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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 <gleb@redhat.com>:
    >
    > >>
    > >> 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.

    --
    Gleb.


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