linux-kernel - Re: [x86, smap] general protection fault: fff2 [#1] PREEMPT DEBUG

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Date:	Tue, 15 Apr 2014 19:05:22 -0700
From:	"H. Peter Anvin" <hpa@...ux.intel.com>
To:	Jet Chen <jet.chen@...el.com>
CC:	LKML <linux-kernel@...r.kernel.org>,
	Fengguang Wu <fengguang.wu@...el.com>
Subject: Re: [x86, smap]  general protection fault: fff2 [#1] PREEMPT DEBUG_PAGEALLOC

On 04/10/2014 10:27 PM, Jet Chen wrote:
> [  371.380921] general protection fault: fff2 [#1] PREEMPT DEBUG_PAGEALLOC

I am guessing this is an issue with DEBUG_PAGEALLOC... this message is
odd in the extreme because it is hard to see how we could #GP(0xfff2)
here -- which normally would indicate having attempted to load 0xfff2 as
a segment selector (which is going to fail spectacularly).

This happens immediately after a popfq which enables interrupts(!), so
my guess is that we're trying to deliver an interrupt but that for some
reason there is garbage in the IDT or similar.

Unfortunately the GPF message doesn't include the IDT/GDT information...

	-hpa

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