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

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Date:	Thu, 18 Sep 2008 14:07:03 +0400
From:	Michael Tokarev <mjt@....msk.ru>
To:	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

PARAVIRT it is, not PARAVIRT_GUEST.

> 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.

Two more Asus motherboards expose exactly the same problem.

M3A-H/HDMI - AMD 780G/SB700, and
M2N-VM - nVidia MCP67 /  GeForce 7050

And from the above, 3 more:

M2NPV-VM - nVidia GeForce 6150/nForce 430
M3A78-EM - AMD780G/SB700
M2N-SLI DELUXE - nVidia MCP55 (unconfirmed)

With new BIOSes and with CONFIG_PARAVIRT enabled in kernel,
system does not boot.  It seems the stalls happens at more
or less random places, but the place is always the same on
the same motherboard and different kernels -- f.e. my
M3A78-EM always stops after "SLUB: " line as shown above,
be it 32- or 64bits kernel, 2.6.26 or 2.6.26.5.

> Any hints on this? ;)
> 
> Thanks!
> 
> /mjt

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