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

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Message-ID: <e5c0cfdf-315c-836c-8be7-9f952ac0cd9e@oppo.com>
Date:   Wed, 23 Feb 2022 10:58:12 +0800
From:   hanchuanhua <hanchuanhua@...o.com>
To:     Palmer Dabbelt <palmer@...belt.com>
Cc:     Paul Walmsley <paul.walmsley@...ive.com>,
        "aou@...s.berkeley.edu" <aou@...s.berkeley.edu>,
        "jszhang@...nel.org" <jszhang@...nel.org>,
        "alexandre.ghiti@...onical.com" <alexandre.ghiti@...onical.com>,
        "wangkefeng.wang@...wei.com" <wangkefeng.wang@...wei.com>,
        "zhengqi.arch@...edance.com" <zhengqi.arch@...edance.com>,
        "ebiederm@...ssion.com" <ebiederm@...ssion.com>,
        "liushixin2@...wei.com" <liushixin2@...wei.com>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] riscv: mm: Remove the copy operation of pmd


On 2022/2/23 5:25, Palmer Dabbelt wrote:
> On Thu, 27 Jan 2022 02:06:22 PST (-0800), 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: hanchuanhua <hanchuanhua@...o.com>
>> ---
>>   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 4e9efbe..40694f0 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
> This looks good, but "Signed off by" lines are supposed to have real
> names associated with them and this looks like a handle to me.  There
> also seems to be something broken with the email, as this is causing git
> to blow up, but for a small patch like this that's OK as I can resurrect
> it by hand.
>
> Reviewed-by: Palmer Dabbelt <palmer@...osinc.com> # aside from the name
>
> Please send a v2 with the proper Signed off by line, as that's not
> something I'm supposed to just fix up myself.
>
> Thanks!

First of all, thank you for your review and reply. I don't quite
understand what's wrong with the line "Signed off by"?

Thanks!

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