linux-kernel - Re: [PATCH] Use CRC32 and a 1MiB dictionary for XZ compressed modules

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Date:   Fri, 22 Sep 2023 22:34:30 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Martin Nybo Andersen <tweek@...ek.dk>
Cc:     Tor Vic <torvic9@...lbox.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nicolas Schier <nicolas@...sle.eu>,
        Nick Terrell <terrelln@...com>, linux-kbuild@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Lucas De Marchi <lucas.de.marchi@...il.com>
Subject: Re: [PATCH] Use CRC32 and a 1MiB dictionary for XZ compressed modules

On Fri, Sep 22, 2023 at 8:04 PM Martin Nybo Andersen <tweek@...ek.dk> wrote:
>
>
> On Fri, 22 Sep 2023, Masahiro Yamada wrote:
>
> [...]
>
> > Hello, sorry for the delay.
> >
> > I am OK with picking the patch to my tree.
>
> Hi,
>
> That sound great :)
>
> > I think we can use --check=crc32 --lzma2=dict=1MiB
> > unconditionally.
> >
> > (But, if the in-kernel decompressor is improved
> > to understand CRC64 in the future, we can loosen
> > this restriction again.)
>
> Of course.
>
> > Just small change requests.
> >
> > Please do not use the Fixes tag to point at the Debian bug tracker.
> >
> >
> > Instead, you can do
> >
> > Link: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1050582
> >
> >   or
> >
> > Closes: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1050582
> >
> >
> >
> > Also, mention that this change happened in
> >
> > kmod commit 09c9f8c5df04 ("libkmod: Use kernel decompression when available")
> >
> > in the commit description might be helpful.
> >
> >
> >
> >
> > I added Lukas to CC.
> > He is the author of the change on kmod side.
>
> Is this ok?


Yes, perfect!

Thanks.


>
> Kmod is now (since kmod commit 09c9f8c5df04 ("libkmod: Use kernel
> decompression when available")) using the kernel decompressor, when
> loading compressed modules.
>
> However, the kernel XZ decompressor is XZ Embedded, which doesn't
> handle CRC64 and dictionaries larger than 1MiB.
>
> Use CRC32 and 1MiB dictionary when XZ compressing and installing
> kernel modules.
>
> Link: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1050582
> Signed-off-by: Martin Nybo Andersen <tweek@...ek.dk>
> ---
>   scripts/Makefile.modinst | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/scripts/Makefile.modinst b/scripts/Makefile.modinst
> index c59cc57286ba..ffbafbd3aeea 100644
> --- a/scripts/Makefile.modinst
> +++ b/scripts/Makefile.modinst
> @@ -144,7 +144,7 @@ endif
>   quiet_cmd_gzip = GZIP    $@
>         cmd_gzip = $(KGZIP) -n -f $<
>   quiet_cmd_xz = XZ      $@
> -      cmd_xz = $(XZ) --lzma2=dict=2MiB -f $<
> +      cmd_xz = $(XZ) --check=crc32 --lzma2=dict=1MiB -f $<
>   quiet_cmd_zstd = ZSTD    $@
>         cmd_zstd = $(ZSTD) -T0 --rm -f -q $<
> --
> 2.40.1



-- 
Best Regards
Masahiro Yamada