Re: [PATCH] MIPS: make userspace mapping young by default

[Nicholas Piggin <npiggin@gmail.com>]

Excerpts from Huang Pei's message of February 4, 2021 11:39 am:
> MIPS page fault path(except huge page) takes 3 exceptions (1 TLB Miss
> + 2 TLB Invalid), butthe second TLB Invalid exception is just
> triggered by __update_tlb from do_page_fault writing tlb without
> _PAGE_VALID set. With this patch, user space mapping prot is made
> young by default (with both _PAGE_VALID and _PAGE_YOUNG set),
> and it only take 1 TLB Miss + 1 TLB Invalid exception
> 
> Remove pte_sw_mkyoung without polluting MM code and make page fault
> delay of MIPS on par with other architecture
> 
> Signed-off-by: Huang Pei <huangpei@loongson.cn>

Could we merge this? For the core code,

Reviewed-by: Nicholas Piggin <npiggin@gmail.com>

> ---
>  arch/mips/mm/cache.c    | 30 ++++++++++++++++--------------
>  include/linux/pgtable.h |  8 --------
>  mm/memory.c             |  3 ---
>  3 files changed, 16 insertions(+), 25 deletions(-)
> 
> diff --git a/arch/mips/mm/cache.c b/arch/mips/mm/cache.c
> index 23b16bfd97b2..e19cf424bb39 100644
> --- a/arch/mips/mm/cache.c
> +++ b/arch/mips/mm/cache.c
> @@ -156,29 +156,31 @@ unsigned long _page_cachable_default;
>  EXPORT_SYMBOL(_page_cachable_default);
>  
>  #define PM(p)	__pgprot(_page_cachable_default | (p))
> +#define PVA(p)	PM(_PAGE_VALID | _PAGE_ACCESSED | (p))
>  
>  static inline void setup_protection_map(void)
>  {
>  	protection_map[0]  = PM(_PAGE_PRESENT | _PAGE_NO_EXEC | _PAGE_NO_READ);
> -	protection_map[1]  = PM(_PAGE_PRESENT | _PAGE_NO_EXEC);
> -	protection_map[2]  = PM(_PAGE_PRESENT | _PAGE_NO_EXEC | _PAGE_NO_READ);
> -	protection_map[3]  = PM(_PAGE_PRESENT | _PAGE_NO_EXEC);
> -	protection_map[4]  = PM(_PAGE_PRESENT);
> -	protection_map[5]  = PM(_PAGE_PRESENT);
> -	protection_map[6]  = PM(_PAGE_PRESENT);
> -	protection_map[7]  = PM(_PAGE_PRESENT);
> +	protection_map[1]  = PVA(_PAGE_PRESENT | _PAGE_NO_EXEC);
> +	protection_map[2]  = PVA(_PAGE_PRESENT | _PAGE_NO_EXEC | _PAGE_NO_READ);
> +	protection_map[3]  = PVA(_PAGE_PRESENT | _PAGE_NO_EXEC);
> +	protection_map[4]  = PVA(_PAGE_PRESENT);
> +	protection_map[5]  = PVA(_PAGE_PRESENT);
> +	protection_map[6]  = PVA(_PAGE_PRESENT);
> +	protection_map[7]  = PVA(_PAGE_PRESENT);
>  
>  	protection_map[8]  = PM(_PAGE_PRESENT | _PAGE_NO_EXEC | _PAGE_NO_READ);
> -	protection_map[9]  = PM(_PAGE_PRESENT | _PAGE_NO_EXEC);
> -	protection_map[10] = PM(_PAGE_PRESENT | _PAGE_NO_EXEC | _PAGE_WRITE |
> +	protection_map[9]  = PVA(_PAGE_PRESENT | _PAGE_NO_EXEC);
> +	protection_map[10] = PVA(_PAGE_PRESENT | _PAGE_NO_EXEC | _PAGE_WRITE |
>  				_PAGE_NO_READ);
> -	protection_map[11] = PM(_PAGE_PRESENT | _PAGE_NO_EXEC | _PAGE_WRITE);
> -	protection_map[12] = PM(_PAGE_PRESENT);
> -	protection_map[13] = PM(_PAGE_PRESENT);
> -	protection_map[14] = PM(_PAGE_PRESENT | _PAGE_WRITE);
> -	protection_map[15] = PM(_PAGE_PRESENT | _PAGE_WRITE);
> +	protection_map[11] = PVA(_PAGE_PRESENT | _PAGE_NO_EXEC | _PAGE_WRITE);
> +	protection_map[12] = PVA(_PAGE_PRESENT);
> +	protection_map[13] = PVA(_PAGE_PRESENT);
> +	protection_map[14] = PVA(_PAGE_PRESENT);
> +	protection_map[15] = PVA(_PAGE_PRESENT);
>  }
>  
> +#undef _PVA
>  #undef PM
>  
>  void cpu_cache_init(void)
> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
> index 8fcdfa52eb4b..8c042627399a 100644
> --- a/include/linux/pgtable.h
> +++ b/include/linux/pgtable.h
> @@ -432,14 +432,6 @@ static inline void ptep_set_wrprotect(struct mm_struct *mm, unsigned long addres
>   * 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
> diff --git a/mm/memory.c b/mm/memory.c
> index feff48e1465a..95718a623884 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -2890,7 +2890,6 @@ static vm_fault_t wp_page_copy(struct vm_fault *vmf)
>  		}
>  		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);
>  		entry = maybe_mkwrite(pte_mkdirty(entry), vma);
>  
>  		/*
> @@ -3548,7 +3547,6 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf)
>  	__SetPageUptodate(page);
>  
>  	entry = mk_pte(page, vma->vm_page_prot);
> -	entry = pte_sw_mkyoung(entry);
>  	if (vma->vm_flags & VM_WRITE)
>  		entry = pte_mkwrite(pte_mkdirty(entry));
>  
> @@ -3824,7 +3822,6 @@ vm_fault_t alloc_set_pte(struct vm_fault *vmf, struct page *page)
>  
>  	flush_icache_page(vma, page);
>  	entry = mk_pte(page, vma->vm_page_prot);
> -	entry = pte_sw_mkyoung(entry);
>  	if (write)
>  		entry = maybe_mkwrite(pte_mkdirty(entry), vma);
>  	/* copy-on-write page */
> -- 
> 2.17.1
> 
> 
>