Re: -tip tree resume fail, bisect to 5bd5a45(x86: Add NX protection for kernel data)

On Tue, Jan 25, 2011 at 6:22 AM, matthieu castet
<castet.matthieu <at> free.fr> wrote:
> matthieu castet a écrit :
>>
>> Lin Ming a écrit :
>>>
>>> On Tue, 2010-11-30 at 19:27 +0800, Peter Zijlstra wrote:
>>>>
>>>> On Tue, 2010-11-30 at 13:00 +0800, Lin Ming wrote:
>>>>>
>>>>> echo 0 > /sys/devices/system/cpu/cpu1/online;
>>>>> echo 1 > /sys/devices/system/cpu/cpu1/online;
>>>>>
>>>>> then machine just reboots...
>>>>>
>> I tried to do the same thing on qemu, and the same behavior happened (ie
>> reboot when resuming cpu1).
>>
>> After enabling qemu log, I found that a triple fault was happening at the
>> beginning of secondary_startup_64
>> when doing "addq phys_base(%rip), %rax".
>>
>> Why ?
>> I suppose because we access data set to NX, but we don't have enabled yet
>> NX in the msr. So the cpu crash due to "reserved bit check".
>>
>> If we enable NX before reading data, there is no more crash (patch
>> attached).
>>
>> Now I am not sure this is the correct fix. I think the problem is that
>> trampoline using kernel page table
>> is very dangerous. The kernel can have modified them atfer booting !
>> May be all the paging stuff should have been done in head_64.S. A first
>> one with identity mapping, and the second one for
>> the real kernel stuff.
>>
> Lin, could you try this patch on your x64 machine.

Hi,

I'm on holiday now.
I'll test it when I'm back on Feb 9.

Thanks,
Lin Ming

>
>
> Thanks
>
> Matthieu
>
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