linux-kernel - Re: [PATCH v3] LoongArch: Add support to clone a time namespace

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Date:   Wed, 31 May 2023 16:34:06 +0800
From:   Youling Tang <tangyouling@...ngson.cn>
To:     Tiezhu Yang <yangtiezhu@...ngson.cn>
Cc:     Huacai Chen <chenhuacai@...nel.org>,
        WANG Xuerui <kernel@...0n.name>,
        Christian Brauner <brauner@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org,
        loongson-kernel@...ts.loongnix.cn
Subject: Re: [PATCH v3] LoongArch: Add support to clone a time namespace

Hi, Tiezhu

On 05/31/2023 03:56 PM, Tiezhu Yang wrote:
/* snip */
> diff --git a/arch/loongarch/include/asm/vdso/vdso.h b/arch/loongarch/include/asm/vdso/vdso.h
> index 3b55d32..fa6049e 100644
> --- a/arch/loongarch/include/asm/vdso/vdso.h
> +++ b/arch/loongarch/include/asm/vdso/vdso.h
> @@ -16,10 +16,31 @@ struct vdso_pcpu_data {
>
>  struct loongarch_vdso_data {
>  	struct vdso_pcpu_data pdata[NR_CPUS];
> -	struct vdso_data data[CS_BASES]; /* Arch-independent data */
>  };
>
> -#define VDSO_DATA_SIZE PAGE_ALIGN(sizeof(struct loongarch_vdso_data))
> +/*
> + * The layout of vvar:
> + *
> + *                      high
> + * +---------------------+--------------------------+
> + * | loongarch vdso data | LOONGARCH_VDSO_DATA_SIZE |
> + * +---------------------+--------------------------+
> + * | timens vdso data    | PAGE_SIZE                |
> + * +---------------------+--------------------------+
> + * | generic vdso data   | PAGE_SIZE                |
> + * +---------------------+--------------------------+
> + *                      low
> + */
> +#define LOONGARCH_VDSO_DATA_SIZE PAGE_ALIGN(sizeof(struct loongarch_vdso_data))
> +#define LOONGARCH_VDSO_DATA_PAGES (LOONGARCH_VDSO_DATA_SIZE >> PAGE_SHIFT)

> +#define VVAR_SIZE (VVAR_LOONGARCH_PAGES_START * PAGE_SIZE + LOONGARCH_VDSO_DATA_SIZE)
> +
> +enum vvar_pages {
> +	VVAR_GENERIC_PAGE_OFFSET,
> +	VVAR_TIMENS_PAGE_OFFSET,
> +	VVAR_LOONGARCH_PAGES_START,
> +	VVAR_LOONGARCH_PAGES_END = VVAR_LOONGARCH_PAGES_START + LOONGARCH_VDSO_DATA_PAGES - 1,
> +};
It can also be changed as follows,

enum vvar_pages {
	VVAR_GENERIC_PAGE_OFFSET,
	VVAR_TIMENS_PAGE_OFFSET,
	VVAR_LOONGARCH_PAGES_START,
	VVAR_LOONGARCH_PAGES_END = VVAR_LOONGARCH_PAGES_START + 
LOONGARCH_VDSO_DATA_PAGES - 1,
	VVAR_NR_PAGES,
};

#define VVAR_SIZE (VVAR_NR_PAGES << PAGE_SHIFT)

Which do you think is better?

Youling.