Re: vmalloc fault

[Simon Jeons <simon.jeons@gmail.com>]

Morning Rik, so early.
On 04/26/2013 06:04 PM, Rik van Riel wrote:
> On 04/26/2013 05:55 AM, Simon Jeons wrote:
>> Hi all,
>>
>> 1. Why vmalloc fault need sync user process page table with kernel page
>> table instead of using kernel page table directly?
>
> Each process has its own PGD, into which both kernel and user
> PMDs (or PUDs) are mapped. It is possible the PGD is missing
> some pointers, that need to be filled in at fault time.

It seems that you miss my question. I mean why sync page table between 
user process and init_mm.pgd, can user process use init_mm.pgd page 
table directly when access vmalloc memory? ;-)

>
>> 2. Why do_swap_page doesn't set present flag?
>
> It does.  Look at how vm_get_page_prot works.

Got it.

>
>> 3. When enable DEBUG_PAGEALLOC(catch use-after-free bug), if user
>> process alloc pages from zone_normal(which is direct mapping) when
>> fallback, this page which allocated for user process will set present
>> flag in related pte, correct? but why also set present flag for kernel
>> direct mapping? Does kernel have any requirement to access it?
>
>

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