linux-kernel - Re: [PATCH v1] arm64: mm: Batch dsb and isb when populating pgtables

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Date: Thu, 28 Mar 2024 10:56:21 +0200
From: Ard Biesheuvel <ardb@...nel.org>
To: Ryan Roberts <ryan.roberts@....com>
Cc: Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>, 
	Mark Rutland <mark.rutland@....com>, David Hildenbrand <david@...hat.com>, 
	Donald Dutile <ddutile@...hat.com>, Eric Chanudet <echanude@...hat.com>, 
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] arm64: mm: Batch dsb and isb when populating pgtables

On Thu, 28 Mar 2024 at 10:45, Ryan Roberts <ryan.roberts@....com> wrote:
>
> On 28/03/2024 07:23, Ard Biesheuvel wrote:
> > On Wed, 27 Mar 2024 at 21:07, Ryan Roberts <ryan.roberts@....com> wrote:
> >>
> >> After removing uneccessary TLBIs, the next bottleneck when creating the
> >> page tables for the linear map is DSB and ISB, which were previously
> >> issued per-pte in __set_pte(). Since we are writing multiple ptes in a
> >> given pte table, we can elide these barriers and insert them once we
> >> have finished writing to the table.
> >>
> >
> > Nice!
> >
> >> Signed-off-by: Ryan Roberts <ryan.roberts@....com>
> >> ---
> >>  arch/arm64/include/asm/pgtable.h |  7 ++++++-
> >>  arch/arm64/mm/mmu.c              | 13 ++++++++++++-
> >>  2 files changed, 18 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> >> index bd5d02f3f0a3..81e427b23b3f 100644
> >> --- a/arch/arm64/include/asm/pgtable.h
> >> +++ b/arch/arm64/include/asm/pgtable.h
> >> @@ -271,9 +271,14 @@ static inline pte_t pte_mkdevmap(pte_t pte)
> >>         return set_pte_bit(pte, __pgprot(PTE_DEVMAP | PTE_SPECIAL));
> >>  }
> >>
> >> -static inline void __set_pte(pte_t *ptep, pte_t pte)
> >> +static inline void ___set_pte(pte_t *ptep, pte_t pte)
> >
> > IMHO, we should either use WRITE_ONCE() directly in the caller, or
> > find a better name.
>
> How about __set_pte_nosync() ?
>

Works for me.