Re: [PATCH v3 06/21] arm64: pgtable: implement static [pte|pmd|pud]_offset variants

Mark Rutland
2016-01-11T16:25:16Z

On Mon, Jan 11, 2016 at 02:18:59PM +0100, Ard Biesheuvel wrote:
> The page table accessors pte_offset(), pud_offset() and pmd_offset()
> rely on __va translations, so they can only be used after the linear
> mapping has been installed. For the early fixmap and kasan init routines,
> whose page tables are allocated statically in the kernel image, these
> functions will return bogus values. So implement pmd_offset_kimg() and
> pud_offset_kimg(), which can be used instead before any page tables have
> been allocated dynamically.
>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>

This looks good to me. One possible suggsetion below, but either way:

Reviewed-by: Mark Rutland <mark.rutland@arm.com>

> ---
> arch/arm64/include/asm/pgtable.h | 13 +++++++++++++
> 1 file changed, 13 insertions(+)
>
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index 6129f6755081..7b4e16068c9f 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -449,6 +449,9 @@ static inline phys_addr_t pmd_page_paddr(pmd_t pmd)
>
> #define pmd_page(pmd) pfn_to_page(__phys_to_pfn(pmd_val(pmd) & PHYS_MASK))
>
> +/* use ONLY for statically allocated translation tables */
> +#define pte_offset_kimg(dir,addr) ((pte_t *)__phys_to_kimg(pte_offset_phys((dir), (addr))))
> +

Given that we're probably only going to use this during one-off setup,
maybe it's worth something like:

#define IN_KERNEL_IMAGE(p) ({ \
unsigned long __p = (unsigned long)p; \
KIMAGE_VADDR <= __p && __p < _end; \
})

#define pte_offset_kimg(dir,addr) ({ \
BUG_ON(!IN_KERNEL_IMAGE(dir)); \
((pte_t *)__phys_to_kimg(pte_offset_phys((dir), (addr)))); \
})

That might be overkill, though, given all it does is turn one runtime
failure into another runtime failure.

Mark.

> /*
> * Conversion functions: convert a page and protection to a page entry,
> * and a page entry and page directory to the page they refer to.
> @@ -492,6 +495,9 @@ static inline phys_addr_t pud_page_paddr(pud_t pud)
>
> #define pud_page(pud) pfn_to_page(__phys_to_pfn(pud_val(pud) & PHYS_MASK))
>
> +/* use ONLY for statically allocated translation tables */
> +#define pmd_offset_kimg(dir,addr) ((pmd_t *)__phys_to_kimg(pmd_offset_phys((dir), (addr))))
> +
> #else
>
> #define pud_page_paddr(pud) ({ BUILD_BUG(); 0; })
> @@ -502,6 +508,8 @@ static inline phys_addr_t pud_page_paddr(pud_t pud)
> #define pmd_set_fixmap_offset(pudp, addr) ((pmd_t *)pudp)
> #define pmd_clear_fixmap()
>
> +#define pmd_offset_kimg(dir,addr) ((pmd_t *)dir)
> +
> #endif /* CONFIG_PGTABLE_LEVELS > 2 */
>
> #if CONFIG_PGTABLE_LEVELS > 3
> @@ -540,6 +548,9 @@ static inline phys_addr_t pgd_page_paddr(pgd_t pgd)
>
> #define pgd_page(pgd) pfn_to_page(__phys_to_pfn(pgd_val(pgd) & PHYS_MASK))
>
> +/* use ONLY for statically allocated translation tables */
> +#define pud_offset_kimg(dir,addr) ((pud_t *)__phys_to_kimg(pud_offset_phys((dir), (addr))))
> +
> #else
>
> #define pgd_page_paddr(pgd) ({ BUILD_BUG(); 0;})
> @@ -550,6 +561,8 @@ static inline phys_addr_t pgd_page_paddr(pgd_t pgd)
> #define pud_set_fixmap_offset(pgdp, addr) ((pud_t *)pgdp)
> #define pud_clear_fixmap()
>
> +#define pud_offset_kimg(dir,addr) ((pud_t *)dir)
> +
> #endif /* CONFIG_PGTABLE_LEVELS > 3 */
>
> #define pgd_ERROR(pgd) __pgd_error(__FILE__, __LINE__, pgd_val(pgd))
> --
> 2.5.0
>