linux-kernel - Re: [PATCH v4 4/4] arm64: drop pfn_valid_within() and simplify pfn

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Message-ID: <CAMj1kXE=XMhr6WB+DUZYN9Fr95azn6t_B7VS3BckMPNTn_ohkg@mail.gmail.com>
Date:   Tue, 11 May 2021 12:26:10 +0200
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Mike Rapoport <rppt@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        David Hildenbrand <david@...hat.com>,
        Marc Zyngier <maz@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Will Deacon <will@...nel.org>,
        kvmarm <kvmarm@...ts.cs.columbia.edu>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Memory Management List <linux-mm@...ck.org>
Subject: Re: [PATCH v4 4/4] arm64: drop pfn_valid_within() and simplify pfn_valid()

On Tue, 11 May 2021 at 12:06, Mike Rapoport <rppt@...nel.org> wrote:
>
> From: Mike Rapoport <rppt@...ux.ibm.com>
>
> The arm64's version of pfn_valid() differs from the generic because of two
> reasons:
>
> * Parts of the memory map are freed during boot. This makes it necessary to
>   verify that there is actual physical memory that corresponds to a pfn
>   which is done by querying memblock.
>
> * There are NOMAP memory regions. These regions are not mapped in the
>   linear map and until the previous commit the struct pages representing
>   these areas had default values.
>
> As the consequence of absence of the special treatment of NOMAP regions in
> the memory map it was necessary to use memblock_is_map_memory() in
> pfn_valid() and to have pfn_valid_within() aliased to pfn_valid() so that
> generic mm functionality would not treat a NOMAP page as a normal page.
>
> Since the NOMAP regions are now marked as PageReserved(), pfn walkers and
> the rest of core mm will treat them as unusable memory and thus
> pfn_valid_within() is no longer required at all and can be disabled by
> removing CONFIG_HOLES_IN_ZONE on arm64.
>
> pfn_valid() can be slightly simplified by replacing
> memblock_is_map_memory() with memblock_is_memory().
>
> Signed-off-by: Mike Rapoport <rppt@...ux.ibm.com>
> Acked-by: David Hildenbrand <david@...hat.com>

Acked-by: Ard Biesheuvel <ardb@...nel.org>

... and many thanks for cleaning this up.


> ---
>  arch/arm64/Kconfig   | 3 ---
>  arch/arm64/mm/init.c | 2 +-
>  2 files changed, 1 insertion(+), 4 deletions(-)
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 9f1d8566bbf9..d7dc8698cf8e 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -1052,9 +1052,6 @@ config NEED_PER_CPU_EMBED_FIRST_CHUNK
>         def_bool y
>         depends on NUMA
>
> -config HOLES_IN_ZONE
> -       def_bool y
> -
>  source "kernel/Kconfig.hz"
>
>  config ARCH_SPARSEMEM_ENABLE
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index 798f74f501d5..fb07218da2c0 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -251,7 +251,7 @@ int pfn_valid(unsigned long pfn)
>         if (!early_section(ms))
>                 return pfn_section_valid(ms, pfn);
>
> -       return memblock_is_map_memory(addr);
> +       return memblock_is_memory(addr);
>  }
>  EXPORT_SYMBOL(pfn_valid);
>
> --
> 2.28.0
>