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Date:   Wed, 5 Jul 2023 10:22:52 -0500
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Subject: Re: [PATCH v4 03/13] arm/kexec: refactor for kernel/Kconfig.kexec
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To:     Arnd Bergmann <arnd@arndb.de>,
        Russell King <linux@armlinux.org.uk>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Huacai Chen <chenhuacai@kernel.org>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        "James E . J . Bottomley" <James.Bottomley@HansenPartnership.com>,
        Helge Deller <deller@gmx.de>,
        Yoshinori Sato <ysato@users.sourceforge.jp>,
        Rich Felker <dalias@libc.org>,
        John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-ia64@vger.kernel.org, loongarch@lists.linux.dev,
        linux-m68k@lists.linux-m68k.org, linux-mips@vger.kernel.org,
        linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
        linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org,
        linux-sh@vger.kernel.org
Cc:     WANG Xuerui <kernel@xen0n.name>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Nicholas Piggin <npiggin@gmail.com>,
        Christophe Leroy <christophe.leroy@csgroup.eu>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Heiko Carstens <hca@linux.ibm.com>, gor@linux.ibm.com,
        Alexander Gordeev <agordeev@linux.ibm.com>,
        borntraeger@linux.ibm.com, Sven Schnelle <svens@linux.ibm.com>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Kees Cook <keescook@chromium.org>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Frederic Weisbecker <frederic@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Ard Biesheuvel <ardb@kernel.org>,
        Sami Tolvanen <samitolvanen@google.com>,
        Juerg Haefliger <juerg.haefliger@canonical.com>,
        Russell King <rmk+kernel@armlinux.org.uk>,
        Linus Walleij <linus.walleij@linaro.org>,
        Sebastian Reichel <sebastian.reichel@collabora.com>,
        Mike Rapoport <rppt@kernel.org>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Anshuman Khandual <anshuman.khandual@arm.com>,
        Zi Yan <ziy@nvidia.com>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Miguel Ojeda <ojeda@kernel.org>,
        Zhen Lei <thunder.leizhen@huawei.com>,
        Xin Li <xin3.li@intel.com>, Tejun Heo <tj@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        tsi@tuyoix.net, Baoquan He <bhe@redhat.com>,
        hbathini@linux.ibm.com, sourabhjain@linux.ibm.com,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
References: <20230705142004.3605799-1-eric.devolder@oracle.com>
 <20230705142004.3605799-4-eric.devolder@oracle.com>
 <09f70de6-9409-4fa4-b9ea-831078d914e7@app.fastmail.com>
From:   Eric DeVolder <eric.devolder@oracle.com>
In-Reply-To: <09f70de6-9409-4fa4-b9ea-831078d914e7@app.fastmail.com>
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On 7/5/23 10:05, Arnd Bergmann wrote:
> On Wed, Jul 5, 2023, at 16:19, Eric DeVolder wrote:
>> The kexec and crash kernel options are provided in the common
>> kernel/Kconfig.kexec. Utilize the common options and provide
>> the ARCH_SUPPORTS_ and ARCH_SELECTS_ entries to recreate the
>> equivalent set of KEXEC and CRASH options.
>>
>> Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>
> 
>> +config ARCH_SUPPORTS_KEXEC
>> +	def_bool (!SMP || PM_SLEEP_SMP) && MMU
>>
>>   config ATAGS_PROC
>>   	bool "Export atags in procfs"
>> @@ -1668,17 +1656,8 @@ config ATAGS_PROC
>>   	  Should the atags used to boot the kernel be exported in an "atags"
>>   	  file in procfs. Useful with kexec.
>>
>> -config CRASH_DUMP
>> -	bool "Build kdump crash kernel (EXPERIMENTAL)"
>> -	help
>> -	  Generate crash dump after being started by kexec. This should
>> -	  be normally only set in special crash dump kernels which are
>> -	  loaded in the main kernel with kexec-tools into a specially
>> -	  reserved region and then later executed after a crash by
>> -	  kdump/kexec. The crash dump kernel must be compiled to a
>> -	  memory address not used by the main kernel
>> -
>> -	  For more details see Documentation/admin-guide/kdump/kdump.rst
>> +config ARCH_SUPPORTS_CRASH_DUMP
>> +	def_bool y
>>
> 
> I see this is now in linux-next, and it caused a few randconfig
> build issues, these never happened in the past:

Arnd,
Thanks for looking at this!

I received randconfig errors from Andrew Morton's machinery. When investigating I
found that randconfig was able to specify CRASH_DUMP without KEXEC, and that lead
to problems. I believe this situation existed prior to this series as well.
Specifically CRASH_DUMP does not have a dependency on KEXEC, or select (only s390
has this hole closed).

For CRASH_DUMP, this series now selects KEXEC to close this gap, which is what a
sane config would have (ie both CRASH_DUMP and KEXEC).

Do you think the changes outlined below are still needed?
eric


> 
> * The #ifdef CONFIG_KEXEC check in arch/arm/include/asm/kexec.h
>    needs to be changed to CONFIG_KEXEC_CORE:
> 
> include/linux/kexec.h:41:2: error: #error KEXEC_SOURCE_MEMORY_LIMIT not defined
> 
>    same thing on m68k
> 
> * ARCH_SUPPORTS_CRASH_DUMP needs the same dependency as ARCH_SUPPORTS_KEXEC,
>    otherwise we seem to run into an obscure assembler error building the kdump
>    core on architectures that do not support kdump:
> 
>    /tmp/ccpYl6w9.s:1546: Error: selected processor does not support requested special purpose register -- `mrs r2,cpsr'
> 
> * Most architectures build machine_kexec.o only when KEXEC is enabled,
>    this also needs to be changed to KEXEC_CORE:
> 
> --- a/arch/arm/kernel/Makefile
> +++ b/arch/arm/kernel/Makefile
> @@ -59,7 +59,7 @@ obj-$(CONFIG_FUNCTION_TRACER) += entry-ftrace.o
>   obj-$(CONFIG_DYNAMIC_FTRACE)   += ftrace.o insn.o patch.o
>   obj-$(CONFIG_FUNCTION_GRAPH_TRACER)    += ftrace.o insn.o patch.o
>   obj-$(CONFIG_JUMP_LABEL)       += jump_label.o insn.o patch.o
> -obj-$(CONFIG_KEXEC)            += machine_kexec.o relocate_kernel.o
> +obj-$(CONFIG_KEXEC_CORE)       += machine_kexec.o relocate_kernel.o
>   # Main staffs in KPROBES are in arch/arm/probes/ .
>   obj-$(CONFIG_KPROBES)          += patch.o insn.o
>   obj-$(CONFIG_OABI_COMPAT)      += sys_oabi-compat.o
> 
> 
>     Arnd