RE: General KVM/QEMU VM debugging techniques

RE: General KVM/QEMU VM debugging techniques

[Kallol Biswas [C]]

Hi,
    We are observing a problem with CPU hotplug.

If secureboot option is enabled under UEFI  and then if we try to do CPU hotplug the VM crashes/just reboots.

No crash dump is generated, no panic message, just VM restarts. Issue seems like: 
https://bugzilla.redhat.com/show_bug.cgi?id=1834250

What are the debugging techniques we can apply to halt the VM and examine what's going on?
VM has been configured with crash dump.


Nucleodyne at Nutanix
408-718-8164

Re: General KVM/QEMU VM debugging techniques

[Igor Mammedov]

On Fri, 1 Apr 2022 23:50:16 +0000
"Kallol Biswas [C]" <kallol.biswas@nutanix.com> wrote:

> Hi,
>     We are observing a problem with CPU hotplug.
> 
> If secureboot option is enabled under UEFI  and then if we try to do CPU hotplug the VM crashes/just reboots.
> 
> No crash dump is generated, no panic message, just VM restarts. Issue seems like: 
> https://bugzilla.redhat.com/show_bug.cgi?id=1834250

CPU hotplug with SMM (for q35) was merged in QEMU-5.2
and unplug part in 6.0, you also need a matching OVMF build
to make it work. Later upto 6.2 (included) there were minor
fixes dealing with incorrect configs.

> What are the debugging techniques we can apply to halt the VM and examine what's going on?
> VM has been configured with crash dump.

I'd start with https://www.linux-kvm.org/page/Tracing

to find out when it goes south.

> Nucleodyne at Nutanix
> 408-718-8164
> 

Re: General KVM/QEMU VM debugging techniques

[Laszlo Ersek]

On 04/04/22 14:36, Igor Mammedov wrote:
> On Fri, 1 Apr 2022 23:50:16 +0000
> "Kallol Biswas [C]" <kallol.biswas@nutanix.com> wrote:
> 
>> Hi,
>>     We are observing a problem with CPU hotplug.
>>
>> If secureboot option is enabled under UEFI  and then if we try to do CPU hotplug the VM crashes/just reboots.
>>
>> No crash dump is generated, no panic message, just VM restarts. Issue seems like: 
>> https://bugzilla.redhat.com/show_bug.cgi?id=1834250
> 
> CPU hotplug with SMM (for q35) was merged in QEMU-5.2
> and unplug part in 6.0, you also need a matching OVMF build
> to make it work. Later upto 6.2 (included) there were minor
> fixes dealing with incorrect configs.
> 
>> What are the debugging techniques we can apply to halt the VM and examine what's going on?
>> VM has been configured with crash dump.
> 
> I'd start with https://www.linux-kvm.org/page/Tracing
> 
> to find out when it goes south.
> 
>> Nucleodyne at Nutanix
>> 408-718-8164
>>
> 

Also don't forget to build OVMF with DEBUG_VERBOSE (set
gEfiMdePkgTokenSpaceGuid.PcdDebugPrintErrorLevel to 0x8040004F), and to
capture the OVMF debug log (-debugcon file:debug.log -global
isa-debugcon.iobase=0x402).

Laszlo