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Thu, 14 Mar 2019 07:22:35 -0700 (PDT) Received: from localhost.localdomain ([106.215.118.61]) by smtp.gmail.com with ESMTPSA id f65sm23771178pff.21.2019.03.14.07.22.29 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 14 Mar 2019 07:22:34 -0700 (PDT) Subject: Re: [PATCH v2 2/2] crash_core, vmcoreinfo: Append 'MAX_PHYSMEM_BITS' to vmcoreinfo To: Kazuhito Hagio Cc: "linux-kernel@vger.kernel.org" , Boris Petkov , Ingo Molnar , Thomas Gleixner , James Morse , Will Deacon , Michael Ellerman , Paul Mackerras , Benjamin Herrenschmidt , Dave Anderson , "x86@kernel.org" , "linuxppc-dev@lists.ozlabs.org" , "linux-arm-kernel@lists.infradead.org" , "kexec@lists.infradead.org" References: <1552212242-9479-1-git-send-email-bhsharma@redhat.com> <1552212242-9479-3-git-send-email-bhsharma@redhat.com> <4AE2DC15AC0B8543882A74EA0D43DBEC03569E6D@BPXM09GP.gisp.nec.co.jp> From: Bhupesh Sharma Message-ID: <6dac3aec-3f18-de67-f620-aed063986a17@redhat.com> Date: Thu, 14 Mar 2019 19:52:27 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 MIME-Version: 1.0 In-Reply-To: <4AE2DC15AC0B8543882A74EA0D43DBEC03569E6D@BPXM09GP.gisp.nec.co.jp> Content-Type: text/plain; charset=iso-2022-jp; format=flowed; delsp=yes Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Kazu, On 03/13/2019 01:17 AM, Kazuhito Hagio wrote: > Hi Bhupesh, > > -----Original Message----- >> Right now user-space tools like 'makedumpfile' and 'crash' need to rely >> on a best-guess method of determining value of 'MAX_PHYSMEM_BITS' >> supported by underlying kernel. >> >> This value is used in user-space code to calculate the bit-space >> required to store a section for SPARESMEM (similar to the existing >> calculation method used in the kernel implementation): >> >> #define SECTIONS_SHIFT (MAX_PHYSMEM_BITS - SECTION_SIZE_BITS) >> >> Now, regressions have been reported in user-space utilities >> like 'makedumpfile' and 'crash' on arm64, with the recently added >> kernel support for 52-bit physical address space, as there is >> no clear method of determining this value in user-space >> (other than reading kernel CONFIG flags). >> >> As per suggestion from makedumpfile maintainer (Kazu), it makes more >> sense to append 'MAX_PHYSMEM_BITS' to vmcoreinfo in the core code itself >> rather than in arch-specific code, so that the user-space code for other >> archs can also benefit from this addition to the vmcoreinfo and use it >> as a standard way of determining 'SECTIONS_SHIFT' value in user-land. >> >> A reference 'makedumpfile' implementation which reads the >> 'MAX_PHYSMEM_BITS' value from vmcoreinfo in a arch-independent fashion >> is available here: >> >> [0]. https://github.com/bhupesh-sharma/makedumpfile/blob/remove-max-phys-mem-bit-v1/arch/ppc64.c#L471 >> >> Cc: Boris Petkov >> Cc: Ingo Molnar >> Cc: Thomas Gleixner >> Cc: James Morse >> Cc: Will Deacon >> Cc: Michael Ellerman >> Cc: Paul Mackerras >> Cc: Benjamin Herrenschmidt >> Cc: Dave Anderson >> Cc: Kazuhito Hagio >> Cc: x86@kernel.org >> Cc: linuxppc-dev@lists.ozlabs.org >> Cc: linux-arm-kernel@lists.infradead.org >> Cc: linux-kernel@vger.kernel.org >> Cc: kexec@lists.infradead.org >> Signed-off-by: Bhupesh Sharma >> --- >> kernel/crash_core.c | 1 + >> 1 file changed, 1 insertion(+) >> >> diff --git a/kernel/crash_core.c b/kernel/crash_core.c >> index 093c9f917ed0..44b90368e183 100644 >> --- a/kernel/crash_core.c >> +++ b/kernel/crash_core.c >> @@ -467,6 +467,7 @@ static int __init crash_save_vmcoreinfo_init(void) >> #define PAGE_OFFLINE_MAPCOUNT_VALUE (~PG_offline) >> VMCOREINFO_NUMBER(PAGE_OFFLINE_MAPCOUNT_VALUE); >> #endif >> + VMCOREINFO_NUMBER(MAX_PHYSMEM_BITS); > > Some architectures define MAX_PHYSMEM_BITS only with CONFIG_SPARSEMEM, > so we need to move this to the #ifdef section that exports some > mem_section things. > > Thanks! > Kazu Sorry for the late response, I wanted to make sure I check almost all archs to understand if a proposal would work for all. As per my current understanding, we can protect the export of 'MAX_PHYSMEM_BITS' via a #ifdef section against CONFIG_SPARSEMEM, and it should work for all archs. Here are some arguments to support the same, would request maintainers of various archs (in Cc) to correct me if I am missing something here: 1. SPARSEMEM is dependent upon on (!SELECT_MEMORY_MODEL && ARCH_SPARSEMEM_ENABLE) || SPARSEMEM_MANUAL: config SPARSEMEM def_bool y depends on (!SELECT_MEMORY_MODEL && ARCH_SPARSEMEM_ENABLE) || SPARSEMEM_MANUAL 2. For a couple of archs, this option is already turned on by default in their respective defconfigs: $ grep -nrw "CONFIG_SPARSEMEM_MANUAL" * arch/ia64/configs/gensparse_defconfig:18:CONFIG_SPARSEMEM_MANUAL=y arch/powerpc/configs/ppc64e_defconfig:30:CONFIG_SPARSEMEM_MANUAL=y 3. Note that other archs use ARCH_SPARSEMEM_DEFAULT to define if CONFIG_SPARSEMEM_MANUAL is set by default: choice prompt "Memory model" .. default SPARSEMEM_MANUAL if ARCH_SPARSEMEM_DEFAULT 3a. $ grep -nrw -A 2 "ARCH_SPARSEMEM_DEFAULT" * arch/s390/Kconfig:621:config ARCH_SPARSEMEM_DEFAULT arch/s390/Kconfig-622- def_bool y -- arch/x86/Kconfig:1623:config ARCH_SPARSEMEM_DEFAULT arch/x86/Kconfig-1624- def_bool y arch/x86/Kconfig-1625- depends on X86_64 -- arch/powerpc/Kconfig:614:config ARCH_SPARSEMEM_DEFAULT arch/powerpc/Kconfig-615- def_bool y arch/powerpc/Kconfig-616- depends on PPC_BOOK3S_64 -- arch/arm64/Kconfig:850:config ARCH_SPARSEMEM_DEFAULT arch/arm64/Kconfig-851- def_bool ARCH_SPARSEMEM_ENABLE -- arch/sh/mm/Kconfig:138:config ARCH_SPARSEMEM_DEFAULT arch/sh/mm/Kconfig-139- def_bool y -- arch/sparc/Kconfig:315:config ARCH_SPARSEMEM_DEFAULT arch/sparc/Kconfig-316- def_bool y if SPARC64 -- arch/arm/Kconfig:1591:config ARCH_SPARSEMEM_DEFAULT arch/arm/Kconfig-1592- def_bool ARCH_SPARSEMEM_ENABLE Since most archs (except MIPS) set CONFIG_ARCH_SPARSEMEM_DEFAULT/CONFIG_ARCH_SPARSEMEM_ENABLE to y in the default configurations, so even though they don't protect 'MAX_PHYSMEM_BITS' define in CONFIG_SPARSEMEM ifdef sections, we still would be ok protecting the 'MAX_PHYSMEM_BITS' vmcoreinfo export inside a CONFIG_SPARSEMEM ifdef section. Thanks for your inputs, I will include this change in the v3. Regards, Bhupesh