linux-kernel - Re: [Regression] "x86-64/efi: Use EFI to deal with platform wall clock" prevents my machine from booting

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Date:	Mon, 06 Aug 2012 07:44:34 +0100
From:	"Jan Beulich" <JBeulich@...e.com>
To:	<cJ-ko@...gloub.eu>, "H. Peter Anvin" <hpa@...or.com>
Cc:	"Ingo Molnar" <mingo@...nel.org>,
	"Matt Fleming" <matt.fleming@...ux.intel.com>,
	<linux-efi@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [Regression] "x86-64/efi: Use EFI to deal with platform
 wall clock" prevents my machine from booting

>>> On 06.08.12 at 00:28, "H. Peter Anvin" <hpa@...or.com> wrote:
> On 08/05/2012 02:29 PM, Jérôme Carretero wrote:
>> Hi,
>>
>> My PC (AMD Bulldozer + Asus SABERTOOTH 990FX) booted fine from UEFI
>> and it broke between v3.5 and v3.6-rc1.
>> Other machines with old BIOSes booted fine so I looked into EFI-related
>> patches trying to revert them, because I didn't know what else to do.
>>
>> Bingo, bacef661: x86-64/efi: Use EFI to deal with platform wall clock.
>>
>> At the moment I reverted this commit after v3.6-rc1-133-g42a579a,
>> and it boots fine.
>>
>> This really not my domain so tell me if I can help testing.
>>
> 
> Thank you... we were aware of the problem but had not been able to 
> reproduce it, so we had hoped someone would bisect or otherwise identify 
> the faulty patch.

Faulty? Without technical detail I'd be careful with this, as there's
too many broken EFI implementation around.

The only change that has a (very low) potential for causing
problems by itself is the earlier calling of efi_enter_virtual_mode(),
which was requested/recommended by Matthew.

I am e.g. (meanwhile) aware of (Intel) systems that use floating
point instructions in the UEFI runtime code, which is clearly a
violation of the spec; having the kernel continue to be not spec
compliant is a questionable tradeoff.

In any case, without having seen _how_ things break I don't
think a decision should be taken if/how to address this
(apparent) regression.

Jan
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