linux-kernel - Re: [Bisected] 3.7-rc1 can't resume (still present in 3.9)

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Message-ID: <51DDC972.3010005@student.kit.edu>
Date:	Wed, 10 Jul 2013 22:52:02 +0200
From:	Christian Sünkenberg 
	<christian.suenkenberg@...dent.kit.edu>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	Jonas Heinrich <onny@...ject-insanity.org>,
	"len.brown@...el.com" <len.brown@...el.com>,
	"pavel@....cz" <pavel@....cz>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"x86@...nel.org" <x86@...nel.org>, "rjw@...k.pl" <rjw@...k.pl>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>
Subject: Re: [Bisected] 3.7-rc1 can't resume (still present in 3.9)

Hello,

On 05/01/2013 07:33 PM, H. Peter Anvin wrote:
> On 05/01/2013 10:01 AM, Jonas Heinrich wrote:
>> Hello, I tried the newest kernel, 3.9 today but the bug is still
>> present. Applying the attached patch solves the bug for me.
>>
>> Best regards, Jonas Heinrich
> 
> Okay... WTF is going on here?  Does pmode_behavior just not get set up
> correctly?  Since it seems you can get it to wake up with your patch,
> perhaps we can get read out the value of pmode_behavior and print it...

indeed, arch/x86/kernel/acpi/sleep.c tries an rdmsr_safe(MSR_EFER, ...)
and sets WAKEUP_BEHAVIOR_RESTORE_EFER bit on success, however,
on 90 nm Pentium M (Family 6, Model 13), reading an invalid MSR
is not guaranteed to trap, see Erratum X4 in "Intel® Pentium® M
Processor on 90 nm Process with 2-MB L2 Cache and Intel® Processor A100
and A110 on 90 nm process with 512-KB L2 Cache Specification Update".
On Jonas' T43, which has an affected Pentium M without EFER,
rdmsr_safe(MSR_EFER, ...) succeeds and WAKEUP_BEHAVIOR_RESTORE_EFER
gets set, while on resume the corresponding wrmsr traps and thus resume
fails.

The pre-3.7 code snippet incidentally catched this by not restoring
EFER when it would be restored to all 0s.

HTH,
Christian

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