On Wed, Jun 25, 2014 at 04:40:20PM +0100, Steve Capper wrote:
> We need a mechanism to tag ptes as being special, this indicates that
> no attempt should be made to access the underlying struct page *
> associated with the pte. This is used by the fast_gup when operating on
> ptes as it has no means to access VMAs (that also contain this
> information) locklessly.
>
> The L_PTE_SPECIAL bit is already allocated for LPAE, this patch modifies
> pte_special and pte_mkspecial to make use of it, and defines
> __HAVE_ARCH_PTE_SPECIAL.
>
> This patch also excludes special ptes from the icache/dcache sync logic.
>
> Signed-off-by: Steve Capper <steve.capper@xxxxxxxxxx>
> ---
> arch/arm/include/asm/pgtable-2level.h | 2 ++
> arch/arm/include/asm/pgtable-3level.h | 8 ++++++++
> arch/arm/include/asm/pgtable.h | 6 ++----
> 3 files changed, 12 insertions(+), 4 deletions(-)
>
> diff --git a/arch/arm/include/asm/pgtable-2level.h b/arch/arm/include/asm/pgtable-2level.h
> index 219ac88..f027941 100644
> --- a/arch/arm/include/asm/pgtable-2level.h
> +++ b/arch/arm/include/asm/pgtable-2level.h
> @@ -182,6 +182,8 @@ static inline pmd_t *pmd_offset(pud_t *pud, unsigned long addr)
> #define pmd_addr_end(addr,end) (end)
>
> #define set_pte_ext(ptep,pte,ext) cpu_set_pte_ext(ptep,pte,ext)
> +#define pte_special(pte) (0)
> +static inline pte_t pte_mkspecial(pte_t pte) { return pte; }
>
> /*
> * We don't have huge page support for short descriptors, for the moment
> diff --git a/arch/arm/include/asm/pgtable-3level.h b/arch/arm/include/asm/pgtable-3level.h
> index 85c60ad..b286ba9 100644
> --- a/arch/arm/include/asm/pgtable-3level.h
> +++ b/arch/arm/include/asm/pgtable-3level.h
> @@ -207,6 +207,14 @@ static inline pmd_t *pmd_offset(pud_t *pud, unsigned long addr)
> #define pte_huge(pte) (pte_val(pte) && !(pte_val(pte) & PTE_TABLE_BIT))
> #define pte_mkhuge(pte) (__pte(pte_val(pte) & ~PTE_TABLE_BIT))
>
> +#define pte_special(pte) (!!(pte_val(pte) & L_PTE_SPECIAL))
Why the !!? Also, shouldn't this be rebased on your series adding the
pte_isset macro to ARM?
> +static inline pte_t pte_mkspecial(pte_t pte)
> +{
> + pte_val(pte) |= L_PTE_SPECIAL;
> + return pte;
> +}
If you put this in pgtable.h based on #ifdef __HAVE_ARCH_PTE_SPECIAL, then
you can use PTE_BIT_FUNC to avoid reinventing the wheel (or define
L_PTE_SPECIAL as 0 for 2-level and have one function).
Will
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>