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

["Cédric Le Goater" <clg@kaod.org>]

On 1/9/23 15:52, Janosch Frank wrote:
> 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.

aaahh. So "-machine confidential-guest-support=pv0 -object s390-pv-guest,id=pv0"
is equivalent to "-global virtio-device.iommu_platform=true". I should have
looked closer :/

Thanks for the clarification,

C.