linux-kernel - Re: [PATCHv2 1/3] arm64: Drop alloc function from create

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Date:	Sat, 30 Jan 2016 11:34:50 +0100
From:	Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:	Laura Abbott <labbott@...oraproject.org>
Cc:	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Mark Rutland <mark.rutland@....com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCHv2 1/3] arm64: Drop alloc function from create_mapping

On 30 January 2016 at 00:46, Laura Abbott <labbott@...oraproject.org> wrote:
>
> create_mapping is only used in fixmap_remap_fdt. All the create_mapping
> calls need to happen on existing translation table pages without
> additional allocations. Rather than have an alloc function be called
> and fail, just set it to NULL and catch it's use. Also change

s/it's/its/

> the name to create_mapping_noalloc to better capture what exactly is
> going on.
>
> Signed-off-by: Laura Abbott <labbott@...oraproject.org>

With one nit below:
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>

> ---
>  arch/arm64/mm/mmu.c | 27 ++++++++++++++++++---------
>  1 file changed, 18 insertions(+), 9 deletions(-)
>
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index 7711554..103ebc0 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -116,7 +116,9 @@ static void alloc_init_pte(pmd_t *pmd, unsigned long addr,
>         pte_t *pte;
>
>         if (pmd_none(*pmd) || pmd_sect(*pmd)) {
> -               phys_addr_t pte_phys = pgtable_alloc();
> +               phys_addr_t pte_phys;
> +               BUG_ON(!pgtable_alloc);
> +               pte_phys = pgtable_alloc();
>                 pte = pte_set_fixmap(pte_phys);
>                 if (pmd_sect(*pmd))
>                         split_pmd(pmd, pte);
> @@ -158,7 +160,9 @@ static void alloc_init_pmd(pud_t *pud, unsigned long addr, unsigned long end,
>          * Check for initial section mappings in the pgd/pud and remove them.
>          */
>         if (pud_none(*pud) || pud_sect(*pud)) {
> -               phys_addr_t pmd_phys = pgtable_alloc();
> +               phys_addr_t pmd_phys;
> +               BUG_ON(!pgtable_alloc);
> +               pmd_phys = pgtable_alloc();
>                 pmd = pmd_set_fixmap(pmd_phys);
>                 if (pud_sect(*pud)) {
>                         /*
> @@ -223,7 +227,9 @@ static void alloc_init_pud(pgd_t *pgd, unsigned long addr, unsigned long end,
>         unsigned long next;
>
>         if (pgd_none(*pgd)) {
> -               phys_addr_t pud_phys = pgtable_alloc();
> +               phys_addr_t pud_phys;
> +               BUG_ON(!pgtable_alloc);
> +               pud_phys = pgtable_alloc();
>                 __pgd_populate(pgd, pud_phys, PUD_TYPE_TABLE);
>         }
>         BUG_ON(pgd_bad(*pgd));
> @@ -312,7 +318,10 @@ static void __create_pgd_mapping(pgd_t *pgdir, phys_addr_t phys,
>         init_pgd(pgd_offset_raw(pgdir, virt), phys, virt, size, prot, alloc);
>  }
>
> -static void __init create_mapping(phys_addr_t phys, unsigned long virt,
> +/*
> + * This function is for mapping using existing sections only.

Could you improve this comment? 'existing sections' does not quite
cover what we expect to deal with imo
> + */
> +static void __init create_mapping_noalloc(phys_addr_t phys, unsigned long virt,
>                                   phys_addr_t size, pgprot_t prot)
>  {
>         if (virt < VMALLOC_START) {
> @@ -321,7 +330,7 @@ static void __init create_mapping(phys_addr_t phys, unsigned long virt,
>                 return;
>         }
>         __create_pgd_mapping(init_mm.pgd, phys, virt, size, prot,
> -                            early_pgtable_alloc);
> +                            NULL);
>  }
>
>  void __init create_pgd_mapping(struct mm_struct *mm, phys_addr_t phys,
> @@ -680,7 +689,7 @@ void *__init fixmap_remap_fdt(phys_addr_t dt_phys)
>         /*
>          * Make sure that the FDT region can be mapped without the need to
>          * allocate additional translation table pages, so that it is safe
> -        * to call create_mapping() this early.
> +        * to call create_mapping_noalloc() this early.
>          *
>          * On 64k pages, the FDT will be mapped using PTEs, so we need to
>          * be in the same PMD as the rest of the fixmap.
> @@ -696,8 +705,8 @@ void *__init fixmap_remap_fdt(phys_addr_t dt_phys)
>         dt_virt = (void *)dt_virt_base + offset;
>
>         /* map the first chunk so we can read the size from the header */
> -       create_mapping(round_down(dt_phys, SWAPPER_BLOCK_SIZE), dt_virt_base,
> -                      SWAPPER_BLOCK_SIZE, prot);
> +       create_mapping_noalloc(round_down(dt_phys, SWAPPER_BLOCK_SIZE),
> +                       dt_virt_base, SWAPPER_BLOCK_SIZE, prot);
>
>         if (fdt_check_header(dt_virt) != 0)
>                 return NULL;
> @@ -707,7 +716,7 @@ void *__init fixmap_remap_fdt(phys_addr_t dt_phys)
>                 return NULL;
>
>         if (offset + size > SWAPPER_BLOCK_SIZE)
> -               create_mapping(round_down(dt_phys, SWAPPER_BLOCK_SIZE), dt_virt_base,
> +               create_mapping_noalloc(round_down(dt_phys, SWAPPER_BLOCK_SIZE), dt_virt_base,
>                                round_up(offset + size, SWAPPER_BLOCK_SIZE), prot);
>
>         memblock_reserve(dt_phys, size);
> --
> 2.5.0
>