[Crash-utility] Seek help about 5-level paging

[Dou Liyang]

At 07/16/2018 06:00 PM, Kirill A. Shutemov wrote:
> On Mon, Jul 16, 2018 at 01:05:24AM +0000, Dou Liyang wrote:
>> Dear Kirill,
>>
>> Sorry to trouble you.
>>
>> I am trying to make the Crash can parse the kernel with 5-level paging.
>>
>> I met a problem, seek help.
>>
>> IMO, all user-sapce tasks must using 5-level paging if the kernel
>> has been in 5-level paging decided by '__pgtable_l5_enabled=1'. Correct?
> 
> There's no way to enable paging mode on per-task basis. It's enabled with
> flag in CR4 therefore it's global.
> 

I see,

>> And, In the Documentation/x86/x86_64/5level-paging.txt:
>>
>>    ...
>>    To mitigate this, we are not going to allocate virtual address space
>>    above 47-bit by default.
>>
>>    But userspace can ask for allocation from full address space by
>>    specifying hint address (with or without MAP_FIXED) above 47-bits.
>>    ...
>>
>> I guess it just means that some user-space tasks can't using the address
>> above 47-bits, it doesn't mean that the tasks will back to use 4-level
>> paging if the kernel has been in 5-level paging. Is it right?
> 
> Right.
> 

Thank you so much. I know what should I do in crash.

Thanks,
	dou