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Subject: Re: CONFIG_DEBUG_VIRTUAL breaks boot on x86-32
To:     William Kucharski <william.kucharski@oracle.com>,
        Meelis Roos <mroos@linux.ee>
CC:     LKML <linux-kernel@vger.kernel.org>, <linux-mm@kvack.org>
References: <4d5ee3b0-6d47-a8df-a6b3-54b0fba66ed7@linux.ee>
 <A1B7F481-4BF6-4441-8019-AE088F8A8939@oracle.com>
From:   Ralph Campbell <rcampbell@nvidia.com>
Message-ID: <f39477da-a1ef-e31e-a72d-8ea1d5755234@nvidia.com>
Date:   Tue, 26 Mar 2019 13:11:31 -0700
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On 3/26/19 6:52 AM, William Kucharski wrote:
> Does this still happen on 5.1-rc2?
> 
> Do you have idea as to what max_low_pfn() gets set to on your system at boot time?
> 
>  From the screen shot I'm guessing it MIGHT be 0x373fe, but it's hard to know for sure.
> 
> 
>> On Mar 21, 2019, at 2:22 PM, Meelis Roos <mroos@linux.ee> wrote:
>>
>> I tried to debug another problem and turned on most debug options for memory.
>> The resulting kernel failed to boot.
>>
>> Bisecting the configurations led to CONFIG_DEBUG_VIRTUAL - if I turned it on
>> in addition to some other debug options, the machine crashed with
>>
>> kernel BUG at arch/x86/mm/physaddr.c:79!
>>
>> Screenshot at http://kodu.ut.ee/~mroos/debug_virtual-boot-hang-1.jpg
>>
>> The machine was Athlon XP with VIA KT600 chipset and 2G RAM.
>>
>> -- 
>> Meelis Roos <mroos@linux.ee>
>>
> 

You might be hitting a bug I found.
Try applying this patch:
https://marc.info/?l=linux-kernel&m=155355953012985&w=2