Re: [PATCH v2 3/4] s390x/pv: Introduce a s390_pv_check() helper for runtime

[Janosch Frank <frankja@linux.ibm.com>]

On 1/9/23 15:31, Janosch Frank wrote:
> On 1/9/23 14:53, Cédric Le Goater wrote:
>> On 1/9/23 14:45, Janosch Frank wrote:
>>> On 1/9/23 14:30, Cédric Le Goater wrote:
>>>> On 1/9/23 10:49, Janosch Frank wrote:
>>>>> On 1/9/23 10:27, Cédric Le Goater wrote:
>>>>>> On 1/9/23 10:04, Janosch Frank wrote:
>>>>>>> On 1/6/23 08:53, Cédric Le Goater wrote:
>>>>>>>> From: Cédric Le Goater <clg@redhat.com>
>>>>>>>>
>>>>>>>> If a secure kernel is started in a non-protected VM, the OS will hang
>>>>>>>> during boot without giving a proper error message to the user.
>>>>>>>
>>>>>>> Most of the time you see nothing in the console because libvirt is too slow. If you start the VM in paused mode, attach a console and then resume it, then you'll see a nice error message.
>>>>>>
>>>>>> If you wait long enough, the VM fails to mount / and falls into the dracut
>>>>>> initrams.
>>>>>
>>>>> I have the feeling that we're not talking about the same thing here.>
>>>>      > A PV VM always starts out as a non-PV VM and is put into PV mode via two diag308 subcodes (8 & 10). ALL PV subcodes (8 - 10) are spec exceptions if the host isn't enabled for PV.
>>>>
>>>> The corner case this patch is trying to address is for a PV-enabled host,
>>>> a secure enabled OS and !PV-enabled QEMU.
>>>>
>>>> Please run this command on a secure disk image :
>>>>
>>>>       qemu-system-s390x -M s390-ccw-virtio -accel kvm -drive file=<file>,if=virtio,format=qcow2 -nographic -nodefaults -serial mon:stdio
>>>>
>>>> and tell me what you get.
>>>>
>>>
>>> qemu-system-s390x -M s390-ccw-virtio -accel kvm -drive file=u2204.qcow2,if=virtio,format=qcow2 -nographic -nodefaults -serial mon:stdio
>>> LOADPARM=[        ]
>>> Using virtio-blk.
>>> Using SCSI scheme.
>>> .............................................................................................................................
>>> Secure unpack facility is not available
>>
>> Yes. That's with a !PV-enabled host. Correct ?
>>
>> Can you try with prot_virt=1 on the host please ?
> 
> With prot_virt=1 it boots until it doesn't find the file system (at
> least if you give it a bit more memory than the standard 256MB):
> 
> qemu-system-s390x -M s390-ccw-virtio -accel kvm -drive
> file=u2204.qcow2,if=virtio,format=qcow2 -nographic -nodefaults -serial
> mon:stdio -m 4096
> [Linux boot stuff]
> ALERT!  /dev/disk/by-path/ccw-0.0.0000-part1 does not exist.  Dropping
> to a shell!
> 

I.e. it boots into secure mode just fine.

Now if you add iommu_platform=true to the device then it'll even boot 
from disk.

So we'd rather need an error message if you attach a device without the 
iommu being set to true. The whole topic of PV iommu problems has a few 
windings which I don't fully want to bring to electronic paper right now.

Either you start a secure guest that has devices with manual iommu 
entries or you go the launch security route and let libvirt/qemu handle 
it for you.