linux-kernel - Re: [PATCH] mm: debug_vm_pgtable: Don't use _

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Date:   Fri, 24 Sep 2021 13:11:27 +0800
From:   Guo Ren <guoren@...nel.org>
To:     Anshuman Khandual <anshuman.khandual@....com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linux-MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Guo Ren <guoren@...ux.alibaba.com>
Subject: Re: [PATCH] mm: debug_vm_pgtable: Don't use __P000 directly

On Fri, Sep 24, 2021 at 11:30 AM Anshuman Khandual
<anshuman.khandual@....com> wrote:
>
> Hello Guo,
>
> On 9/22/21 1:48 AM, guoren@...nel.org wrote:
> > From: Guo Ren <guoren@...ux.alibaba.com>
> >
> > The __Pxxx/__Sxxx macros are only for init protection_map[]. All
>
> s/init protection_map[]/protection_map[] int/
                                                                   ^^^
Okay, protection_map[] init

>
> Or rephrase with something similar.
>
> > usage of them in linux should come from protection_map array.
>
> Agreed.
>
> >
> > Becasue a lot of architectures would re-initilize protection_map[]
>
> s/Becasue/Because/
>
> ./scripts/checkpatch.pl ./0001-mm-debug_vm_pgtable-Don-t-use-__P000-directly.patch
> WARNING: 'Becasue' may be misspelled - perhaps 'Because'?
> #9:
> Becasue a lot of architectures would re-initilize protection_map[]
> ^^^^^^^
>
> total: 0 errors, 1 warnings, 15 lines checked
I would use checkpatch.pl next time, thx.

>
> > array, eg: x86-mem_encrypt, m68k-motorola, mips, arm, sparc.
> >
> > Using __P000 maybe won't cause bug because hw would deny access
>
> Not very clear. Could you please rephrase.
Using __P000 directly wouldn't equal protection_map[0] in many arches,
but the reason why it didn't cause the problem is the hardware ignores
the other bits when prot-attribute is denied.

>
> > with PROT_NONE permission, but it's not rigorous.
>
> Agreed.
>
> >
> > Signed-off-by: Guo Ren <guoren@...ux.alibaba.com>
> > Cc: Andrew Morton <akpm@...ux-foundation.org>
> > ---
> >  mm/debug_vm_pgtable.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
> > index 1403639302e4..a6ebbf6e53dd 100644
> > --- a/mm/debug_vm_pgtable.c
> > +++ b/mm/debug_vm_pgtable.c
> > @@ -1104,13 +1104,13 @@ static int __init init_args(struct pgtable_debug_args *args)
> >       /*
> >        * Initialize the debugging data.
> >        *
> > -      * __P000 (or even __S000) will help create page table entries with
> > +      * __P000 (protection_map[0]) will help create page table entries with
>
> Please just replace __P000 and __S000 with protection_map[0] and
> protection_map[8] respectively. Also reformat this comment section
> if required.
>
> >        * PROT_NONE permission as required for pxx_protnone_tests().
> >        */
> >       memset(args, 0, sizeof(*args));
> >       args->vaddr              = get_random_vaddr();
> >       args->page_prot          = vm_get_page_prot(VMFLAGS);
> > -     args->page_prot_none     = __P000;
> > +     args->page_prot_none     = protection_map[0];
> >       args->is_contiguous_page = false;
> >       args->pud_pfn            = ULONG_MAX;
> >       args->pmd_pfn            = ULONG_MAX;
> >
>
> With the above changes in place.
>
> Reviewed-by: Anshuman Khandual <anshuman.khandual@....com>



-- 
Best Regards
 Guo Ren

ML: https://lore.kernel.org/linux-csky/