linux-kernel - Re: PROBLEM: zstd bzImage decompression fails for some x86

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Message-ID: <74757C2A-7C09-4C2E-9828-E8D12EE4706B@fb.com>
Date:   Mon, 28 Sep 2020 18:02:03 +0000
From:   Nick Terrell <terrelln@...com>
To:     Feng Tang <feng.tang@...el.com>
CC:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        X86 ML <x86@...nel.org>, Sedat Dilek <sedat.dilek@...il.com>,
        Ingo Molnar <mingo@...nel.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        "linux-kbuild@...r.kernel.org" <linux-kbuild@...r.kernel.org>,
        "rong.a.chen@...el.com" <rong.a.chen@...el.com>,
        "philip.li@...el.com" <philip.li@...el.com>
Subject: Re: PROBLEM: zstd bzImage decompression fails for some x86_32 config
 on 5.9-rc1



> On Sep 28, 2020, at 1:55 AM, Feng Tang <feng.tang@...el.com> wrote:
> 
> Hi Nick,
> 
> 0day has found some kernel decomprssion failure case since 5.9-rc1 (X86_32
> build), and it could be related with ZSTD code, though initially we bisected
> to some other commits.
> 
> The error messages are: 
> 	
> 	early console in setup code
> 	Wrong EFI loader signature.
> 	early console in extract_kernel
> 	input_data: 0x046f50b4
> 	input_len: 0x01ebbeb6
> 	output: 0x01000000
> 	output_len: 0x04fc535c
> 	kernel_total_size: 0x055f5000
> 	needed_size: 0x055f5000
> 	
> 	Decompressing Linux...
> 	
> 	ZSTD-compressed data is corrupt
> 
> This could be reproduced by compiling the kernel with attached config,
> and use QEMU to boot it.
> 
> We suspect it could be related with the kernel size, as we only see
> it on big kernel, and some more info are:
> 
> * If we remove a lot of kernel config to build a much smaller kernel,
>  it will boot fine
> 
> * If we change the zstd algorithm from zstd22 to zstd19, the kernel will
>  boot fine with below patch
> 
> 	diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
> 	index 3962f59..8fe71ba 100644
> 	--- a/arch/x86/boot/compressed/Makefile
> 	+++ b/arch/x86/boot/compressed/Makefile
> 	@@ -147,7 +147,7 @@ $(obj)/vmlinux.bin.lzo: $(vmlinux.bin.all-y) FORCE
> 	 $(obj)/vmlinux.bin.zst: $(vmlinux.bin.all-y) FORCE
> 	-	$(call if_changed,zstd22)
> 	+	$(call if_changed,zstd)
> 
> 
> Please let me know if you need more info, and sorry for the late report
> as we just tracked down to this point.

Thanks for the report, I will look into it today.

Best,
Nick

> Thanks,
> Feng
> 
> 
> 
> <zstd_x86_32.config>