linux-kernel - Re: [PATCH] x86/mm/pti: remove dead logic during user pagetable population

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Date:   Sun, 7 Jan 2018 18:35:56 +0800
From:   Jike Song <albcamus@...il.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     luto@...nel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86/mm/pti: remove dead logic during user pagetable population

On Sun, Jan 7, 2018 at 5:48 PM, Thomas Gleixner <tglx@...utronix.de> wrote:
> On Sun, 7 Jan 2018, Jike Song wrote:
>> On Sun, Jan 7, 2018 at 3:33 AM, Thomas Gleixner <tglx@...utronix.de> wrote:
>> > On Sun, 7 Jan 2018, Jike Song wrote:
>> >
>> > Care to explain why you think this is not needed?
>> >
>>
>> Hi Thomas,
>>
>> Look at one of the original code snippets:
>>
>>     162         if (pgd_none(*pgd)) {
>>     163                 unsigned long new_p4d_page = __get_free_page(gfp);
>>     164                 if (!new_p4d_page)
>>     165                         return NULL;
>>     166
>>     167                 if (pgd_none(*pgd)) {
>>     168                         set_pgd(pgd, __pgd(_KERNPG_TABLE |
>> __pa(new_p4d_page)));
>>     169                         new_p4d_page = 0;
>>     170                 }
>>     171                 if (new_p4d_page)
>>     172                         free_page(new_p4d_page);
>>     173         }
>>
>> Correct me if I'm too dumb to see the rationale here, but to me there
>> can't be any difference between
>> two pgd_none(*pgd) of L162 and L167, so it is always false in L171.
>
> Right, but this kind of explanation wants to be in the changelog. Empty
> changelogs for this kind of change are just not acceptable.
>

Roger that, just sent v2 out :)

I'm not quite sure but I CCed stable@...nel.org anyway.


> Thanks,
>
>         tglx


-- 
Thanks,
Jike