Re: [Help Test] kdump, x86, acpi: Reproduce CPU0 SMI corruption issue after unsetting BSP flag

Jingbai Ma
2013-08-14T09:13:37Z

On 08/13/2013 06:55 PM, Jingbai Ma wrote:
> On 08/06/2013 05:19 PM, HATAYAMA Daisuke wrote:
>> Hello,
>>
>> I've addressing kdump restriction that there's only one cpu available
>> on the kdump 2nd kernel. Now I need to check if the following CPU0 SMI
>> corruption issue fixed in the following commit can again be reproduced
>> by unsetting BSP flag of the boot cpu:
>>
>> commit 74b5820808215f65b70b05a099d6d3c969b82689
>> Author: Bjorn Helgaas<bjorn.helgaas@hp.com>
>> Date: Wed Jul 29 15:54:25 2009 -0600
>>
>> ACPI: bind workqueues to CPU 0 to avoid SMI corruption
>>
>> On some machines, a software-initiated SMI causes corruption unless the
>> SMI runs on CPU 0. An SMI can be initiated by any AML, but typically it's
>> done in GPE-related methods that are run via workqueues, so we can avoid
>> the known corruption cases by binding the workqueues to CPU 0.
>>
>> References:
>> http://bugzilla.kernel.org/show_bug.cgi?id=13751
>> https://bugs.launchpad.net/bugs/157171
>> https://bugs.launchpad.net/bugs/157691
>>
>> Signed-off-by: Bjorn Helgaas<bjorn.helgaas@hp.com>
>> Signed-off-by: Len Brown<len.brown@intel.com>
>>
>> The reason is that in the current situation, I have two ideas to deal
>> with the avove kdump restriction:
>>
>> 1) Disable BSP at the 2nd kernel, posted at:
>> [PATCH v1 0/2] x86, apic: Disable BSP if boot cpu is AP
>> https://lkml.org/lkml/2012/10/16/15
>>
>> 2) Unset BSP flag at the 1st kernel, suggested by Eric Biederman
>> during the discussion of the idea 1).
>>
>> On the idea 1), BSP is disabled on the kdump 2nd kernel. My conclusion
>> is that we have no method to reset BSP, i.e. recover BPS's healthy
>> state, while we can recover AP by means of INIT as described in MP
>> specification.
>>
>> The idea 2) is simpler. We unset BSP flag of the boot cpu at 1st
>> kernel. The behaviour when receiving INIT depends on whether or not
>> BSP flag is set or not on its MSR; we can set and unset BSP flag of
>> MSR freely at runtime. (I don't mean we should).
>>
>> So, next thing I should do is to evalute risk of the idea 2). In fact,
>> during the discussion of the idea 1), HPA pointed out that some kind
>> of firmware affects if BSP flag is unset. Also, maybe from the same
>> reason, recently introduced cpu0 hot-plugging feature by Fenghua Yu
>> doesn't appear to unset BSP flag.
>>
>> The biggest problem next is that I don't have any machines reported in
>> the bugzilla articles; this issue inherently depends on firmware.
>>
>> So, could anyone help testing the idea 2) above if you have which of
>> the following machines? (or other ones that can lead to the same bug)
>>
>> - HP Compaq 6910p
>> - HP Compaq 6710b
>> - HP Compaq 6710s
>> - HP Compaq 6510b
>> - HP Compaq 2510p
>>
>> I prepared a small programs for this test. See the attached file.
>> The steps to try to reproduce the bug is as follows:
>>
>> 1. $ tar xf bsp_flag_modules.tar.gz; cd bsp_flag_modules
>> 2. $ make # to build these programs
>> 3. $ insmod unsetbspflag.ko # to unset BSP flag of the boot cpu
>> 4. $ insmod getcpuinfo.ko # to confirm if BSP flag of the boot cpu has
>> # been unset.
>> $ dmesg | tail
>> 5. Close the lid of the machine.
>> 6. Wait some minutes if necessary.
>> 7. Open the lid and you can see oops on the screen if bug has
>> successfully been reproduced.
>>
>
> I couldn't find any model list above, but found one HP EliteBook 6930p.
> I tested this machine with kernel 2.6.30 first. After resuming from
> suspend, system hang.
>
> Then, I tested with kernel 3.11.0-rc5, it worked well, could resume from
> suspend without any problem.
>
> Next, I tested your program to clear BSP flag, I found the
> unsetbspflag.ko didn't work everytime, sometimes I have to execute
> insmod/rmmod several times to clear the BSP flag. (I used your
> getcpuinfo.ko to check the BSP flag)
>
> cpu: 0 bios_apic: 0 apic: 0 AP
> cpu: 1 bios_apic: 1 apic: 1 AP
>
> I suspended it, and them resumed it. This machine resumed from suspend
> successfully, but the BSP flag has been set back:
>
> cpu: 0 bios_apic: 0 apic: 0 BSP
> cpu: 1 bios_apic: 1 apic: 1 AP
>
> That's all my observation. Hope it's helpful.
>

I found a side effect of unsetting BSP flag.
It affected system rebooting, once the BSP flags been removed, and issue
reboot command, system will hang after message:
Restarting system.
And have to do a hardware reset to recover it.

I have reproduced this problem on the following systems:
HP EliteBook 6930p
HP Compaq DC7700
HP ProLiant DL980 (4 sockets, 40 cores)

I have an idea: To avoid such kind of issue, we can unset BSP flag in
the first kernel during crash processing, and restore it in the second
kernel in the APs initializing.

--
Thanks,
Jingbai Ma