From: will.deacon@arm•com (Will Deacon)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH V4 1/2] arm: mm: Introduce {pte,pmd}_isset and {pte,pmd}_isclear
Date: Fri, 20 Jun 2014 10:12:26 +0100 [thread overview]
Message-ID: <20140620091226.GJ25104@arm.com> (raw)
In-Reply-To: <1402929159-11028-2-git-send-email-steve.capper@linaro.org>
On Mon, Jun 16, 2014 at 03:32:38PM +0100, Steve Capper wrote:
> Long descriptors on ARM are 64 bits, and some pte functions such as
> pte_dirty return a bitwise-and of a flag with the pte value. If the
> flag to be tested resides in the upper 32 bits of the pte, then we run
> into the danger of the result being dropped if downcast.
>
> For example:
> gather_stats(page, md, pte_dirty(*pte), 1);
> where pte_dirty(*pte) is downcast to an int.
>
> This patch introduces a new macro pte_isset which performs the bitwise
> and, then performs a double logical invert (where needed) to ensure
> predictable downcasting. The logical inverse pte_isclear is also
> introduced.
>
> Equivalent pmd functions for Transparent HugePages have also been
> added.
>
> Signed-off-by: Steve Capper <steve.capper@linaro•org>
> ---
> arch/arm/include/asm/pgtable-3level.h | 10 +++++++---
> arch/arm/include/asm/pgtable.h | 18 +++++++++++-------
> 2 files changed, 18 insertions(+), 10 deletions(-)
>
> diff --git a/arch/arm/include/asm/pgtable-3level.h b/arch/arm/include/asm/pgtable-3level.h
> index 85c60ad..bde49f9 100644
> --- a/arch/arm/include/asm/pgtable-3level.h
> +++ b/arch/arm/include/asm/pgtable-3level.h
> @@ -207,16 +207,20 @@ 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 pmd_young(pmd) (pmd_val(pmd) & PMD_SECT_AF)
> +#define pmd_isset(pmd, val) ((u32)(val) == (val) ? pmd_val(pmd) & (val) \
> + : !!(pmd_val(pmd) & (val)))
What does GCC generate for this as opposed to an unconditional !!?
Will
next prev parent reply other threads:[~2014-06-20 9:12 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-06-16 14:32 [PATCH V4 0/2] PTE fixes for ARM LPAE Steve Capper
2014-06-16 14:32 ` [PATCH V4 1/2] arm: mm: Introduce {pte, pmd}_isset and {pte, pmd}_isclear Steve Capper
2014-06-20 9:12 ` Will Deacon [this message]
2014-06-20 10:04 ` [PATCH V4 1/2] arm: mm: Introduce {pte,pmd}_isset and {pte,pmd}_isclear Russell King - ARM Linux
2014-06-16 14:32 ` [PATCH V4 2/2] arm: mm: Switch back to L_PTE_WRITE Steve Capper
2014-06-20 9:21 ` Will Deacon
2014-06-20 13:23 ` Steve Capper
2014-06-20 18:17 ` Russell King - ARM Linux
2014-06-23 11:17 ` Catalin Marinas
2014-06-23 15:07 ` Steve Capper
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