linux-kernel - Re: [PATCH v4] riscv: mm: Remove the copy operation of pmd

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Message-ID: <mhng-2e84f176-f077-4a7a-b1e0-66813b2c0e7d@palmer-ri-x1c9>
Date:   Thu, 21 Apr 2022 10:05:36 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...belt.com>
To:     hanchuanhua@...o.com
CC:     Paul Walmsley <paul.walmsley@...ive.com>, aou@...s.berkeley.edu,
        alexandre.ghiti@...onical.com, jszhang@...nel.org,
        mhiramat@...nel.org, akpm@...ux-foundation.org,
        zhengqi.arch@...edance.com, ebiederm@...ssion.com,
        liushixin2@...wei.com, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org, hanchuanhua@...o.com
Subject:     Re: [PATCH v4] riscv: mm: Remove the copy operation of pmd

On Thu, 31 Mar 2022 19:43:20 PDT (-0700), hanchuanhua@...o.com wrote:
> Since all processes share the kernel address space,
> we only need to copy pgd in case of a vmalloc page
> fault exception, the other levels of page tables are
> shared, so the operation of copying pmd is unnecessary.
>
> Signed-off-by: Chuanhua Han <hanchuanhua@...o.com>
> ---
> Changes in v4:
>   -Modify incorrect author name.
>
> Changes in v3:
>   -Change the real name of signed-off-by.
>
> Changes in v2:
>   -Delete incorrect default signatures.
>
>
>  arch/riscv/mm/fault.c | 10 +++-------
>  1 file changed, 3 insertions(+), 7 deletions(-)
>
> diff --git a/arch/riscv/mm/fault.c b/arch/riscv/mm/fault.c
> index 4e9efbe46d5f..40694f0cab9e 100644
> --- a/arch/riscv/mm/fault.c
> +++ b/arch/riscv/mm/fault.c
> @@ -102,9 +102,9 @@ static inline void bad_area(struct pt_regs *regs, struct mm_struct *mm, int code
>  static inline void vmalloc_fault(struct pt_regs *regs, int code, unsigned long addr)
>  {
>  	pgd_t *pgd, *pgd_k;
> -	pud_t *pud, *pud_k;
> -	p4d_t *p4d, *p4d_k;
> -	pmd_t *pmd, *pmd_k;
> +	pud_t *pud_k;
> +	p4d_t *p4d_k;
> +	pmd_t *pmd_k;
>  	pte_t *pte_k;
>  	int index;
>  	unsigned long pfn;
> @@ -132,14 +132,12 @@ static inline void vmalloc_fault(struct pt_regs *regs, int code, unsigned long a
>  	}
>  	set_pgd(pgd, *pgd_k);
>
> -	p4d = p4d_offset(pgd, addr);
>  	p4d_k = p4d_offset(pgd_k, addr);
>  	if (!p4d_present(*p4d_k)) {
>  		no_context(regs, addr);
>  		return;
>  	}
>
> -	pud = pud_offset(p4d, addr);
>  	pud_k = pud_offset(p4d_k, addr);
>  	if (!pud_present(*pud_k)) {
>  		no_context(regs, addr);
> @@ -150,13 +148,11 @@ static inline void vmalloc_fault(struct pt_regs *regs, int code, unsigned long a
>  	 * Since the vmalloc area is global, it is unnecessary
>  	 * to copy individual PTEs
>  	 */
> -	pmd = pmd_offset(pud, addr);
>  	pmd_k = pmd_offset(pud_k, addr);
>  	if (!pmd_present(*pmd_k)) {
>  		no_context(regs, addr);
>  		return;
>  	}
> -	set_pmd(pmd, *pmd_k);
>
>  	/*
>  	 * Make sure the actual PTE exists as well to

Thanks, this is on for-next (it was last night, but looks like I forgot 
to send the email).