linux-kernel - Re: [PATCH] riscv: Fixup one-page wasting

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Date:   Wed, 24 Nov 2021 12:25:14 +0530
From:   Anup Patel <anup@...infault.org>
To:     Guo Ren <guoren@...nel.org>
Cc:     "linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        linux-csky@...r.kernel.org, Guo Ren <guoren@...ux.alibaba.com>,
        Alexandre Ghiti <alex@...ti.fr>,
        Atish Patra <Atish.Patra@....com>
Subject: Re: [PATCH] riscv: Fixup one-page wasting

On Wed, Nov 24, 2021 at 11:35 AM <guoren@...nel.org> wrote:
>
> From: Guo Ren <guoren@...ux.alibaba.com>
>
> For small memory systems(Allwinner D1s/F133), one page size memory
> cannot be ignored.
>
> Signed-off-by: Guo Ren <guoren@...ux.alibaba.com>
> Cc: Alexandre Ghiti <alex@...ti.fr>
> Cc: Anup Patel <anup@...infault.org>
> Cc: Atish Patra <Atish.Patra@....com>

This PATCH breaks the CPU hotplug functionality.

When a CPU/HART is turned off and turned on at runtime, the
low-level relocate() will be called to enable MMU on the CPU
being brought-up which in-turn uses trampoline_pg_dir.

Regards,
Anup

> ---
>  arch/riscv/mm/init.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index 24b2b8044602..097bb3bc4020 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -241,9 +241,9 @@ unsigned long riscv_pfn_base __ro_after_init;
>  EXPORT_SYMBOL(riscv_pfn_base);
>
>  pgd_t swapper_pg_dir[PTRS_PER_PGD] __page_aligned_bss;
> -pgd_t trampoline_pg_dir[PTRS_PER_PGD] __page_aligned_bss;
>  static pte_t fixmap_pte[PTRS_PER_PTE] __page_aligned_bss;
>
> +pgd_t trampoline_pg_dir[PTRS_PER_PGD] __initdata __aligned(PAGE_SIZE);
>  pgd_t early_pg_dir[PTRS_PER_PGD] __initdata __aligned(PAGE_SIZE);
>  static pmd_t __maybe_unused early_dtb_pmd[PTRS_PER_PMD] __initdata __aligned(PAGE_SIZE);
>
> --
> 2.25.1
>