Re: [PATCH 0/2] kvm: disable virtualization on kdump

[Avi Kivity <avi@redhat.com>]

Eduardo Habkost wrote:
>> (we can use NMI IPIs, but that will likely be messy)
>>     
>
> NMI IPIs are already used on x86 native_machine_crash_shutdown(), so
> it wouldn't get more messy that it is currently. We just need to add
> another bit of code to the code that already runs on an NMI handler.
>
>   

That looks like the easiest (and best) way out.

> My question is: is a notifier chain too much complexity for a sensible
> piece of code like that? If so, a compile-time hook on that point
> would be safer,

I think an unconditional vmx disable is wanted here, so kexec can work 
with other hypervisors.

>  but then it wouldn't work when KVM is compiled as a
> out-of-tree module.
>   

The external module can do without.  It's possible to hijack the nmi 
vector, but I don't think that's a good idea.  If someone wants 
kexec+vmx on an older kernel, they can patch that kernel.

>> But what happens when the kdump kernel reboots?  If it is uniprocessor,  
>> it will never have a chance to disable vmx on other cpus.  Using acpi  
>> reset (now default) works around this on some machines, but not all.
>>     
> Good point. My problem was a hang when booting the kdump kernel, but it
> may also cause problems later, when the kdump kernel reboots.
>   

The hang was likely caused by vmx blocking INIT.  Sigh.

-- 
error compiling committee.c: too many arguments to function


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