linux-kernel - Re: [PATCH v8 6/7] x86: Add support for ZSTD compressed kernel

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Message-ID: <20200724122640.GC632343@gmail.com>
Date:   Fri, 24 Jul 2020 14:26:40 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Nick Terrell <nickrterrell@...il.com>
Cc:     Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, Chris Mason <clm@...com>,
        linux-kbuild@...r.kernel.org, x86@...nel.org,
        gregkh@...uxfoundation.org, Petr Malat <oss@...at.biz>,
        Kees Cook <keescook@...omium.org>,
        Kernel Team <Kernel-team@...com>,
        Adam Borowski <kilobyte@...band.pl>,
        Patrick Williams <patrickw3@...com>, rmikey@...com,
        Patrick Williams <patrick@...cx.xyz>,
        Sedat Dilek <sedat.dilek@...il.com>,
        Norbert Lange <nolange79@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alex Xu <alex_y_xu@...oo.ca>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Nick Terrell <terrelln@...com>
Subject: Re: [PATCH v8 6/7] x86: Add support for ZSTD compressed kernel


* Nick Terrell <nickrterrell@...il.com> wrote:

> --- a/arch/x86/boot/compressed/misc.c
> +++ b/arch/x86/boot/compressed/misc.c
> @@ -12,6 +12,11 @@
>   * High loaded stuff by Hans Lermen & Werner Almesberger, Feb. 1996
>   */
>  
> +/* decompressors bring in EXPORT_SYMBOL which is meaningless and will
> + * cause compiler errors in some cases.
> + */
> +#define __DISABLE_EXPORTS
> +
>  #include "misc.h"
>  #include "error.h"
>  #include "pgtable.h"
> @@ -77,6 +82,10 @@ static int lines, cols;
>  #ifdef CONFIG_KERNEL_LZ4
>  #include "../../../../lib/decompress_unlz4.c"
>  #endif
> +
> +#ifdef CONFIG_KERNEL_ZSTD
> +#include "../../../../lib/decompress_unzstd.c"
> +#endif
>  /*
>   * NOTE: When adding a new decompressor, please update the analysis in
>   * ../header.S.
> diff --git a/arch/x86/include/asm/boot.h b/arch/x86/include/asm/boot.h
> index 680c320363db..d6dd43d25d9f 100644
> --- a/arch/x86/include/asm/boot.h
> +++ b/arch/x86/include/asm/boot.h
> @@ -24,9 +24,11 @@
>  # error "Invalid value for CONFIG_PHYSICAL_ALIGN"
>  #endif
>  
> -#ifdef CONFIG_KERNEL_BZIP2
> +#if defined(CONFIG_KERNEL_BZIP2)
>  # define BOOT_HEAP_SIZE		0x400000
> -#else /* !CONFIG_KERNEL_BZIP2 */
> +#elif defined(CONFIG_KERNEL_ZSTD)
> +# define BOOT_HEAP_SIZE		 0x30000
> +#else
>  # define BOOT_HEAP_SIZE		 0x10000
>  #endif

So the other patches explain why the decompression buffer extra space 
was increased from 64k to 128k, but is there a similar 
calculation/estimate for bumping BOOT_HEAD_SIZE from 64k to 192k?

Admittedly the BZ2 exception doesn't set a good example, but maybe we 
can do this for ZSTD?

Thanks,

	Ingo