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Wed, 25 Dec 2019 10:49:43 -0800 (PST) Received: from localhost.localdomain ([122.177.237.105]) by smtp.gmail.com with ESMTPSA id b98sm7539818pjc.16.2019.12.25.10.49.38 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 25 Dec 2019 10:49:42 -0800 (PST) Subject: Re: [RESEND PATCH v5 5/5] Documentation/vmcoreinfo: Add documentation for 'TCR_EL1.T1SZ' To: James Morse , linux-kernel@vger.kernel.org References: <1575057559-25496-1-git-send-email-bhsharma@redhat.com> <1575057559-25496-6-git-send-email-bhsharma@redhat.com> <8a982138-f1fa-34e8-18fd-49a79cea3652@arm.com> From: Bhupesh Sharma Message-ID: Date: Thu, 26 Dec 2019 00:19:35 +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: <8a982138-f1fa-34e8-18fd-49a79cea3652@arm.com> Content-Language: en-US X-MC-Unique: hRBEEhQYMW-JwD8u7lhkYw-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit 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 , Ard Biesheuvel , linux-doc@vger.kernel.org, Will Deacon , x86@kernel.org, kexec@lists.infradead.org, Kazuhito Hagio , Dave Anderson , Catalin Marinas , bhupesh.linux@gmail.com, linuxppc-dev@lists.ozlabs.org, linux-arm-kernel@lists.infradead.org, Steve Capper Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Hi James, On 12/12/2019 04:02 PM, James Morse wrote: > Hi Bhupesh, I am sorry this review mail skipped my attention due to holidays and focus on other urgent issues. > On 29/11/2019 19:59, Bhupesh Sharma wrote: >> Add documentation for TCR_EL1.T1SZ variable being added to >> vmcoreinfo. >> >> It indicates the size offset of the memory region addressed by TTBR1_EL1 > >> and hence can be used for determining the vabits_actual value. > > used for determining random-internal-kernel-variable, that might not exist tomorrow. > > Could you describe how this is useful/necessary if a debugger wants to walk the page > tables from the core file? I think this is a better argument. > > Wouldn't the documentation be better as part of the patch that adds the export? > (... unless these have to go via different trees? ..) Ok, will fix the same in v6 version. >> diff --git a/Documentation/admin-guide/kdump/vmcoreinfo.rst b/Documentation/admin-guide/kdump/vmcoreinfo.rst >> index 447b64314f56..f9349f9d3345 100644 >> --- a/Documentation/admin-guide/kdump/vmcoreinfo.rst >> +++ b/Documentation/admin-guide/kdump/vmcoreinfo.rst >> @@ -398,6 +398,12 @@ KERNELOFFSET >> The kernel randomization offset. Used to compute the page offset. If >> KASLR is disabled, this value is zero. >> >> +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. > > 'vabits_actual' may not exist when the next person comes to read this documentation (its > going to rot really quickly). > > I think the first half of this text is enough to say what this is for. You should include > words to the effect that its the hardware value that goes with swapper_pg_dir. You may > want to point readers to the arm-arm for more details on what the value means. Ok, got it. Fixed this in v6, which should be on its way shortly. Thanks, Bhupesh