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Date:   Tue, 21 Nov 2023 09:50:05 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Ignat Korchagin <ignat@...udflare.com>, eric_devolder@...oo.com
Cc:     linux@...linux.org.uk, catalin.marinas@....com, will@...nel.org,
        chenhuacai@...nel.org, geert@...ux-m68k.org,
        tsbogend@...ha.franken.de,
        James Bottomley <James.Bottomley@...senpartnership.com>,
        deller@....de, ysato@...rs.sourceforge.jp, dalias@...c.org,
        glaubitz@...sik.fu-berlin.de, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        dave.hansen@...ux.intel.com, x86@...nel.org,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-ia64@...r.kernel.org,
        loongarch@...ts.linux.dev, linux-m68k@...ts.linux-m68k.org,
        linux-mips@...r.kernel.org, linux-parisc@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-riscv@...ts.infradead.org,
        linux-s390@...r.kernel.org, linux-sh@...r.kernel.org,
        kernel@...0n.name, mpe@...erman.id.au, npiggin@...il.com,
        christophe.leroy@...roup.eu, paul.walmsley@...ive.com,
        palmer@...belt.com, aou@...s.berkeley.edu, hca@...ux.ibm.com,
        gor@...ux.ibm.com, agordeev@...ux.ibm.com,
        borntraeger@...ux.ibm.com, svens@...ux.ibm.com, hpa@...or.com,
        keescook@...omium.org, paulmck@...nel.org,
        Peter Zijlstra <peterz@...radead.org>, frederic@...nel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Ard Biesheuvel <ardb@...nel.org>, samitolvanen@...gle.com,
        juerg.haefliger@...onical.com, arnd@...db.de,
        rmk+kernel@...linux.org.uk, linus.walleij@...aro.org,
        sebastian.reichel@...labora.com, rppt@...nel.org,
        kirill.shutemov@...ux.intel.com, anshuman.khandual@....com,
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        Greg KH <gregkh@...uxfoundation.org>, tsi@...oix.net,
        hbathini@...ux.ibm.com, sourabhjain@...ux.ibm.com,
        boris.ostrovsky@...cle.com, konrad.wilk@...cle.com,
        kernel-team <kernel-team@...udflare.com>
Subject: Re: Potential config regression after 89cde455 ("kexec: consolidate
 kexec and crash options into kernel/Kconfig.kexec")

Eric DeVolder's Oracle mail address is not available anymore, add his
current mail address he told me. 

On 11/20/23 at 10:52pm, Ignat Korchagin wrote:
> Good day!
> 
> We have recently started to evaluate Linux 6.6 and noticed that we
> cannot disable CONFIG_KEXEC anymore, but keep CONFIG_CRASH_DUMP
> enabled. It seems to be related to commit 89cde455 ("kexec:
> consolidate kexec and crash options into kernel/Kconfig.kexec"), where
> a CONFIG_KEXEC dependency was added to CONFIG_CRASH_DUMP.
> 
> In our current kernel (Linux 6.1) we only enable CONFIG_KEXEC_FILE
> with enforced signature check to support the kernel crash dumping
> functionality and would like to keep CONFIG_KEXEC disabled for
> security reasons [1].
> 
> I was reading the long commit message, but the reason for adding
> CONFIG_KEXEC as a dependency for CONFIG_CRASH_DUMP evaded me. And I
> believe from the implementation perspective CONFIG_KEXEC_FILE should
> suffice here (as we successfully used it for crashdumps on Linux 6.1).
> 
> Is there a reason for adding this dependency or is it just an
> oversight? Would some solution of requiring either CONFIG_KEXEC or
> CONFIG_KEXEC_FILE work here?

I searched the patch history, found Eric didn't add the dependency on
CONFIG_KEXEC at the beginning. Later a linux-next building failure with
randconfig was reported, in there CONFIG_CRASH_DUMP enabled, while
CONFIG_KEXEC is disabled. Finally Eric added the KEXEC dependency for
CRASH_DUMP. Please see below link for more details:

https://lore.kernel.org/all/3e8eecd1-a277-2cfb-690e-5de2eb7b988e@oracle.com/T/#u

And besides, the newly added CONFIG_CRASH_HOTPLUG also needs
CONFIG_KEXEC if the elfcorehdr is allowed to be manipulated when
cpu/memory hotplug hapened.

Thanks
Baoquan

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