linux-kernel - Re: Geode LX boot fails after x86 microcode revision change

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Date:	Tue, 22 Nov 2011 14:00:48 +0100
From:	Borislav Petkov <bp@...64.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Borislav Petkov <bp@...64.org>, Daniel Drake <dsd@...top.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Geode LX boot fails after x86 microcode revision change

On Tue, Nov 08, 2011 at 02:19:29PM -0800, H. Peter Anvin wrote:
> > If so, then a family check is unavoidable.
> 
> Either that, or make changes so that we can handle exceptions earlier.
> That would be useful for other reasons.

Well, I did some experimenting with this by forcing a guest to #GP on a
rdmsr in kvm. What I got was the early_idt_handler's panic message:

"PANIC: early exception %02lx rip %lx:%lx error %lx cr2 %lx\n"

because of the following boot code flow:

x86_64_start_kernel
|-> ... set_intr_gate           /* register early_idt_handler */
|-> x86_64_start_reservations
    |-> start_kernel
        |-> setup_arch
        |-> early_cpu_init()    /*
				 * this is where we need the extable for
				 * rdmsr_safe
				 */
...
    |-> trap_init()             /* switch to default #GP handler */

and do_general_protection does the actual exception fixup. Now, the
whole setup_arch() is running with the initial traps and only after we
finish it and a bunch of other stuff, we switch to the #GP handler in
trap_init().

>From where I stand, maybe I could try to teach the early_idt_handler in
head_64.S to do fixup_exception() ?

Also, we might need the patches which sort extable at build time too,
which are floating around lkml currently.

Hmm...

-- 
Regards/Gruss,
Boris.

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