linux-kernel - Re: PARAVIRT_GUEST bug? [was: Stable regression: usb-storage is stuck in 2.6.26.5]

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Date:	Tue, 16 Sep 2008 10:19:08 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Michael Tokarev <mjt@....msk.ru>
CC:	linux-kernel@...r.kernel.org
Subject: Re: PARAVIRT_GUEST bug? [was: Stable regression: usb-storage is stuck
 in 2.6.26.5]

Michael Tokarev wrote:
> Michael Tokarev wrote:
>
> [usb-storage hangs on asus M2NPV-VM (nVidia GeForce 6150/nForce 430)
>  motherboard with latest bios]
>
>> Ok, it turned out to be pretty.. interesting.
>>
>> It's not a regression within -stable kernel series.  The problem
>> happens when BOTH are true:
>>
>>   - using latest BIOS for this mobo (1401), AND
>>   - enabling KVM_GUEST in kernel.
>>
>> The only difference in my kernel config between .1 and .5 was
>> to enable KVM_GUEST and KVM_CLOCK, and also I2C_HELPER_AUTO
>> which was added by kernel update.
>>
>> Going with previous BIOS (1201) OR disabling PARAVIRT_GUEST
>> fixes the problem.  I'll try to figure out which config
>> option is at problem here.
>
> After seeing similar situation on another motherboard, I
> become curious.
>
> Here's the result:  M3A78-EM motherboard (also from Asus),
> AMD780G/SB700 etc.  Updating to one of the latest bios
> makes the system unbootable.  Kernel hangs on boot right
> after displaying
>
>  SLUB: Genslabs=12, HWalign=64, Order=0-1, MinObjects=4, CPUs=2, Nodes=1
>
> Reverting to the older BIOS or disabling PARAVIRT_GUEST in kernel
> fixes this (turning off KVM_GUEST isn't enough), and kernel happily
> boots further, with next line being
>
>  hpet clockevent registered
>  ...
>
> Reportedly, another Asus motherboard (M2N-SLI DELUXE) also hangs
> with new BIOS and KVM_GUEST optimizations turned on, but not on
> older BIOS.
>
> So it's quite.. funny.  At least SOME latest BIOSes from Asustec,
> together with PARAVIRT_GUEST, -- a problem.  Don't do either of
> those, and it's all ok.
>
> The question is if Asus introduced the same bug in quite.. some
> of their recent BIOSes, or PARAVIRT_GUEST code is somehow buggy
> and the bug is exposed by new BIOS code.
>
> Any hints on this? ;)

PARAVIRT_GUEST doesn't enable anything by itself; it just makes other
config options appear.  What other config options are you enabling?

That is, what's the diff between a working and a non-working .config?

    J
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