linux-kernel - Re: [PATCH v4 05/36] mm: Add default definition of set

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Message-ID: <10c85f5c-3332-9130-c6f0-d36b9ea4b549@arm.com>
Date:   Thu, 25 May 2023 08:31:14 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        linux-arch@...r.kernel.org
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Mike Rapoport <rppt@...nel.org>
Subject: Re: [PATCH v4 05/36] mm: Add default definition of set_ptes()



On 3/15/23 10:44, Matthew Wilcox (Oracle) wrote:
> Most architectures can just define set_pte() and PFN_PTE_SHIFT to
> use this definition.  It's also a handy spot to document the guarantees
> provided by the MM.
> 
> Suggested-by: Mike Rapoport (IBM) <rppt@...nel.org>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> ---
>  include/linux/pgtable.h | 37 +++++++++++++++++++++++++++++++++++++
>  1 file changed, 37 insertions(+)
> 
> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
> index c5a51481bbb9..a755fe94b4b4 100644
> --- a/include/linux/pgtable.h
> +++ b/include/linux/pgtable.h
> @@ -172,6 +172,43 @@ static inline int pmd_young(pmd_t pmd)
>  }
>  #endif
>  
> +#ifndef set_ptes
> +#ifdef PFN_PTE_SHIFT
> +/**
> + * set_ptes - Map consecutive pages to a contiguous range of addresses.
> + * @mm: Address space to map the pages into.
> + * @addr: Address to map the first page at.
> + * @ptep: Page table pointer for the first entry.
> + * @pte: Page table entry for the first page.
> + * @nr: Number of pages to map.
> + *
> + * May be overridden by the architecture, or the architecture can define
> + * set_pte() and PFN_PTE_SHIFT.
> + *
> + * Context: The caller holds the page table lock.  The pages all belong
> + * to the same folio.  The PTEs are all in the same PMD.
> + */
> +static inline void set_ptes(struct mm_struct *mm, unsigned long addr,
> +		pte_t *ptep, pte_t pte, unsigned int nr)
> +{
> +	page_table_check_ptes_set(mm, addr, ptep, pte, nr);
> +
> +	for (;;) {
> +		set_pte(ptep, pte);
> +		if (--nr == 0)
> +			break;
> +		ptep++;
> +		pte = __pte(pte_val(pte) + (1UL << PFN_PTE_SHIFT));
> +	}
> +}
> +#ifndef set_pte_at
> +#define set_pte_at(mm, addr, ptep, pte) set_ptes(mm, addr, ptep, pte, 1)
> +#endif

Should not there be a build phase call out when both set_ptes() and PFN_PTE_SHIFT
are not defined on a given platform ?

--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -204,6 +204,8 @@ static inline void set_ptes(struct mm_struct *mm, unsigned long addr,
 #ifndef set_pte_at
 #define set_pte_at(mm, addr, ptep, pte) set_ptes(mm, addr, ptep, pte, 1)
 #endif
+#else
+#error "You should define PFN_PTE_SHIFT"
 #endif
 #else
 #define set_pte_at(mm, addr, ptep, pte) set_ptes(mm, addr, ptep, pte, 1)

> +#endif> +#else
> +#define set_pte_at(mm, addr, ptep, pte) set_ptes(mm, addr, ptep, pte, 1)
> +#endif
> +
>  #ifndef __HAVE_ARCH_PTEP_SET_ACCESS_FLAGS
>  extern int ptep_set_access_flags(struct vm_area_struct *vma,
>  				 unsigned long address, pte_t *ptep,