linux-kernel - Re: [tip:x86/debug] x86/kdump: No need to disable ioapic/ lapic in crash path

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Date:	Fri, 09 Mar 2012 09:59:02 +0900 (   )
From:	HATAYAMA Daisuke <d.hatayama@...fujitsu.com>
To:	fernando@....ntt.co.jp
Cc:	ebiederm@...ssion.com, dzickus@...hat.com,
	linux-tip-commits@...r.kernel.org, torvalds@...ux-foundation.org,
	kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
	mingo@...hat.com, tglx@...utronix.de, hpa@...or.com, mingo@...e.hu,
	yinghai@...nel.org, akpm@...ux-foundation.org, vgoyal@...hat.com
Subject: Re: [tip:x86/debug] x86/kdump: No need to disable ioapic/ lapic in
 crash path

From: Fernando Luis Vázquez Cao <fernando@....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@...hat.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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