[RFC PATCH 00/10] arm64: restrict __pa translation to linear virtual addresses

[Ard Biesheuvel]

On 22 February 2016 at 21:54, Ard Biesheuvel <ard.biesheuvel at linaro.org> wrote:
> As pointed out by Will, performing non-trivial arithmetic in the implementation
> of __pa() may affect performance. So instead of allowing __pa() to deal with
> addresses that are either covered by the kernel mappin in the vmalloc area, or
> by the linear region, let's restrict ourselves to the latter.
>
> This involves replacing some __pa() translations with a specific translation
> for kernel symbols (__pa_symbol), but other than that it is fairly
> straightforward (except KASAN is being a pain again, but for the purpose of this
> discussion that should not matter too much)
>

With some additional s/__pa/__pa_symbol/ replacements for SMP and KVM,
this runs happily on my Seattle A0 (no kasan yet, though)


> Patch #1 is a fix for a bug that I spotted  while working on this.
>
> Patch #2 introduces the new translations __kimg_to_phys and __pa_symbol. They
> do exactly the same but the former matches the existing __phys_to_kimg, and the
> latter already exists on x86 as well for translating 'symbols visible to C code'
>
> Patch #3 - #9 replace various instances of __pa() translations involving virtual
> addresses pointing into the kernel image.
>
> Patch #10 finally removes the comparison against PAGE_OFFSET from the
> implementation of __virt_to_phys(), so that it can only be used for addresses
> that are known to be in the linear region.
>
> git://git.linaro.org/people/ard.biesheuvel/linux-arm.git arm64-pa-linear-mapping
>
> Ard Biesheuvel (10):
>   arm64: mm: move assignment of 'high_memory' before its first use
>   arm64: introduce __kimg_to_phys() and __pa_symbol()
>   arm64: mm: avoid __pa translations in cpu_replace_ttbr1
>   arm64: mm: avoid __pa translations on empty_zero_page
>   arm64: mm: avoid __pa translations in early_fixmap_init
>   arm64: mm: use __pa_symbol() not __pa() for section boundary symbols
>   arm64: mm: avoid __pa translations for idmap_pg_dir and swapper_pg_dir
>   arm64: vdso: avoid __pa translations
>   arm64: insn: avoid __pa translations
>   arm64: mm: restrict __pa() translations to linear virtual addresses
>
>  arch/arm64/include/asm/memory.h      | 15 ++++++++----
>  arch/arm64/include/asm/mmu_context.h | 10 ++++----
>  arch/arm64/include/asm/pgalloc.h     |  2 --
>  arch/arm64/include/asm/pgtable.h     |  2 +-
>  arch/arm64/kernel/insn.c             |  2 +-
>  arch/arm64/kernel/setup.c            |  8 +++----
>  arch/arm64/kernel/vdso.c             |  5 ++--
>  arch/arm64/mm/init.c                 | 13 +++++++----
>  arch/arm64/mm/mmu.c                  | 24 ++++++++++----------
>  9 files changed, 43 insertions(+), 38 deletions(-)
>
> --
> 2.5.0
>