From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965666AbcA1OBm (ORCPT ); Thu, 28 Jan 2016 09:01:42 -0500 Received: from e06smtp15.uk.ibm.com ([195.75.94.111]:36686 "EHLO e06smtp15.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933174AbcA1OBi (ORCPT ); Thu, 28 Jan 2016 09:01:38 -0500 X-IBM-Helo: d06dlp01.portsmouth.uk.ibm.com X-IBM-MailFrom: holzheu@linux.vnet.ibm.com X-IBM-RcptTo: linux-kernel@vger.kernel.org;linux-s390@vger.kernel.org Date: Thu, 28 Jan 2016 15:01:28 +0100 From: Michael Holzheu To: xlpang@redhat.com Cc: xpang@redhat.com, Andrew Morton , linux-s390@vger.kernel.org, Dmitry Safonov , heiko.carstens@de.ibm.com, linux-kernel@vger.kernel.org, ebiederm@xmission.com, 0x7f454c46@gmail.com, schwidefsky@de.ibm.com, dyoung@redhat.com, kexec@lists.infradead.org Subject: Re: [PATCH] kexec: unmap reserved pages for each error-return way Message-ID: <20160128150128.564bfcdd@holzheu> In-Reply-To: <56AA13D6.20808@redhat.com> References: <1453895311-11087-1-git-send-email-dsafonov@virtuozzo.com> <20160127111546.2212f191f5f313b613f6b60b@linux-foundation.org> <20160128113217.79d37ff5@holzheu> <56AA0208.7050508@redhat.com> <20160128134432.7f25bf77@holzheu> <56AA13D6.20808@redhat.com> Organization: IBM X-Mailer: Claws Mail 3.8.0 (GTK+ 2.24.10; i686-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16012814-0021-0000-0000-00001FF90DCC Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 28 Jan 2016 21:12:54 +0800 Xunlei Pang wrote: > On 2016/01/28 at 20:44, Michael Holzheu wrote: > > On Thu, 28 Jan 2016 19:56:56 +0800 > > Xunlei Pang wrote: > > > >> On 2016/01/28 at 18:32, Michael Holzheu wrote: > >>> On Wed, 27 Jan 2016 11:15:46 -0800 > >>> Andrew Morton wrote: > >>> > >>>> On Wed, 27 Jan 2016 14:48:31 +0300 Dmitry Safonov wrote: > >>>> > >>>>> For allocation of kimage failure or kexec_prepare or load segments > >>>>> errors there is no need to keep crashkernel memory mapped. > >>>>> It will affect only s390 as map/unmap hook defined only for it. > >>>>> As on unmap s390 also changes os_info structure let's check return code > >>>>> and add info only on success. > >>>>> > >>>> This conflicts (both mechanically and somewhat conceptually) with > >>>> Xunlei Pang's "kexec: Introduce a protection mechanism for the > >>>> crashkernel reserved memory" and "kexec: provide > >>>> arch_kexec_protect(unprotect)_crashkres()". > >>>> > >>>> http://ozlabs.org/~akpm/mmots/broken-out/kexec-introduce-a-protection-mechanism-for-the-crashkernel-reserved-memory.patch > >>>> http://ozlabs.org/~akpm/mmots/broken-out/kexec-introduce-a-protection-mechanism-for-the-crashkernel-reserved-memory-v4.patch > >>>> > >>>> and > >>>> > >>>> http://ozlabs.org/~akpm/mmots/broken-out/kexec-provide-arch_kexec_protectunprotect_crashkres.patch > >>>> http://ozlabs.org/~akpm/mmots/broken-out/kexec-provide-arch_kexec_protectunprotect_crashkres-v4.patch > >>> Hmm, It looks to me that arch_kexec_(un)protect_crashkres() has exactly > >>> the same semantics as crash_(un)map_reserved_pages(). > >>> > >>> On s390 we don't have the crashkernel memory mapped and therefore need > >>> crash_map_reserved_pages() before loading something into crashkernel > >>> memory. > >> I don't know s390, just curious, if s390 doesn't have crash kernel memory mapped, > >> what's the purpose of the commit(558df7209e) for s390 as the reserved crash memory > >> with no kernel mapping already means the protection is on? > > When we reserve crashkernel memory on s390 ("crashkernel=" kernel parameter), > > we create a memory hole without page tables. > > > > Commit (558df7209e) was necessary to load a kernel/ramdisk into > > the memory hole with the kexec() system call. > > > > We create a temporary mapping with crash_map_reserved_pages(), then > > copy the kernel/ramdisk and finally remove the mapping again > > via crash_unmap_reserved_pages(). > > Thanks for the explanation. > So, on s390 the physical memory address has the same value as its kernel virtual address, > and kmap() actually returns the value of the physical address of the page, right? Correct. On s390 kmap() always return the physical address of the page. We have an 1:1 mapping for all the physical memory. For this area virtual=real. In addition to that we have the vmalloc area above the 1:1 mapping where some of the memory is mapped a second time. Michael