linux-kernel - Re: [PATCH v2 3/3] LoongArch: Remove pte buddy set with set_pte and pte

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Message-ID: <CAAhV-H4-OQ4rmyztsRVsOuPra7xbzy9vcckerP8NG-7ti8jKwg@mail.gmail.com>
Date: Mon, 14 Oct 2024 14:33:24 +0800
From: Huacai Chen <chenhuacai@...nel.org>
To: Bibo Mao <maobibo@...ngson.cn>
Cc: Andrey Ryabinin <ryabinin.a.a@...il.com>, Andrew Morton <akpm@...ux-foundation.org>, 
	David Hildenbrand <david@...hat.com>, Barry Song <baohua@...nel.org>, loongarch@...ts.linux.dev, 
	linux-kernel@...r.kernel.org, kasan-dev@...glegroups.com, linux-mm@...ck.org
Subject: Re: [PATCH v2 3/3] LoongArch: Remove pte buddy set with set_pte and
 pte_clear function

Hi, Bibo,

The old code tries to fix the same problem in the first patch, so this
patch can also be squashed to the first one (and it is small enough
now).

Others look good to me.

Huacai

On Mon, Oct 14, 2024 at 11:59 AM Bibo Mao <maobibo@...ngson.cn> wrote:
>
> For kernel address space area on LoongArch system, both two consecutive
> page table entries should be enabled with PAGE_GLOBAL bit. So with
> function set_pte() and pte_clear(), pte buddy entry is checked and set
> besides its own pte entry. However it is not atomic operation to set both
> two pte entries, there is problem with test_vmalloc test case.
>
> With previous patch, all page table entries are set with PAGE_GLOBAL
> bit at beginning. Only its own pte entry need update with function
> set_pte() and pte_clear(), nothing to do with pte buddy entry.
>
> Signed-off-by: Bibo Mao <maobibo@...ngson.cn>
> ---
>  arch/loongarch/include/asm/pgtable.h | 35 ++++------------------------
>  1 file changed, 5 insertions(+), 30 deletions(-)
>
> diff --git a/arch/loongarch/include/asm/pgtable.h b/arch/loongarch/include/asm/pgtable.h
> index 22e3a8f96213..bc29c95b1710 100644
> --- a/arch/loongarch/include/asm/pgtable.h
> +++ b/arch/loongarch/include/asm/pgtable.h
> @@ -325,40 +325,15 @@ extern void paging_init(void);
>  static inline void set_pte(pte_t *ptep, pte_t pteval)
>  {
>         WRITE_ONCE(*ptep, pteval);
> -
> -       if (pte_val(pteval) & _PAGE_GLOBAL) {
> -               pte_t *buddy = ptep_buddy(ptep);
> -               /*
> -                * Make sure the buddy is global too (if it's !none,
> -                * it better already be global)
> -                */
> -               if (pte_none(ptep_get(buddy))) {
> -#ifdef CONFIG_SMP
> -                       /*
> -                        * For SMP, multiple CPUs can race, so we need
> -                        * to do this atomically.
> -                        */
> -                       __asm__ __volatile__(
> -                       __AMOR "$zero, %[global], %[buddy] \n"
> -                       : [buddy] "+ZB" (buddy->pte)
> -                       : [global] "r" (_PAGE_GLOBAL)
> -                       : "memory");
> -
> -                       DBAR(0b11000); /* o_wrw = 0b11000 */
> -#else /* !CONFIG_SMP */
> -                       WRITE_ONCE(*buddy, __pte(pte_val(ptep_get(buddy)) | _PAGE_GLOBAL));
> -#endif /* CONFIG_SMP */
> -               }
> -       }
>  }
>
>  static inline void pte_clear(struct mm_struct *mm, unsigned long addr, pte_t *ptep)
>  {
> -       /* Preserve global status for the pair */
> -       if (pte_val(ptep_get(ptep_buddy(ptep))) & _PAGE_GLOBAL)
> -               set_pte(ptep, __pte(_PAGE_GLOBAL));
> -       else
> -               set_pte(ptep, __pte(0));
> +       pte_t pte;
> +
> +       pte = ptep_get(ptep);
> +       pte_val(pte) &= _PAGE_GLOBAL;
> +       set_pte(ptep, pte);
>  }
>
>  #define PGD_T_LOG2     (__builtin_ffs(sizeof(pgd_t)) - 1)
> --
> 2.39.3
>
>