linux-kernel - Re: [PATCH] x86 efi: bugfix interrupt disabling sequence

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Message-ID: <20130920152859.GC21381@console-pimps.org>
Date:	Fri, 20 Sep 2013 16:28:59 +0100
From:	Matt Fleming <matt@...sole-pimps.org>
To:	Bart Kuivenhoven <bemk@...hat.com>
Cc:	matt.fleming@...el.com, hpa@...or.com, tglx@...utronix.de,
	mingo@...hat.com, x86@...nel.org, linux-efi@...r.kernel.org,
	linux-kernel@...r.kernel.org, jcm@...hat.com, msalter@...hat.com
Subject: Re: [PATCH] x86 efi: bugfix interrupt disabling sequence

On Wed, 18 Sep, at 07:28:53PM, Bart Kuivenhoven wrote:
> The problem in efi_main was that the idt was cleared before the
> interrupts were disabled.
> 
> The UEFI spec states that interrupts aren't used so this shouldn't be
> too much of a problem. Peripherals however don't necessarily know about
> this and thus might cause interrupts to happen anyway. Even if
> ExitBootServices() has been called.
>
> This means there is a risk of an interrupt being triggered while the IDT
> register is nullified and the interrupt bit hasn't been cleared,
> allowing for a triple fault.

Just to be clear, you haven't witnessed a triple fault, correct?

> This patch fixes this by clearing the interrupt bit before the lidt
> instruction.

I think we can go even further than this and get rid of all of the IDT
code in the EFI boot stub. The kernel maintains its own IDT anyway.

-- 
Matt Fleming, Intel Open Source Technology Center
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