linux-kernel - Re: [PATCH 01/30] x86, mm: do not set _PAGE_USER for init

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Date:   Wed, 8 Nov 2017 12:11:01 -0800
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        moritz.lipp@...k.tugraz.at,
        Daniel Gruss <daniel.gruss@...k.tugraz.at>,
        michael.schwarz@...k.tugraz.at, richard.fellner@...dent.tugraz.at,
        Andrew Lutomirski <luto@...nel.org>,
        Kees Cook <keescook@...gle.com>,
        Hugh Dickins <hughd@...gle.com>,
        the arch/x86 maintainers <x86@...nel.org>
Subject: Re: [PATCH 01/30] x86, mm: do not set _PAGE_USER for init_mm page
 tables

On 11/08/2017 11:52 AM, Linus Torvalds wrote:
> On Wed, Nov 8, 2017 at 11:46 AM, Dave Hansen
> <dave.hansen@...ux.intel.com> wrote:
>>
>> +
>>  static inline void pmd_populate_kernel(struct mm_struct *mm,
>>                                        pmd_t *pmd, pte_t *pte)
>>  {
>> +       pteval_t pgtable_flags = mm_pgtable_flags(mm);
> 
> Why is "pmd_populate_kernel()" using mm_pgtable_flags(mm)?
> 
> It should just use _KERNPG_TABLE unconditionally, shouldn't it?
> Nothing to do with init_mm, it's populating a _kernel_ page table
> regardless, no?

The end result is probably the same since a quick grep shows it only
ever getting called with init_mm or NULL.  But, yeah, it should probably
just be _PAGE_KERNEL directly.

I'll update it.