From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mail-pf1-f194.google.com ([209.85.210.194]) by bombadil.infradead.org with esmtps (Exim 4.90_1 #2 (Red Hat Linux)) id 1gtQI4-0007je-3w for kexec@lists.infradead.org; Tue, 12 Feb 2019 05:07:29 +0000 Received: by mail-pf1-f194.google.com with SMTP id j3so689529pfi.12 for ; Mon, 11 Feb 2019 21:07:27 -0800 (PST) Subject: Re: [PATCH] arm64, vmcoreinfo : Append 'MAX_USER_VA_BITS' and 'MAX_PHYSMEM_BITS' to vmcoreinfo References: <1548850991-11879-1-git-send-email-bhsharma@redhat.com> <20190131014800.GB15785@dhcp-128-65.nay.redhat.com> <4AE2DC15AC0B8543882A74EA0D43DBEC03567AA3@BPXM09GP.gisp.nec.co.jp> From: Bhupesh Sharma Message-ID: Date: Tue, 12 Feb 2019 10:37:19 +0530 MIME-Version: 1.0 In-Reply-To: <4AE2DC15AC0B8543882A74EA0D43DBEC03567AA3@BPXM09GP.gisp.nec.co.jp> Content-Language: en-US List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed"; DelSp="yes" Sender: "kexec" Errors-To: kexec-bounces+dwmw2=infradead.org@lists.infradead.org To: Kazuhito Hagio , Dave Young Cc: Mark Rutland , "lijiang@redhat.com" , "bhe@redhat.com" , "ard.biesheuvel@linaro.org" , "catalin.marinas@arm.com" , "kexec@lists.infradead.org" , Will Deacon , AKASHI Takahiro , James Morse , Borislav Petkov , "anderson@redhat.com" , "linux-arm-kernel@lists.infradead.org" Hi Kazu, On 02/04/2019 09:34 PM, Kazuhito Hagio wrote: > On 1/30/2019 8:48 PM, Dave Young wrote: >> + more people >> On 01/30/19 at 05:53pm, Bhupesh Sharma wrote: >>> With ARMv8.2-LVA and LPA architecture extensions, arm64 hardware which >>> supports these extensions can support upto 52-bit virtual and 52-bit >>> physical addresses respectively. >>> >>> Since at the moment we enable the support of these extensions via CONFIG >>> flags, e.g. >>> - LPA via CONFIG_ARM64_PA_BITS_52 >>> >>> there are no clear mechanisms in user-space right now to >>> deteremine these CONFIG flag values and also determine the PARange and >>> VARange address values. >>> >>> User-space tools like 'makedumpfile' and 'crash-utility' can instead >>> use the 'MAX_USER_VA_BITS' and 'MAX_PHYSMEM_BITS' values to determine >>> the maximum virtual address and physical address (respectively) >>> supported by underlying kernel. >>> >>> A reference 'makedumpfile' implementation which uses this approach to >>> determining the maximum physical address is available in [0]. >>> >>> [0]. >> https://github.com/bhupesh-sharma/makedumpfile/blob/52-bit-pa-support-via-vmcore-v1/arch/arm64.c#L490 >> >> I'm not objecting the patch, just want to make sure to make clear about >> things and make sure these issues are aware by people, and leave arm >> people to review the arm bits. >> >> 1. MAX_PHYSMEM_BITS >> As we previously found, back to 2014 makedumpfile took a patch to read the >> value from vmcore but the kernel patch was not accepted. >> So we should first make clear if this is really needed, why other arches >> do not need this in makedumpfile. >> >> If we really need it then should it be arm64 only? >> >> If it is arm64 only then the makedumpfile code should read this number >> only for arm64. > > Sorry for the delay. > > According to the kernel patch, some of arm32 platforms may need it > http://lists.infradead.org/pipermail/kexec/2014-May/011909.html > but except for them (and arm64), makedumpfile can manage with kernel > version and some switches to determine this value so far. > >> >> Also Lianbo added the vmcoreinfo documents, I believe it stays in -tip >> tree, need to make sure to document this as well. >> >> 2. MAX_USER_VA_BITS >> Does makedumpfile care about userspace VA bits? I do not see other code >> doing this, Kazu and Dave A should be able to comment. > > The mapping makedumpfile uses on arm64 is swapper_pg_dir only, so > unless the config affects its structure or something, makedumpfile > will not need this value. I captured this case in more details while sending out the makedumpfile enablement patch for ARMv8.2-LVA (see [0]), but here is a brief summary on the same: Since at the moment we enable the support of the ARMv8.2-LVA extension for 52-bit user-space VA in the kernel via a CONFIG flags (CONFIG_ARM64_USER_VA_BITS_52), so there are no clear mechanisms in user-space to determine this CONFIG flag value and use it to determine the address range values. Since 'VA_BITS' are already exported via vmcoreinfo, if we export 'MAX_USER_VA_BITS' as well, we can use the same in user-space to check if the 'MAX_USER_VA_BITS' value is greater than 'VA_BITS'. If yes, then we are running a use-case where user-space is 52-bit while the underlying kernel is still 48-bit. The increased 'PTRS_PER_PGD' value for such cases needs to be then calculated as is done by the underlying kernel (see 'arch/arm64/include/asm/pgtable-hwdef.h' for details): #define PTRS_PER_PGD (1 << (MAX_USER_VA_BITS - PGDIR_SHIFT)) Also, note that 'arch/arm64/include/asm/memory.h' defines 'MAX_USER_VA_BITS' as 'VA_BITS' in case 'CONFIG_ARM64_USER_VA_BITS_52' is set to 'n': #ifdef CONFIG_ARM64_USER_VA_BITS_52 #define MAX_USER_VA_BITS 52 #else #define MAX_USER_VA_BITS VA_BITS #endif So, makedumpfile will need this symbol exported in vmcore to make the above determination. [0]. http://lists.infradead.org/pipermail/kexec/2019-February/022425.html Thanks, Bhupesh _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec