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<351975548.1986001.1578682810951.JavaMail.zimbra@redhat.com> <04287d60-e99e-631b-c134-d6dc39e6a193@redhat.com> <974f3601-25f8-f4e6-43a8-ff4275e9c174@arm.com>

In-Reply-To: MIME-Version: 1.0 X-Mailer: Microsoft Outlook 14.0 Thread-Index: AQGa98r5q5qEPCZDE5DL4GJrrz9qcAGNQyRgApgGah0B/ao0mwIUlx9FAsYr/NkBJYrXxQK1AqgNAhb3920BQkNqpai3DgCQ Date: Wed, 10 Jun 2020 22:17:37 +0530 Message-ID: Subject: RE: Re: [RESEND PATCH v5 2/5] arm64/crash_core: Export TCR_EL1.T1SZ in vmcoreinfo To: Scott Branden , Bhupesh Sharma , Amit Kachhap Content-Type: text/plain; charset="UTF-8" X-Mailman-Approved-At: Thu, 11 Jun 2020 08:06:03 +1000 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: Mark Rutland , Kazuhito Hagio , Ard Biesheuvel , Catalin Marinas , x86@kernel.org, Linux Doc Mailing List , Linux Kernel Mailing List , Ray Jui , linuxppc-dev@lists.ozlabs.org, James Morse , Dave Anderson , bhupesh linux , Will Deacon , kexec mailing list , linux-arm-kernel , Steve Capper Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Hello Bhupesh, V6 patch set on Linux 5.7, did not help. I have applied makedump file http://lists.infradead.org/pipermail/kexec/2019-November/023963.html changes also (makedump-1.6.6). Tried to apply it on makedumpfile 1.6.7. Patch set_2 failed. Would like to know, if you have V5 patch set for makedump file changes. With makedump 1.6.6, able to collect the vmore file. I used latest crash utility (https://www.redhat.com/archives/crash-utility/2019-November/msg00014.html changes are present) When I used crash utility, following is the error: Thanks, -Bharat -----Original Message----- From: Scott Branden [mailto:scott.branden@broadcom.com] Sent: Thursday, April 30, 2020 4:34 AM To: Bhupesh Sharma; Amit Kachhap Cc: Mark Rutland; x86@kernel.org; Will Deacon; Linux Doc Mailing List; Catalin Marinas; Ard Biesheuvel; kexec mailing list; Linux Kernel Mailing List; Kazuhito Hagio; James Morse; Dave Anderson; bhupesh linux; linuxppc-dev@lists.ozlabs.org; linux-arm-kernel; Steve Capper; Ray Jui; Bharat Gooty Subject: Re: Re: [RESEND PATCH v5 2/5] arm64/crash_core: Export TCR_EL1.T1SZ in vmcoreinfo Hi Bhupesh, On 2020-02-23 10:25 p.m., Bhupesh Sharma wrote: > Hi Amit, > > On Fri, Feb 21, 2020 at 2:36 PM Amit Kachhap wrote: >> Hi Bhupesh, >> >> On 1/13/20 5:44 PM, Bhupesh Sharma wrote: >>> Hi James, >>> >>> On 01/11/2020 12:30 AM, Dave Anderson wrote: >>>> ----- Original Message ----- >>>>> Hi Bhupesh, >>>>> >>>>> On 25/12/2019 19:01, Bhupesh Sharma wrote: >>>>>> On 12/12/2019 04:02 PM, James Morse wrote: >>>>>>> On 29/11/2019 19:59, Bhupesh Sharma wrote: >>>>>>>> vabits_actual variable on arm64 indicates the actual VA space size, >>>>>>>> and allows a single binary to support both 48-bit and 52-bit VA >>>>>>>> spaces. >>>>>>>> >>>>>>>> If the ARMv8.2-LVA optional feature is present, and we are running >>>>>>>> with a 64KB page size; then it is possible to use 52-bits of >>>>>>>> address >>>>>>>> space for both userspace and kernel addresses. However, any kernel >>>>>>>> binary that supports 52-bit must also be able to fall back to >>>>>>>> 48-bit >>>>>>>> at early boot time if the hardware feature is not present. >>>>>>>> >>>>>>>> Since TCR_EL1.T1SZ indicates the size offset of the memory region >>>>>>>> addressed by TTBR1_EL1 (and hence can be used for determining the >>>>>>>> vabits_actual value) it makes more sense to export the same in >>>>>>>> vmcoreinfo rather than vabits_actual variable, as the name of the >>>>>>>> variable can change in future kernel versions, but the >>>>>>>> architectural >>>>>>>> constructs like TCR_EL1.T1SZ can be used better to indicate >>>>>>>> intended >>>>>>>> specific fields to user-space. >>>>>>>> >>>>>>>> User-space utilities like makedumpfile and crash-utility, need to >>>>>>>> read/write this value from/to vmcoreinfo >>>>>>> (write?) >>>>>> Yes, also write so that the vmcoreinfo from an (crashing) arm64 >>>>>> system can >>>>>> be used for >>>>>> analysis of the root-cause of panic/crash on say an x86_64 host using >>>>>> utilities like >>>>>> crash-utility/gdb. >>>>> I read this as as "User-space [...] needs to write to vmcoreinfo". >>> That's correct. But for writing to vmcore dump in the kdump kernel, we >>> need to read the symbols from the vmcoreinfo in the primary kernel. >>> >>>>>>>> for determining if a virtual address lies in the linear map range. >>>>>>> I think this is a fragile example. The debugger shouldn't need to >>>>>>> know >>>>>>> this. >>>>>> Well that the current user-space utility design, so I am not sure we >>>>>> can >>>>>> tweak that too much. >>>>>> >>>>>>>> The user-space computation for determining whether an address lies >>>>>>>> in >>>>>>>> the linear map range is the same as we have in kernel-space: >>>>>>>> >>>>>>>> #define __is_lm_address(addr) (!(((u64)addr) & >>>>>>>> BIT(vabits_actual - >>>>>>>> 1))) >>>>>>> This was changed with 14c127c957c1 ("arm64: mm: Flip kernel VA >>>>>>> space"). If >>>>>>> user-space >>>>>>> tools rely on 'knowing' the kernel memory layout, they must have to >>>>>>> constantly be fixed >>>>>>> and updated. This is a poor argument for adding this to something >>>>>>> that >>>>>>> ends up as ABI. >>>>>> See above. The user-space has to rely on some ABI/guaranteed >>>>>> hardware-symbols which can be >>>>>> used for 'determining' the kernel memory layout. >>>>> I disagree. Everything and anything in the kernel will change. The >>>>> ABI rules apply to >>>>> stuff exposed via syscalls and kernel filesystems. It does not apply >>>>> to kernel internals, >>>>> like the memory layout we used yesterday. 14c127c957c1 is a case in >>>>> point. >>>>> >>>>> A debugger trying to rely on this sort of thing would have to play >>>>> catchup whenever it >>>>> changes. >>>> Exactly. That's the whole point. >>>> >>>> The crash utility and makedumpfile are not in the same league as other >>>> user-space tools. >>>> They have always had to "play catchup" precisely because they depend >>>> upon kernel internals, >>>> which constantly change. >>> I agree with you and DaveA here. Software user-space debuggers are >>> dependent on kernel internals (which can change from time-to-time) and >>> will have to play catch-up (which has been the case since the very >>> start). >>> >>> Unfortunately we don't have any clear ABI for software debugging tools - >>> may be something to look for in future. >>> >>> A case in point is gdb/kgdb, which still needs to run with KASLR >>> turned-off (nokaslr) for debugging, as it confuses gdb which resolve >>> kernel symbol address from symbol table of vmlinux. But we can >>> work-around the same in makedumpfile/crash by reading the 'kaslr_offset' >>> value. And I have several users telling me now they cannot use gdb on >>> KASLR enabled kernel to debug panics, but can makedumpfile + crash >>> combination to achieve the same. >>> >>> So, we should be looking to fix these utilities which are broken since >>> the 52-bit changes for arm64. Accordingly, I will try to send the v6 >>> soon while incorporating the comments posted on the v5. >> Any update on the next v6 version. Since this patch series is fixing the >> current broken kdump so need this series to add some more fields in >> vmcoreinfo for Pointer Authentication work. > Sorry for the delay. I was caught up in some other urgent arm64 > user-space issues. > I am preparing the v6 now and hopefully will be able to post it out > for review later today. Did v6 get sent out? > > Thanks, > Bhupesh > > Regards, Scott