From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from out01.mta.xmission.com ([166.70.13.231]) by merlin.infradead.org with esmtps (Exim 4.80.1 #2 (Red Hat Linux)) id 1UI3zN-0000W1-KL for kexec@lists.infradead.org; Tue, 19 Mar 2013 21:22:34 +0000 From: ebiederm@xmission.com (Eric W. Biederman) References: <20130316040003.15064.62308.stgit@localhost6.localdomain6> <20130316040228.15064.28019.stgit@localhost6.localdomain6> <20130319130229.fe83c985678146980ecc6102@linux-foundation.org> Date: Tue, 19 Mar 2013 14:22:22 -0700 In-Reply-To: <20130319130229.fe83c985678146980ecc6102@linux-foundation.org> (Andrew Morton's message of "Tue, 19 Mar 2013 13:02:29 -0700") Message-ID: <87fvzrozjl.fsf@xmission.com> MIME-Version: 1.0 Subject: Re: [PATCH v3 18/21] vmcore: check if vmcore objects satify mmap()'s page-size boundary requirement 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: Andrew Morton Cc: kexec@lists.infradead.org, heiko.carstens@de.ibm.com, linux-kernel@vger.kernel.org, lisa.mitchell@hp.com, HATAYAMA Daisuke , kumagai-atsushi@mxc.nes.nec.co.jp, zhangyanfei@cn.fujitsu.com, cpw@sgi.com, vgoyal@redhat.com Andrew Morton writes: > On Sat, 16 Mar 2013 13:02:29 +0900 HATAYAMA Daisuke wrote: > >> If there's some vmcore object that doesn't satisfy page-size boundary >> requirement, remap_pfn_range() fails to remap it to user-space. >> >> Objects that posisbly don't satisfy the requirement are ELF note >> segments only. The memory chunks corresponding to PT_LOAD entries are >> guaranteed to satisfy page-size boundary requirement by the copy from >> old memory to buffer in 2nd kernel done in later patch. >> >> This patch doesn't copy each note segment into the 2nd kernel since >> they amount to so large in total if there are multiple CPUs. For >> example, current maximum number of CPUs in x86_64 is 5120, where note >> segments exceed 1MB with NT_PRSTATUS only. > > I don't really understand this. Why does the number of or size of > note segments affect their alignment? > >> --- a/fs/proc/vmcore.c >> +++ b/fs/proc/vmcore.c >> @@ -38,6 +38,8 @@ static u64 vmcore_size; >> >> static struct proc_dir_entry *proc_vmcore = NULL; >> >> +static bool support_mmap_vmcore; > > This is quite regrettable. It means that on some kernels/machines, > mmap(vmcore) simply won't work. This means that people might write > code which works for them, but which will fail for others when deployed > on a small number of machines. > > Can we avoid this? Why can't we just copy the notes even if there are > a large number of them? Yes. If it simplifies things I don't see a need to support mmapping everything. But even there I don't see much of an issue. Today we allocate a buffer to hold the ELF header program headers and the note segment, and we could easily allocate that buffer in such a way to make it mmapable. Eric _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec