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Thu, 23 Nov 2023 03:27:17 -0500 X-MC-Unique: xbU-EiHFNt2UCn3fOV12Bg-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.rdu2.redhat.com [10.11.54.4]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 574DB101A53B; Thu, 23 Nov 2023 08:27:16 +0000 (UTC) Received: from localhost (unknown [10.72.112.97]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 2C8B82026D4C; Thu, 23 Nov 2023 08:27:12 +0000 (UTC) Date: Thu, 23 Nov 2023 16:27:09 +0800 From: Baoquan He To: Ignat Korchagin Subject: Re: Potential config regression after 89cde455 ("kexec: consolidate kexec and crash options into kernel/Kconfig.kexec") Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.4 X-Mailman-Approved-At: Fri, 24 Nov 2023 09:22:20 +1100 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: chenhuacai@kernel.org, linux-ia64@vger.kernel.org, linux-sh@vger.kernel.org, Peter Zijlstra , catalin.marinas@arm.com, linus.walleij@linaro.org, dave.hansen@linux.intel.com, linux-mips@vger.kernel.org, James Bottomley , dalias@libc.org, eric_devolder@yahoo.com, linux-riscv@lists.infradead.org, will@kernel.org, kernel@xen0n.name, tsi@tuyoix.net, linux-s390@vger.kernel.org, agordeev@linux.ibm.com, rmk+kernel@armlinux.org.uk, hpa@zytor.com, paulmck@kernel.org, ysato@users.sourceforge.jp, kernel-team , deller@gmx.de, x86@kernel.org, linux@armlinux.org.uk, paul.walmsley@sifive.com, Ingo Molnar , geert@linux-m68k.org, hbathini@linux.ibm.com, samitolvanen@google.com, ojeda@kernel.org, juerg.haefliger@canonical.com, borntraeger@linux.ibm.com, frederic@kernel.org, arnd@arndb.de, mhiramat@kernel.org, Ard Biesheuvel , thunder.leizhen@huawei.com, aou@eecs.berkeley.edu, keescook@chromium.org, gor@linux.ibm.com, anshuman.khandual@arm.com, hca@linux.ibm.com, xin3.li@intel.com, npiggin@gmail.com, konrad.wilk@oracle.com, linux-m68k@lists.linux-m68k.org, Borislav Petkov , loongarch@lists.linux.dev, glaubitz@physik.fu-berlin.de, Thomas Gleixner , ziy@nvidia.com, linux-arm-kernel@lists.infradead.org, boris.ostrovsky@oracle.com, tsbogend@alpha.franken.de, sebastian.reichel@collabora.com, linux-parisc@vger.kernel.org, Greg KH , kirill.shutemov@linux.intel.com, ndesaulniers@google.com, linux-kernel , sourabhjain@linux.ibm.com, palmer@dabbelt.com, svens@linux.ibm.com, tj@kernel.org, Andrew Morton , linuxppc-dev@lists.ozlabs.org, masahiroy@kernel.org, rppt@kernel.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On 11/22/23 at 09:47am, Ignat Korchagin wrote: > On Wed, Nov 22, 2023 at 9:34 AM Baoquan He wrote: > > > > On 11/21/23 at 09:43am, Ignat Korchagin wrote: > > > On Tue, Nov 21, 2023 at 7:53 AM Ignat Korchagin wrote: > > > > > > > > On Tue, Nov 21, 2023 at 1:50 AM Baoquan He wrote: > > > > > > > > > > Eric DeVolder's Oracle mail address is not available anymore, add his > > > > > current mail address he told me. > > > > > > > > Thank you! > > > > > > > > > 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 > > > > > > > > Thank you for digging this up. However I'm still confused, because > > > > this is exactly how we configure Linux 6.1 (although we do have > > > > CONFIG_KEXEC_FILE enabled) and we don't have any problems. I believe > > > > we did not investigate this issue properly. > > > > > > I did some preliminary investigation for this. If I patch out the > > > dependency on CONFIG_KEXEC the kernel builds just fine for x86 > > > (without CONFIG_CRASH_HOTPLUG - which is probably another issue) - so > > > this was the previous behaviour. I can see that the reported error is > > > for arm architecture and was able to reproduce it with a simple cross > > > compiler in Debian. However, I think it is still somehow related to > > > this patchset as the previous kernels (up to 6.5) build fine with just > > > CONFIG_CRASH_DUMP and without CONFIG_KEXEC for arm as well. So even > > > for arm it was introduced in 6.6. > > > > Thanks for the information. > > > > I haven't run the reproducer of issue reported on Eric's old patchset, > > while checkout to kernel 6.1, only s390 selected KEXEC for CRASH_DUMP > > already. And with the ARM building breakage, the simplest idea is > > to select KEXEC only for ARM or S390 CRASH_DUMP. I plan to try the > > reproducer later. If you have any idea or draft patch, please feel free > > to post. > > The thing is - before 6.6 even ARM did not require KEXEC for > CRASH_DUMP (at least to successfully compile), so I think we should > understand what changed first before adding a dependency for ARM. I'll > try to investigate more, if I have time. I did a cross compiling of arm on x86_64, it clearly requires KEXEC for CRASH_DUMP if the select of KEXEC for CRASH_DUMP is removed and CONFIG_KEXEC=n is set. 1) building error, only copy the first one: ========================================== In file included from ../include/linux/ima.h:13, from ../security/keys/key.c:16: ../include/linux/kexec.h:38:2: error: #error KEXEC_SOURCE_MEMORY_LIMIT not defined 38 | #error KEXEC_SOURCE_MEMORY_LIMIT not defined | ^~~~~ ../include/linux/kexec.h:42:2: error: #error KEXEC_DESTINATION_MEMORY_LIMIT not defined 42 | #error KEXEC_DESTINATION_MEMORY_LIMIT not defined | ^~~~~ ../include/linux/kexec.h:46:2: error: #error KEXEC_CONTROL_MEMORY_LIMIT not defined 46 | #error KEXEC_CONTROL_MEMORY_LIMIT not defined | ^~~~~ ../include/linux/kexec.h:54:2: error: #error KEXEC_CONTROL_PAGE_SIZE not defined 54 | #error KEXEC_CONTROL_PAGE_SIZE not defined | ^~~~~ ../include/linux/kexec.h:58:2: error: #error KEXEC_ARCH not defined 58 | #error KEXEC_ARCH not defined | ^~~~~ In file included from ../drivers/misc/pvpanic/pvpanic.c:13: 2) Kconfig items I enabled: ==== CONFIG_CRASH_CORE=y CONFIG_KEXEC_CORE=y # CONFIG_KEXEC is not set CONFIG_CRASH_DUMP=y 3) KEXEC select is dropped so as not to enable KEXEC automatically: ===== diff --git a/kernel/Kconfig.kexec b/kernel/Kconfig.kexec index 7aff28ded2f4..1cc3b1c595d7 100644 --- a/kernel/Kconfig.kexec +++ b/kernel/Kconfig.kexec @@ -97,7 +97,6 @@ config CRASH_DUMP depends on ARCH_SUPPORTS_KEXEC select CRASH_CORE select KEXEC_CORE - select KEXEC help Generate crash dump after being started by kexec. This should be normally only set in special crash dump kernels > > > diff --git a/kernel/Kconfig.kexec b/kernel/Kconfig.kexec > > index 7aff28ded2f4..382dcd8d7a9d 100644 > > --- a/kernel/Kconfig.kexec > > +++ b/kernel/Kconfig.kexec > > @@ -97,7 +97,7 @@ config CRASH_DUMP > > depends on ARCH_SUPPORTS_KEXEC > > select CRASH_CORE > > select KEXEC_CORE > > - select KEXEC > > + select KEXEC if (ARM || S390) > > > > > > arch/s390/Kconfig in kernel 6.1: > > config CRASH_DUMP > > bool "kernel crash dumps" > > select KEXEC > > help > > Generate crash dump after being started by kexec. > > Crash dump kernels are loaded in the main kernel with kexec-tools > > into a specially reserved region and then later executed after > > a crash by kdump/kexec. > > Refer to for more details on this. > > This option also enables s390 zfcpdump. > > See also > > > > > > > > > > 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. > > > > > > > > This still feels like a regression to me: any crash dump support > > > > should be independent of KEXEC syscalls being present. While probably > > > > the common case (including us) that the crashing kernel and recovery > > > > kernel are the same, they don't have to be. We need kexec syscall in > > > > the crashing kernel, but crashdump support in the recovery kernel (but > > > > the recovery kernel not having the kexec syscalls should be totally > > > > fine). If we do require some code definitions from kexec - at most we > > > > should put them under CONFIG_KEXEC_CORE. > > > > > > > > > Thanks > > > > > Baoquan > > > > > > > > > > > Ignat > > > > > >