From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mail-pf0-x22b.google.com ([2607:f8b0:400e:c00::22b]) by bombadil.infradead.org with esmtps (Exim 4.85_2 #1 (Red Hat Linux)) id 1bG092-0002gU-Do for kexec@lists.infradead.org; Thu, 23 Jun 2016 08:37:53 +0000 Received: by mail-pf0-x22b.google.com with SMTP id h14so26706863pfe.1 for ; Thu, 23 Jun 2016 01:37:31 -0700 (PDT) Date: Thu, 23 Jun 2016 17:42:28 +0900 From: AKASHI Takahiro Subject: Re: [PATCH v19 10/13] arm64: kdump: add VMCOREINFO's for user-space coredump tools Message-ID: <20160623081545.GA20774@linaro.org> References: <6e96110e85e7b1167043d789e85f9c916fdf281a.1466120418.git.geoff@infradead.org> <20160620053222.GB14309@dhcppc9> <20160622055940.GY20774@linaro.org> <20160623071412.GA16398@dhcppc9> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20160623071412.GA16398@dhcppc9> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "kexec" Errors-To: kexec-bounces+dwmw2=infradead.org@lists.infradead.org To: Pratyush Anand Cc: Mark Rutland , Geoff Levand , Catalin Marinas , Atsushi Kumagai , Will Deacon , marc.zyngier@arm.com, James Morse , kexec@lists.infradead.org, linux-arm-kernel@lists.infradead.org On Thu, Jun 23, 2016 at 12:44:12PM +0530, Pratyush Anand wrote: > Hi Takahiro, > > Thanks for your reply. > > On 22/06/2016:02:59:41 PM, AKASHI Takahiro wrote: > > On Mon, Jun 20, 2016 at 11:02:22AM +0530, Pratyush Anand wrote: > > > +Atsushi > > > > > > Hi Takahiro, > > > > > > On 16/06/2016:11:48:28 PM, Geoff Levand wrote: > > > > From: AKASHI Takahiro > > > > > > > > For the current crash utility, we need to know, at least, > > > > - kimage_voffset > > > > - PHYS_OFFSET > > > > to handle the contents of core dump file (/proc/vmcore) correctly due to > > > > the introduction of KASLR (CONFIG_RANDOMIZE_BASE) in v4.6. > > > > This patch puts them as VMCOREINFO's into the file. > > > > > > > > - VA_BITS > > > > is also added for makedumpfile command. > > > > > > Thanks for adding them. They are quite helpful for makedumpfile as well. > > > > > > > More VMCOREINFO's may be added later. > > > > > > Yes, we will need to pass VMCOREINFO_SYMBOL(_text) and VMCOREINFO_SYMBOL(_end) > > > in order to work with makedumpfile. > > > > I know that adding those symbols is the easiest way, but > > theoretically, if we know the physical address of "swapper_pg_dir", > > But, we know only it's virtual address. What I meant here is that, if we know the physical address of "swapper_pg_dir", we don't have to know neither of "_text", "_end", "kimage_voffset" nor "PHYS_OFFSET". I just wanted to ask you whether you thought of this possibility. > > > instead of its virtual address, we can access all the memory pointed to > > by any kernel virtual address. > > How do you rationalize that we need to know "_text" and "_end"? > > Well, we need some mechanism so that we can decide if an address can be > translated using linear mapping of virt_to_phys(). All the entries in MMU tables are based on "physical" addresses, and so we don't care whether a given address is in linear mapping or not in walking through MMU. See what I mean? Thanks, -Takahiro AKASHI > Alternatively, probably we can do like this: > -- Translate all address between "SYMBOL(swapper_pg_dir)" and "SYMBOL(swapper_pg_dir) > + SWAPPER_DIR_SIZE" using virt_to_phys() and now we can read values from > dumpfile using that physical address. This way we can get PGD/PMD/PUD values. > -- PTE values may lie out side this range, however that address should still be > linearly translatable. We can use virt_to_phys() macro from them as well. > > In summary, we can translate address of PGD/PMD/PUD/PTE using virt_to_phys() > and rest all can be translated using page table entries. > > ~Pratyush _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec