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SubjectRe: [PATCH v4] enable x2APIC without interrupt remapping under KVM
On Tue, Jun 30, 2009 at 11:43:41AM -0700, Yinghai Lu wrote:
> 2009/6/30 Gleb Natapov <>:
> >>
> >> how about kexec second kernel in KVM ?
> >>
> >> x2apic_preenabled will be set in second kernel.
> >>
> > Yes, bummer. But the similar problem exist now and without KVM. After
> > running x2apic enabled kernel you can't kexec kernel without x2apic
> > support.
> if the first kernel enable x2apic and intr_remapping, and second
> kernel has x2apic and intr_remap support.
> we can kexec the second kernel.
And if it hasn't we cannot, that is what I am trying to point out.

> restoring to original state is not possible for kdump case.
Shouldn't it be enough to run UP kernel for kdump? So kdump can reset BSP
apic to xAPIC mode before starting a kernel with maxcpus=1.

> maybe with minor change to your patch, you could kexec the in kexec
> second kernel with x2apic support.
My patch can easily avoid the issue by checking max_physical_apicid > 255
instead of x2apic_preenabled.


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