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

[ebiederm@xmission.com (Eric W. Biederman)]

Simon Horman <horms@verge.net.au> writes:

> [ Added Andrew Morton, Eric Biederman, Vivek Goyal and Haren Myneni to CC ]
>
> On Thu, Oct 23, 2008 at 05:41:29PM -0200, Eduardo Habkost wrote:
>> On Thu, Oct 23, 2008 at 10:28:24AM +1100, Simon Horman wrote:
>> > On Mon, Oct 20, 2008 at 01:01:32PM -0200, Eduardo Habkost wrote:
>> > > The following two patches should make kdump work when the kvm-intel module
>> > > is loaded. We need to disable vmx mode before booting the kdump kernel,
>> > > so I've introduced a notifier interface where KVM can hook and disable
>> > > virtualization on all CPUs just before they are halted.
>> > > 
>> > > It has the same purpose of the KVM reboot notifier that gets executed
>> > > at kexec-time. But on the kdump case, things are not as simple because
>> > > the kernel has just crashed.
>> > > 
>> > > The notifier interface being introduced is x86-specific. I don't know
>> > > if an arch-independent interface would be more appropriate for this
>> > > case.

My preference would be to have a magic function call that compiles out when
kvm isn't present.  This is a code path that is hard to audit and test, and
get right.  A notifier chain seems to make a proper audit all but impossible.

Why do we need to disable vmx mode before booting a normal linux kernel?
Is it possible to disable vmx mode before we enable interrrupts in the
kdump kernel?

Eric

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