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SubjectRe: [tip:x86/debug] x86/kdump: No need to disable ioapic/ lapic in crash path
From: Fernando Luis Vázquez Cao <>
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<> 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;
* 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


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