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

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Date:	Sat, 13 Jul 2013 01:36:28 +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 07/11/2013 01:57 AM, H. Peter Anvin wrote:
> On 07/10/2013 01:52 PM, Christian Sünkenberg wrote:
>> 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.
>>
> 
> That does seem like a reasonable explanation.
> 
> Does this patch fix the problem?  (Comment blatantly ripped off from
> your email message.)

Jonas tried your patch and it fixes suspend/resume on his T43, although
IMHO the safest approach would be to just add an exception for
Vendor==Intel && Family==6 && Model==13, or more generally Vendor==Intel
&& !supports_long_mode, as the same erratum also warns about wrmsr
possibly not triggering a GP either.
Anyways, at least on this specific MSR with the Pentium M Jonas tested,
it behaved correctly on every try, so I'd say your patch does the trick,
thank you very much!

As a side note, I found a similar erratum #33 in "Pentium® Processor
Specification Update" for Intel P54C (Family 5, Model 2), which would,
supposed there are P54C systems with ACPI sleep/resume support, result
in MSR 0 (P5_MC_ADDR) to be saved and restored instead of nonexistent EFER.

Kind regards,
Christian


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