Date: Tue, 16 Dec 2014 06:29:38 +0000 (GMT)
From: Jongman Heo <jongman.heo@samsung.com>
Subject: Re: Re: [3.18+] Can't boot with commit bd809af1
 ("x86: Enable PAT to use cache mode translation tables")
To: Juergen Gross <jgross@suse.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Reply-to: jongman.heo@samsung.com
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>
>------- Original Message -------
>Sender : Juergen Gross<jgross@suse.com>
>Date : 2014-12-16 14:14 (GMT+09:00)
>Title : Re: [3.18+] Can't boot with commit bd809af1 ("x86: Enable PAT to use cache mode translation tables")
>
>On 12/16/2014 05:40 AM, Jongman Heo wrote:
>>> ------- Original Message -------
>>> Sender : Juergen Gross
>>> Date : 2014-12-15 20:52 (GMT+09:00)
>>> Title : Re: [3.18+] Can't boot with commit bd809af1 ("x86: Enable PAT to use cache mode translation tables")
>>>
>>> On 12/15/2014 08:52 AM, Jongman Heo wrote:
>>>>> ------- Original Message -------
>>>>> Sender : Juergen Gross
>>>>> Date : 2014-12-15 14:04 (GMT+09:00)
>>>>> Title : Re: [3.18+] Can't boot with commit bd809af1 ("x86: Enable PAT to use cache mode translation tables")
>>>>>
>>>>> On 12/14/2014 06:07 AM, ?????? wrote:
>>>>>>
>>>>>> Hi,
>>>>>>
>>>>>> My Linux virtual machine on (Windows) VMWare workstation 10 can't boot with following commit.
>>>>>>
>>>>>> commit bd809af16e3ab1f8d55b3e2928c47c67e2a865d2
>>>>>> Author: Juergen Gross
>>>>>> Date:   Mon Nov 3 14:02:03 2014 +0100
>>>>>>
>>>>>>        x86: Enable PAT to use cache mode translation tables
>>>>>>
>>>>>> Unfortunately I can't see any console log.
>>>>>
>>>>> Hmm, weird. Could you provide some more information?
>>>>>
>>>>> Kernel config, hardware used, /proc/cpuinfo of working kernel?
>>>>> Anything you see with earlyprintk enabled?
>>>>>
>>>>>
>>>>> Juergen
>>>>
>>>> (Sorry for resending this email, previous one bounced from mailing list due to HTML format)
>>>>
>>>> Hi,
>>>>
>>>> I'm using Fedora 21, with custom built kernel.
>>>> Host PC is windows 7 64-bit, and running VMWare workstation 10 for guest Fedora Linux.
>>>>
>>>> With earlyprintk, just following message is printed.
>>>>
>>>>     early console in setup code
>>>>
>>>> and nothing more...
>>>
>>> Can you try attached diagnostic patch, please? I suspect a problem
>>> regarding VMWares PAT emulation...
>>>
>>>
>>> Juergen
>> 
>> Hi,
>> 
>> With the commit reverted, the patch doesn't apply.
>
>Sure.
>
>> Without revert, kernel (patch applied) doesn't boot and I can't see any message.
>
>What are your kernel parameters? There must be some message with the
>diagnostic patch, as the first pr_info() is called before any other
>part of the critical patch is becoming active. Could it be you have
>instructed the kernel to be "quiet"? I'd recommend:
>
>earlyprintk=vga ignore_loglevel
>
>and no quiet. I don't know VMWare settings, so may be you can use
>earlyprintk=ttyS0 instead of vga.
>
>> 
>> Let me show you my PAT values (the commit reverted)
>> 
>> # dmesg | grep PAT
>> [    0.000000] x86 PAT enabled: cpu 0, old 0x0, new 0x7010600070106
>> [    0.314631] x86 PAT enabled: cpu 3, old 0x0, new 0x7010600070106
>> [    0.314703] x86 PAT enabled: cpu 1, old 0x0, new 0x7010600070106
>> [    0.314780] x86 PAT enabled: cpu 2, old 0x0, new 0x7010600070106
>> [    0.314852] x86 PAT enabled: cpu 4, old 0x0, new 0x7010600070106
>> [    0.314923] x86 PAT enabled: cpu 0, old 0x0, new 0x7010600070106
>> [    0.314997] x86 PAT enabled: cpu 6, old 0x0, new 0x7010600070106
>> [    0.315069] x86 PAT enabled: cpu 7, old 0x0, new 0x7010600070106
>> [    0.315142] x86 PAT enabled: cpu 5, old 0x0, new 0x7010600070106
>
>These are the expected values. But these values are the ones which are
>written, not the ones which have been read from the PAT MSR again.
>
>Without applying the critical patch you could add:
>
>rdmsrl(MSR_IA32_CR_PAT, pat);
>printk(KERN_INFO "PAT read: cpu %d, 0x%Lx\n", smp_processor_id(), pat);
>
>at the end of pat_init() to verify VMWare is handling reads of the PAT
>MSR properly.
>
>Juergen
>

Hi,

With earlyprintk=vga, I can see the log.
But due to call trace, I can't see what the pat value is.

Call chain is as follows.

  i386_start_kernel -> start_kernel -> setup_arch -> 
  mtrr_bp_init -> get_mtrr_state -> pat_init ->
  pat_init_cache_mode_entry -> update_cache_mode_entry -> 
  early_idt_handler -> dump_stack

So, I blocked update_cache_mode_entry() call like below...

--- a/arch/x86/mm/pat.c
+++ b/arch/x86/mm/pat.c
@@ -182,11 +182,12 @@ void pat_init_cache_modes(void)
        u64 pat;
 
        rdmsrl(MSR_IA32_CR_PAT, pat);
+       pr_info("read pat %0llx\n", pat);
        pat_msg[32] = 0;
        for (i = 7; i >= 0; i--) {
                cache = pat_get_cache_mode((pat >> (i * 8)) & 7,
                                           pat_msg + 4 * i);
-               update_cache_mode_entry(i, cache);
+               //update_cache_mode_entry(i, cache);
        }
        pr_info("PAT configuration [0-7]: %s\n", pat_msg);
 }
@@ -238,9 +239,13 @@ void pat_init(void)
                rdmsrl(MSR_IA32_CR_PAT, boot_pat_state);
 
        wrmsrl(MSR_IA32_CR_PAT, pat);
+       pr_info("about to write pat %0llx\n", pat);
 
        if (boot_cpu)
                pat_init_cache_modes();
+
+       rdmsrl(MSR_IA32_CR_PAT, pat);
+       printk(KERN_INFO "PAT read: cpu %d, 0x%Lx\n", smp_processor_id(), pat);
 }
 

Then boot is fine, and PAT values are as follows. 


# dmesg|grep -i "pat "
[    0.000000] about to write pat 7010600070106
[    0.000000] read pat 0
[    0.000000] PAT configuration [0-7]: UC  UC  UC  UC  UC  UC  UC  UC  
[    0.000000] PAT read: cpu 0, 0x0
[    0.320559] about to write pat 7010600070106
[    0.320876] read pat 0
[    0.321090] PAT configuration [0-7]: UC  UC  UC  UC  UC  UC  UC  UC  
[    0.321260] PAT read: cpu 5, 0x0
[    0.321403] about to write pat 7010600070106
[    0.321818] read pat 0
[    0.322033] PAT configuration [0-7]: UC  UC  UC  UC  UC  UC  UC  UC  
[    0.322205] PAT read: cpu 6, 0x0
[    0.322334] about to write pat 7010600070106
[    0.322417] read pat 0
[    0.322479] PAT configuration [0-7]: UC  UC  UC  UC  UC  UC  UC  UC  
[    0.322573] PAT read: cpu 0, 0x0
[    0.322703] about to write pat 7010600070106
[    0.323012] read pat 0
[    0.323228] PAT configuration [0-7]: UC  UC  UC  UC  UC  UC  UC  UC  
[    0.323400] PAT read: cpu 1, 0x0
[    0.323537] about to write pat 7010600070106
[    0.323833] read pat 0
[    0.324055] PAT configuration [0-7]: UC  UC  UC  UC  UC  UC  UC  UC  
[    0.324224] PAT read: cpu 7, 0x0
[    0.324362] about to write pat 7010600070106
[    0.324662] read pat 0
[    0.324877] PAT configuration [0-7]: UC  UC  UC  UC  UC  UC  UC  UC  
[    0.325048] PAT read: cpu 2, 0x0
[    0.325185] about to write pat 7010600070106
[    0.325483] read pat 0
[    0.325695] PAT configuration [0-7]: UC  UC  UC  UC  UC  UC  UC  UC  
[    0.325863] PAT read: cpu 4, 0x0
[    0.325997] about to write pat 7010600070106
[    0.326288] read pat 0
[    0.326507] PAT configuration [0-7]: UC  UC  UC  UC  UC  UC  UC  UC  
[    0.326677] PAT read: cpu 3, 0x0
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