From: Will Deacon <will.deacon@arm.com>
To: Steve Capper <steve.capper@linaro.org>
Cc: "linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
Catalin Marinas <Catalin.Marinas@arm.com>,
"linux@arm.linux.org.uk" <linux@arm.linux.org.uk>,
"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"gary.robertson@linaro.org" <gary.robertson@linaro.org>,
"christoffer.dall@linaro.org" <christoffer.dall@linaro.org>,
"peterz@infradead.org" <peterz@infradead.org>,
"anders.roxell@linaro.org" <anders.roxell@linaro.org>,
"akpm@linux-foundation.org" <akpm@linux-foundation.org>
Subject: Re: [PATCH 2/6] arm: mm: Introduce special ptes for LPAE
Date: Fri, 27 Jun 2014 13:17:21 +0100 [thread overview]
Message-ID: <20140627121721.GM26276@arm.com> (raw)
In-Reply-To: <1403710824-24340-3-git-send-email-steve.capper@linaro.org>
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@linaro.org>
> ---
> 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
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next prev parent reply other threads:[~2014-06-27 12:17 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-06-25 15:40 [PATCH 0/6] RCU get_user_pages_fast and __get_user_pages_fast Steve Capper
2014-06-25 15:40 ` [PATCH 1/6] mm: Introduce a general RCU get_user_pages_fast Steve Capper
2014-06-25 15:40 ` [PATCH 2/6] arm: mm: Introduce special ptes for LPAE Steve Capper
2014-06-27 12:17 ` Will Deacon [this message]
2014-06-27 12:44 ` Steve Capper
2014-06-25 15:40 ` [PATCH 3/6] arm: mm: Enable HAVE_RCU_TABLE_FREE logic Steve Capper
2014-06-25 15:40 ` [PATCH 4/6] arm: mm: Enable RCU fast_gup Steve Capper
2014-06-25 15:40 ` [PATCH 5/6] arm64: mm: Enable HAVE_RCU_TABLE_FREE logic Steve Capper
2014-06-25 15:40 ` [PATCH 6/6] arm64: mm: Enable RCU fast_gup Steve Capper
2014-06-25 16:50 ` Mark Rutland
2014-06-26 7:56 ` Peter Zijlstra
2014-06-27 12:20 ` Will Deacon
2014-06-25 20:42 ` [PATCH 0/6] RCU get_user_pages_fast and __get_user_pages_fast Andrew Morton
2014-06-26 7:53 ` Peter Zijlstra
2014-08-20 14:56 ` Dann Frazier
2014-08-20 15:11 ` Steve Capper
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