439898: =

➜  ~ for i in $(ps -T -p `pidof qemu-kvm`|awk 'NR!=1{print $2}');do getpcaps $i;done
439898: =
439917: =
439921: =
439922: =
439924: =

Actual results:
As above

Expected results:
- Disallow hot-plug with rawio='yes'
- Or support to set/unset the RAWIO capabilities for qemu-kvm process or its threads. Expect the results like starting VM with rawio='yes':
➜  ~ getpcaps `pidof qemu-kvm`                                                     
440300: cap_sys_rawio=eip

➜  ~ for i in $(ps -T -p `pidof qemu-kvm`|awk 'NR!=1{print $2}');do getpcaps $i;done
440300: cap_sys_rawio=eip
440315: cap_sys_rawio=eip
440319: cap_sys_rawio=eip
440320: cap_sys_rawio=eip
440323: cap_sys_rawio=eip

Additional info:
Comment 1 Han Han 2022-12-27 09:44:26 UTC 
The same issue for hostdev@rawio:
  <hostdev mode='subsystem' type='scsi' rawio='yes'>
    <source>
      <adapter name='scsi_host2'/>
      <address bus='0' target='0' unit='0'/>
    </source>
    <readonly/>
  </hostdev>
Comment 2 Michal Privoznik 2023-01-18 12:09:27 UTC 
I'm not sure this is a solvable issue. I mean, once QEMU permissions are dropped there's not a mechanism that would allow us to enable it in QEMU again. It would require us to not drop CAP_SYS_RAWIO from the bounding set and then notify QEMU to try and promote the capability. But yeah, QEMU knows nothing about its capabilities. In other words, we may as well deny hotplugging if QEMU was started without the capability.