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SubjectRe: [PATCH] mm/memory.c: Remove pte_sw_mkyoung()
Excerpts from Andrew Morton's message of February 4, 2021 10:46 am:
> On Wed, 3 Feb 2021 10:19:44 +0000 (UTC) Christophe Leroy <christophe.leroy@csgroup.eu> wrote:
>
>> Commit 83d116c53058 ("mm: fix double page fault on arm64 if PTE_AF
>> is cleared") introduced arch_faults_on_old_pte() helper to identify
>> platforms that don't set page access bit in HW and require a page
>> fault to set it.
>>
>> Commit 44bf431b47b4 ("mm/memory.c: Add memory read privilege on page
>> fault handling") added pte_sw_mkyoung() which is yet another way to
>> manage platforms that don't set page access bit in HW and require a
>> page fault to set it.
>>
>> Remove that pte_sw_mkyoung() helper and use the already existing
>> arch_faults_on_old_pte() helper together with pte_mkyoung() instead.
>
> This conflicts with mm/memory.c changes in linux-next. In
> do_set_pte(). Please check my efforts:

I wanted to just get rid of it completely --

https://marc.info/?l=linux-mm&m=160860750115163&w=2

Waiting for MIPs to get that patch mentioned merged or nacked but
as yet seems to be no response from maintainers.

https://lore.kernel.org/linux-arch/20201019081257.32127-1-huangpei@loongson.cn/

Thanks,
Nick

>
> --- a/arch/mips/include/asm/pgtable.h~mm-memoryc-remove-pte_sw_mkyoung
> +++ a/arch/mips/include/asm/pgtable.h
> @@ -406,8 +406,6 @@ static inline pte_t pte_mkyoung(pte_t pt
> return pte;
> }
>
> -#define pte_sw_mkyoung pte_mkyoung
> -
> #ifdef CONFIG_MIPS_HUGE_TLB_SUPPORT
> static inline int pte_huge(pte_t pte) { return pte_val(pte) & _PAGE_HUGE; }
>
> --- a/include/linux/pgtable.h~mm-memoryc-remove-pte_sw_mkyoung
> +++ a/include/linux/pgtable.h
> @@ -424,22 +424,6 @@ static inline void ptep_set_wrprotect(st
> }
> #endif
>
> -/*
> - * On some architectures hardware does not set page access bit when accessing
> - * memory page, it is responsibilty of software setting this bit. It brings
> - * out extra page fault penalty to track page access bit. For optimization page
> - * access bit can be set during all page fault flow on these arches.
> - * To be differentiate with macro pte_mkyoung, this macro is used on platforms
> - * where software maintains page access bit.
> - */
> -#ifndef pte_sw_mkyoung
> -static inline pte_t pte_sw_mkyoung(pte_t pte)
> -{
> - return pte;
> -}
> -#define pte_sw_mkyoung pte_sw_mkyoung
> -#endif
> -
> #ifndef pte_savedwrite
> #define pte_savedwrite pte_write
> #endif
> --- a/mm/memory.c~mm-memoryc-remove-pte_sw_mkyoung
> +++ a/mm/memory.c
> @@ -2902,7 +2902,8 @@ static vm_fault_t wp_page_copy(struct vm
> }
> flush_cache_page(vma, vmf->address, pte_pfn(vmf->orig_pte));
> entry = mk_pte(new_page, vma->vm_page_prot);
> - entry = pte_sw_mkyoung(entry);
> + if (arch_faults_on_old_pte())
> + entry = pte_mkyoung(entry);
> entry = maybe_mkwrite(pte_mkdirty(entry), vma);
>
> /*
> @@ -3560,7 +3561,8 @@ static vm_fault_t do_anonymous_page(stru
> __SetPageUptodate(page);
>
> entry = mk_pte(page, vma->vm_page_prot);
> - entry = pte_sw_mkyoung(entry);
> + if (arch_faults_on_old_pte())
> + entry = pte_mkyoung(entry);
> if (vma->vm_flags & VM_WRITE)
> entry = pte_mkwrite(pte_mkdirty(entry));
>
> @@ -3745,8 +3747,8 @@ void do_set_pte(struct vm_fault *vmf, st
>
> if (prefault && arch_wants_old_prefaulted_pte())
> entry = pte_mkold(entry);
> - else
> - entry = pte_sw_mkyoung(entry);
> + else if (arch_faults_on_old_pte())
> + entry = pte_mkyoung(entry);
>
> if (write)
> entry = maybe_mkwrite(pte_mkdirty(entry), vma);
> _
>
>
>

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