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    Date
    SubjectRe: [tip:x86/debug] x86/kdump: No need to disable ioapic/ lapic in crash path
    From
    From: Fernando Luis Vázquez Cao <fernando@oss.ntt.co.jp>
    Subject: Re: [tip:x86/debug] x86/kdump: No need to disable ioapic/ lapic in crash path
    Date: Wed, 07 Mar 2012 19:53:16 +0900

    > On 03/01/2012 08:19 AM, Eric W. Biederman wrote:
    >
    >> Don Zickus<dzickus@redhat.com> writes:
    >>> It probably is, except I never hacked on idt code before and my
    >>> assembly
    >>> isn't that good. I have been trying to find examples to copy from to
    >>> give
    >>> it a try. So far I was using early_idt_handlers with early_printk to
    >>> see
    >>> if I could capture some printk messages while jumping from the first
    >>> kernel to the second kernel (when the other early_idt_handlers would
    >>> kick
    >>> in for the second kernel).
    >>>
    >>> Tips? Better examples?
    >> That is a particularly good example. When I took a quick look earlier
    >> that is the first place we reload the idt in the kernel boot so that
    >> is
    >> one of two places that needs to be modified.
    >
    > Hi Eric, Don
    >
    > Sorry for chiming in so late.
    >
    > We run into the same NMI problems and wrote some patches that tackle
    > the kernel boot side of things. They have been extensively tested
    > using
    > qemu-kvm and things seem to be working as expected (after receiving an
    > early NMI the kernel continues without problem; after the iret there
    > is no
    > stack corruption or register corruption).
    >
    > I will be replying to this email with the patches.
    >

    Should the following also be fixed?

    /*
    * Do not allocate memory (or fail in any way) in machine_kexec().
    * We are past the point of no return, committed to rebooting now.
    */
    void machine_kexec(struct kimage *image)
    {
    unsigned long page_list[PAGES_NR];
    void *control_page;
    int save_ftrace_enabled;
    <cut>
    /*
    * The gdt & idt are now invalid.
    * If you want to load them you must set up your own idt & gdt.
    */
    set_gdt(phys_to_virt(0), 0);
    set_idt(phys_to_virt(0), 0); <--- This

    Thanks.
    HATAYAMA, Daisuke

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