Re: [PATCH V3 4/5] arm64: mm: introduce 52-bit userspace support

[Catalin Marinas <Catalin.Marinas@arm.com>]

On Wed, Nov 14, 2018 at 01:39:19PM +0000, Steve Capper wrote:
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index 50b1ef8584c0..19736520b724 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -616,11 +616,21 @@ static inline phys_addr_t pgd_page_paddr(pgd_t pgd)
>  #define pgd_ERROR(pgd)__pgd_error(__FILE__, __LINE__, pgd_val(pgd))
>
>  /* to find an entry in a page-table-directory */
> -#define pgd_index(addr)(((addr) >> PGDIR_SHIFT) & (PTRS_PER_PGD - 1))
> +#define pgd_index(addr, ptrs)(((addr) >> PGDIR_SHIFT) & ((ptrs) - 1))
> +#define _pgd_offset_raw(pgd, addr, ptrs) ((pgd) + pgd_index(addr, ptrs))
> +#define pgd_offset_raw(pgd, addr)(_pgd_offset_raw(pgd, addr, PTRS_PER_PGD))
>
> -#define pgd_offset_raw(pgd, addr)((pgd) + pgd_index(addr))
> +static inline pgd_t *pgd_offset(const struct mm_struct *mm, unsigned long addr)
> +{
> +pgd_t *ret;
> +
> +if (IS_ENABLED(CONFIG_ARM64_52BIT_VA) && (mm != &init_mm))
> +ret = _pgd_offset_raw(mm->pgd, addr, 1ULL << (vabits_user - PGDIR_SHIFT));

I think we can make this a constant since the additional 4 bits of the
user address should be 0 on a 48-bit VA. Once we get the 52-bit kernel
VA supported, we can probably revert back to a single macro.

Another option is to change  PTRS_PER_PGD etc. to cover the whole
52-bit, including the swapper_pg_dir, but with offsetting the TTBR1_EL1
setting to keep the 48-bit kernel VA (for the time being).

--
Catalin
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