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

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Message-ID: <20130925131230.GL21381@console-pimps.org>
Date:	Wed, 25 Sep 2013 14:12:30 +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 Mon, 23 Sep, at 11:45:28AM, 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.
> 
> This patch disables the interrupt flag, while leaving the existing IDT
> in place. The CPU won't care about the IDT at all as long as the
> interrupt bit is off, so it's safe to leave it in place as nothing will
> ever happen to it.
> 
> Signed-off-by: Bart Kuivenhoven <bemk@...hat.com>
> ---
>  arch/x86/boot/compressed/eboot.c | 15 +--------------
>  1 file changed, 1 insertion(+), 14 deletions(-)

Applied, thanks Bart!

-- 
Matt Fleming, Intel Open Source Technology Center
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