Re: Re: [3.18+] Can't boot with commit bd809af1 ("x86: Enable PAT to use cache mode translation tables")

From: Jongman Heo
Date: Tue Dec 16 2014 - 01:29:45 EST

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In reply to: Juergen Gross: "Re: [3.18+] Can't boot with commit bd809af1 ("x86: Enable PAT to use cache mode translation tables")"
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>
>------- Original Message -------
>Sender : Juergen Gross<jgross@xxxxxxxx>
>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, 허종만 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

Next message: Fengguang Wu: "Re: [LKP] [userns] BUG: unable to handle kernel NULL pointer dereference at (null)"
Previous message: Arun KS: "Re: [RCU] kernel hangs in wait_rcu_gp during suspend path"
In reply to: Juergen Gross: "Re: [3.18+] Can't boot with commit bd809af1 ("x86: Enable PAT to use cache mode translation tables")"
Next in thread: Juergen Gross: "Re: [3.18+] Can't boot with commit bd809af1 ("x86: Enable PAT to use cache mode translation tables")"
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