Subject: [PATCHv2 14/18] arm64: mm: use fixmap when creating page tables

From: [email-masked] (Laura Abbott)
Date: Mon, 4 Jan 2016 14:38:42 -0800

On 01/04/2016 09:56 AM, Mark Rutland wrote:
> As a prepratory step to allow us to allocate early page tables form
"page tables from"

> unmapped memory using memblock_alloc, modify the __create_mapping
> callees to map and unmap the tables they modify using fixmap entries.
>
> All but the top-level pgd initialisation is performed via the fixmap.
> Subsequent patches will inject the pgd physical address, and migrate to
> using the FIX_PGD slot.
>
> Signed-off-by: Mark Rutland <[email-masked]>
> Cc: Ard Biesheuvel <[email-masked]>
> Cc: Catalin Marinas <[email-masked]>
> Cc: Jeremy Linton <[email-masked]>
> Cc: Laura Abbott <[email-masked]>
> Cc: Will Deacon <[email-masked]>
> ---
>   arch/arm64/include/asm/pgtable.h |  2 +-
>   arch/arm64/mm/mmu.c              | 63 ++++++++++++++++++++++++++--------------
>   2 files changed, 42 insertions(+), 23 deletions(-)
>
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index 824e7f0..6fbf9fa 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -534,7 +534,7 @@ static inline phys_addr_t pgd_page_paddr(pgd_t pgd)
>   #define pud_offset(dir, addr)		((pud_t *)__va(pud_offset_phys((dir), (addr))))
>
>   #define pud_fixmap(addr)		((pud_t *)set_fixmap_offset(FIX_PUD, addr))
> -#define pud_fixmap_offset(pgd, addr)	pud_fixmap(pmd_offset_phys(pgd, addr))
> +#define pud_fixmap_offset(pgd, addr)	pud_fixmap(pud_offset_phys(pgd, addr))

Was this supposed to be folded into a previous patch?

>   #define pud_fixmap_unmap()		clear_fixmap(FIX_PUD)
>
>   #define pgd_page(pgd)		pfn_to_page(__phys_to_pfn(pgd_val(pgd) & PHYS_MASK))
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index 8879aed..bf09d44 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -63,19 +63,30 @@ pgprot_t phys_mem_access_prot(struct file *file, unsigned long pfn,
>   }
>   EXPORT_SYMBOL(phys_mem_access_prot);
>
> -static void __init *early_pgtable_alloc(void)
> +static phys_addr_t __init early_pgtable_alloc(void)
>   {
>   	phys_addr_t phys;
>   	void *ptr;
>
>   	phys = memblock_alloc(PAGE_SIZE, PAGE_SIZE);
>   	BUG_ON(!phys);
> -	ptr = __va(phys);
> +
> +	/*
> +	 * The FIX_{PGD,PUD,PMD} slots may be in active use, but the FIX_PTE
> +	 * slot will be free, so we can (ab)use the FIX_PTE slot to initialise
> +	 * any level of table.
> +	 */
> +	ptr = pte_fixmap(phys);
> +
>   	memset(ptr, 0, PAGE_SIZE);
>
> -	/* Ensure the zeroed page is visible to the page table walker */
> -	dsb(ishst);
> -	return ptr;
> +	/*
> +	 * Implicit barriers also ensure the zeroed page is visible to the page
> +	 * table walker
> +	 */
> +	pte_fixmap_unmap();
> +
> +	return phys;
>   }
>
>   /*
> @@ -99,24 +110,28 @@ static void split_pmd(pmd_t *pmd, pte_t *pte)
>   static void alloc_init_pte(pmd_t *pmd, unsigned long addr,
>   				  unsigned long end, unsigned long pfn,
>   				  pgprot_t prot,
> -				  void *(*pgtable_alloc)(void))
> +				  phys_addr_t (*pgtable_alloc)(void))
>   {
>   	pte_t *pte;
>
>   	if (pmd_none(*pmd) || pmd_sect(*pmd)) {
> -		pte = pgtable_alloc();
> +		phys_addr_t pte_phys = pgtable_alloc();
> +		pte = pte_fixmap(pte_phys);
>   		if (pmd_sect(*pmd))
>   			split_pmd(pmd, pte);
> -		__pmd_populate(pmd, __pa(pte), PMD_TYPE_TABLE);
> +		__pmd_populate(pmd, pte_phys, PMD_TYPE_TABLE);
>   		flush_tlb_all();
> +		pte_fixmap_unmap();
>   	}
>   	BUG_ON(pmd_bad(*pmd));
>
> -	pte = pte_offset_kernel(pmd, addr);
> +	pte = pte_fixmap_offset(pmd, addr);
>   	do {
>   		set_pte(pte, pfn_pte(pfn, prot));
>   		pfn++;
>   	} while (pte++, addr += PAGE_SIZE, addr != end);
> +
> +	pte_fixmap_unmap();
>   }
>
>   static void split_pud(pud_t *old_pud, pmd_t *pmd)
> @@ -134,7 +149,7 @@ static void split_pud(pud_t *old_pud, pmd_t *pmd)
>   static void alloc_init_pmd(struct mm_struct *mm, pud_t *pud,
>   				  unsigned long addr, unsigned long end,
>   				  phys_addr_t phys, pgprot_t prot,
> -				  void *(*pgtable_alloc)(void))
> +				  phys_addr_t (*pgtable_alloc)(void))
>   {
>   	pmd_t *pmd;
>   	unsigned long next;
> @@ -143,7 +158,8 @@ static void alloc_init_pmd(struct mm_struct *mm, pud_t *pud,
>   	 * Check for initial section mappings in the pgd/pud and remove them.
>   	 */
>   	if (pud_none(*pud) || pud_sect(*pud)) {
> -		pmd = pgtable_alloc();
> +		phys_addr_t pmd_phys = pgtable_alloc();
> +		pmd = pmd_fixmap(pmd_phys);
>   		if (pud_sect(*pud)) {
>   			/*
>   			 * need to have the 1G of mappings continue to be
> @@ -151,12 +167,13 @@ static void alloc_init_pmd(struct mm_struct *mm, pud_t *pud,
>   			 */
>   			split_pud(pud, pmd);
>   		}
> -		pud_populate(mm, pud, pmd);
> +		__pud_populate(pud, pmd_phys, PUD_TYPE_TABLE);
>   		flush_tlb_all();
> +		pmd_fixmap_unmap();
>   	}
>   	BUG_ON(pud_bad(*pud));
>
> -	pmd = pmd_offset(pud, addr);
> +	pmd = pmd_fixmap_offset(pud, addr);
>   	do {
>   		next = pmd_addr_end(addr, end);
>   		/* try section mapping first */
> @@ -182,6 +199,8 @@ static void alloc_init_pmd(struct mm_struct *mm, pud_t *pud,
>   		}
>   		phys += next - addr;
>   	} while (pmd++, addr = next, addr != end);
> +
> +	pmd_fixmap_unmap();
>   }
>
>   static inline bool use_1G_block(unsigned long addr, unsigned long next,
> @@ -199,18 +218,18 @@ static inline bool use_1G_block(unsigned long addr, unsigned long next,
>   static void alloc_init_pud(struct mm_struct *mm, pgd_t *pgd,
>   				  unsigned long addr, unsigned long end,
>   				  phys_addr_t phys, pgprot_t prot,
> -				  void *(*pgtable_alloc)(void))
> +				  phys_addr_t (*pgtable_alloc)(void))
>   {
>   	pud_t *pud;
>   	unsigned long next;
>
>   	if (pgd_none(*pgd)) {
> -		pud = pgtable_alloc();
> -		pgd_populate(mm, pgd, pud);
> +		phys_addr_t pud_phys = pgtable_alloc();
> +		__pgd_populate(pgd, pud_phys, PUD_TYPE_TABLE);
>   	}
>   	BUG_ON(pgd_bad(*pgd));
>
> -	pud = pud_offset(pgd, addr);
> +	pud = pud_fixmap_offset(pgd, addr);
>   	do {
>   		next = pud_addr_end(addr, end);
>
> @@ -243,6 +262,8 @@ static void alloc_init_pud(struct mm_struct *mm, pgd_t *pgd,
>   		}
>   		phys += next - addr;
>   	} while (pud++, addr = next, addr != end);
> +
> +	pud_fixmap_unmap();
>   }
>
>   /*
> @@ -252,7 +273,7 @@ static void alloc_init_pud(struct mm_struct *mm, pgd_t *pgd,
>   static void  __create_mapping(struct mm_struct *mm, pgd_t *pgd,
>   				    phys_addr_t phys, unsigned long virt,
>   				    phys_addr_t size, pgprot_t prot,
> -				    void *(*pgtable_alloc)(void))
> +				    phys_addr_t (*pgtable_alloc)(void))
>   {
>   	unsigned long addr, length, end, next;
>
> @@ -275,14 +296,12 @@ static void  __create_mapping(struct mm_struct *mm, pgd_t *pgd,
>   	} while (pgd++, addr = next, addr != end);
>   }
>
> -static void *late_pgtable_alloc(void)
> +static phys_addr_t late_pgtable_alloc(void)
>   {
>   	void *ptr = (void *)__get_free_page(PGALLOC_GFP);
>   	BUG_ON(!ptr);
> -
> -	/* Ensure the zeroed page is visible to the page table walker */
>   	dsb(ishst);

This dropped the comment but not the actual barrier, was that intentional?

> -	return ptr;
> +	return __pa(ptr);
>   }
>
>   static void __init create_mapping(phys_addr_t phys, unsigned long virt,
>

Thanks,
Laura