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Date: Tue, 16 Dec 2014 07:36:24 +0100
From: Juergen Gross <jgross@...e.com>
To: jongman.heo@...sung.com,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [3.18+] Can't boot with commit bd809af1 ("x86: Enable PAT to
use cache mode translation tables")
On 12/16/2014 07:29 AM, Jongman Heo wrote:
>>
>> ------- Original Message -------
>> Sender : Juergen Gross<jgross@...e.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, ÇãÁ¾¸¸ 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
Okay, so VMWare doesn't seem to return the correct PAT MSR value.
I suggest you try "nopat" as kernel option. This should disable all the
PAT handling and VMWare can't wreck the kernel this way.
I'll write a patch which detects this VMWare bug by checking the PAT
value after writing it.
Thanks for reporting that case,
Juergen
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