Subject: [PATCHv2 13/18] arm64: mm: add functions to walk tables in fixmap

From: [email-masked] (Laura Abbott)
Date: Mon, 4 Jan 2016 14:49:46 -0800

On 01/04/2016 09:56 AM, Mark Rutland wrote:
> As a prepratory step to allow us to allocate early page tables from
> unmapped memory using memblock_alloc, add new p??_fixmap* functions that
> can be used to walk page tables outside of the linear mapping by using
> fixmap slots.
>
> 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/fixmap.h  | 10 ++++++++++
>   arch/arm64/include/asm/pgtable.h | 26 ++++++++++++++++++++++++++
>   2 files changed, 36 insertions(+)
>
> diff --git a/arch/arm64/include/asm/fixmap.h b/arch/arm64/include/asm/fixmap.h
> index 3097045..1a617d4 100644
> --- a/arch/arm64/include/asm/fixmap.h
> +++ b/arch/arm64/include/asm/fixmap.h
> @@ -62,6 +62,16 @@ enum fixed_addresses {
>
>   	FIX_BTMAP_END = __end_of_permanent_fixed_addresses,
>   	FIX_BTMAP_BEGIN = FIX_BTMAP_END + TOTAL_FIX_BTMAPS - 1,
> +
> +	/*
> +	 * Used for kernel page table creation, so unmapped memory may be used
> +	 * for tables.
> +	 */
> +	FIX_PTE,
> +	FIX_PMD,
> +	FIX_PUD,
> +	FIX_PGD,
> +
>   	__end_of_fixed_addresses
>   };
>
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index f5742db..824e7f0 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -57,6 +57,7 @@
>
>   #ifndef __ASSEMBLY__
>
> +#include <asm/fixmap.h>
>   #include <linux/mmdebug.h>
>
>   extern void __pte_error(const char *file, int line, unsigned long val);
> @@ -442,6 +443,10 @@ static inline phys_addr_t pmd_page_paddr(pmd_t pmd)
>   #define pte_unmap(pte)			do { } while (0)
>   #define pte_unmap_nested(pte)		do { } while (0)
>
> +#define pte_fixmap(addr)		((pte_t *)set_fixmap_offset(FIX_PTE, addr))
> +#define pte_fixmap_offset(pmd, addr)	pte_fixmap(pte_offset_phys(pmd, addr))
> +#define pte_fixmap_unmap()		clear_fixmap(FIX_PTE)
> +
>   #define pmd_page(pmd)		pfn_to_page(__phys_to_pfn(pmd_val(pmd) & PHYS_MASK))
>
>   /*
> @@ -481,12 +486,21 @@ static inline phys_addr_t pud_page_paddr(pud_t pud)
>   #define pmd_offset_phys(dir, addr)	(pud_page_paddr(*(dir)) + pmd_index(addr) * sizeof(pmd_t))
>   #define pmd_offset(dir, addr)		((pmd_t *)__va(pmd_offset_phys((dir), (addr))))
>
> +#define pmd_fixmap(addr)		((pmd_t *)set_fixmap_offset(FIX_PMD, addr))
> +#define pmd_fixmap_offset(pud, addr)	pmd_fixmap(pmd_offset_phys(pud, addr))
> +#define pmd_fixmap_unmap()		clear_fixmap(FIX_PMD)
> +
>   #define pud_page(pud)		pfn_to_page(__phys_to_pfn(pud_val(pud) & PHYS_MASK))
>
>   #else
>
>   #define pud_page_paddr(pud)	({ BUILD_BUG(); 0; })
>
> +/* Match pmd_offset folding in <asm/generic/pgtable-nopmd.h> */
> +#define pmd_fixmap(addr)		NULL
> +#define pmd_fixmap_offset(pudp, addr)	((pmd_t *)pudp)
> +#define pmd_fixmap_unmap()
> +
>   #endif	/* CONFIG_PGTABLE_LEVELS > 2 */
>
>   #if CONFIG_PGTABLE_LEVELS > 3
> @@ -519,12 +533,21 @@ static inline phys_addr_t pgd_page_paddr(pgd_t pgd)
>   #define pud_offset_phys(dir, addr)	(pgd_page_paddr(*(dir)) + pud_index(addr) * sizeof(pud_t))
>   #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_unmap()		clear_fixmap(FIX_PUD)
> +
>   #define pgd_page(pgd)		pfn_to_page(__phys_to_pfn(pgd_val(pgd) & PHYS_MASK))
>
>   #else
>
>   #define pgd_page_paddr(pgd)	({ BUILD_BUG(); 0;})
>
> +/* Match pud_offset folding in <asm/generic/pgtable-nopud.h> */
> +#define pud_fixmap(addr)		NULL
> +#define pud_fixmap_offset(pgdp, addr)	((pud_t *)pgdp)
> +#define pud_fixmap_unmap()
> +
>   #endif  /* CONFIG_PGTABLE_LEVELS > 3 */
>
>   #define pgd_ERROR(pgd)		__pgd_error(__FILE__, __LINE__, pgd_val(pgd))
> @@ -539,6 +562,9 @@ static inline phys_addr_t pgd_page_paddr(pgd_t pgd)
>   /* to find an entry in a kernel page-table-directory */
>   #define pgd_offset_k(addr)	pgd_offset(&init_mm, addr)
>
> +#define pgd_fixmap(addr)		((pgd_t *)set_fixmap_offset(FIX_PGD, addr))
> +#define pgd_fixmap_unmap()		clear_fixmap(FIX_PGD)
> +
>   static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
>   {
>   	const pteval_t mask = PTE_USER | PTE_PXN | PTE_UXN | PTE_RDONLY |
>

Bikeshed: p??_fixmap_offset doesn't make it obvious that this is an
operation with a side effect. It seems more similar to
p??_offset_kernel which is read only. Perhaps it's the lack of set/map
in the name.

Thanks,
Laura