linux-kernel - Re: [PATCH v2 00/10] Independent per-CPU data section for nVHE

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Message-ID: <20200916123913.GA28056@willie-the-truck>
Date:   Wed, 16 Sep 2020 13:39:14 +0100
From:   Will Deacon <will@...nel.org>
To:     David Brazdil <dbrazdil@...gle.com>
Cc:     Marc Zyngier <maz@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Dennis Zhou <dennis@...nel.org>, Tejun Heo <tj@...nel.org>,
        Christoph Lameter <cl@...ux.com>,
        Arnd Bergmann <arnd@...db.de>,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kvmarm@...ts.cs.columbia.edu, linux-arch@...r.kernel.org,
        kernel-team@...roid.com
Subject: Re: [PATCH v2 00/10] Independent per-CPU data section for nVHE

On Wed, Sep 16, 2020 at 01:24:12PM +0100, David Brazdil wrote:
> > I was also wondering about another approach - using the PERCPU_SECTION macro
> > unchanged in the hyp linker script. It would lay out a single .data..percpu and
> > we would then prefix it with .hyp and the symbols with __kvm_nvhe_ as with
> > everything else. WDYT? Haven't tried that yet, could be a naive idea. 
> 
> Seems to work. Can't use PERCPU_SECTION directly because then we couldn't
> rename it in the same linker script, but if we just unwrap that one layer
> we can use PERCPU_INPUT. No global macro changes needed.
> 
> Let me know what you think.
> 
> ------8<------
> diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
> index 5904a4de9f40..9e6bf21268f1 100644
> --- a/arch/arm64/kernel/vmlinux.lds.S
> +++ b/arch/arm64/kernel/vmlinux.lds.S
> @@ -195,11 +195,9 @@ SECTIONS
>         PERCPU_SECTION(L1_CACHE_BYTES)
> 
>         /* KVM nVHE per-cpu section */
> -       #undef PERCPU_SECTION_NAME
> -       #undef PERCPU_SYMBOL_NAME
> -       #define PERCPU_SECTION_NAME(suffix)     CONCAT3(.hyp, PERCPU_SECTION_BASE_NAME, suffix)
> -       #define PERCPU_SYMBOL_NAME(name)        __kvm_nvhe_ ## name
> -       PERCPU_SECTION(L1_CACHE_BYTES)
> +       . = ALIGN(PAGE_SIZE);
> +       .hyp.data..percpu : { *(.hyp.data..percpu) }
> +       . = ALIGN(PAGE_SIZE);
> 
>         .rela.dyn : ALIGN(8) {
>                 *(.rela .rela*)
> diff --git a/arch/arm64/kvm/hyp/nvhe/hyp.lds.S b/arch/arm64/kvm/hyp/nvhe/hyp.lds.S
> index 7d8c3fa004f4..1d8e4f7edc29 100644
> --- a/arch/arm64/kvm/hyp/nvhe/hyp.lds.S
> +++ b/arch/arm64/kvm/hyp/nvhe/hyp.lds.S
> @@ -4,6 +4,10 @@
>   * Written by David Brazdil <dbrazdil@...gle.com>
>   */
> 
> +#include <asm-generic/vmlinux.lds.h>
> +#include <asm/cache.h>
> +#include <asm/memory.h>
> +
>  /*
>   * Defines an ELF hyp section from input section @NAME and its subsections.
>   */
> @@ -11,9 +15,9 @@
> 
>  SECTIONS {
>         HYP_SECTION(.text)
> -       HYP_SECTION(.data..percpu)
> -       HYP_SECTION(.data..percpu..first)
> -       HYP_SECTION(.data..percpu..page_aligned)
> -       HYP_SECTION(.data..percpu..read_mostly)
> -       HYP_SECTION(.data..percpu..shared_aligned)
> +
> +       .hyp..data..percpu : {

Too many '.'s here?

> +               __per_cpu_load = .;

I don't think we need this symbol.

Otherwise, idea looks good to me. Can you respin like this, but also
incorporating some of the cleanup in the diff I posted, please?

Will