From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mx1.redhat.com ([209.132.183.28]) by bombadil.infradead.org with esmtps (Exim 4.85_2 #1 (Red Hat Linux)) id 1cGNFr-0007JF-VN for kexec@lists.infradead.org; Mon, 12 Dec 2016 09:50:45 +0000 Date: Mon, 12 Dec 2016 17:50:20 +0800 From: "bhe@redhat.com" Subject: Re: [Makedumpfile PATCH V2 2/4] x86_64: translate all VA to PA using page table values Message-ID: <20161212095020.GI1034@x1> References: <0910DD04CBD6DE4193FCF86B9C00BE9701E87E88@BPXM01GP.gisp.nec.co.jp> <3d3fcf63-eb95-9adb-b645-9f906d5f900f@redhat.com> <20161209142515.GB6875@x1> <20161210012915.GA1034@x1> <20161210013330.GC1034@x1> <0910DD04CBD6DE4193FCF86B9C00BE9701E8867A@BPXM01GP.gisp.nec.co.jp> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <0910DD04CBD6DE4193FCF86B9C00BE9701E8867A@BPXM01GP.gisp.nec.co.jp> 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: Atsushi Kumagai Cc: Pratyush Anand , "dyoung@redhat.com" , "louis.bouchard@canonical.com" , "kexec@lists.infradead.org" On 12/12/16 at 08:40am, Atsushi Kumagai wrote: > >On Saturday 10 December 2016 07:03 AM, bhe@redhat.com wrote: > >> On 12/10/16 at 09:29am, Baoquan He wrote: > >>> On 12/09/16 at 10:25pm, Baoquan He wrote: > >>>> On 12/09/16 at 03:40pm, Pratyush Anand wrote: > >>>>>>> - page_dir = SYMBOL(init_level4_pgt); > >>>>>>> + page_dir = SYMBOL(init_level4_pgt) - __START_KERNEL_map + phys_base; > >>>>>> > >>>>>> I found that this change breaks the backward compatibility for > >>>>>> kernel 2.6.21 or older since phys_base was introduced in kernel 2.6.22 > >>>>>> by the commit below: > >>>>>> > >>>>>> commit 1ab60e0f72f71ec54831e525a3e1154f1c092408 > >>>>>> Author: Vivek Goyal > >>>>>> Date: Wed May 2 19:27:07 2007 +0200 > >>>>>> > >>>>>> [PATCH] x86-64: Relocatable Kernel Support > >>>>>> > >>>>>> There is no problem if phys_base is always 0 in older kernel, but > >>>>>> get_phys_base_x86_64() calculates "phys_base = 0x100000" from my vmcore: > >>>> > >>>> This is really awkward. Checked code, found PAGE_OFFSET is > >>>> 0xffff810000000000 before 2.6.26, then changed to 0xffff880000000000 > >>>> after that. Can we check the page_offset calculated from pt_load > >>>> segments, meanwhile check if has VMCOREINFO and osrelease after 2.6.21. > >>>> > >>>> With both of above condition, we could set phys_vase to 0. Not sure if > >>>> this can solve the existing problem. > >>> > >>> I meant making a judgement: > >>> > >> > >> Sorry, should be: > >> if (page_offset == 0xffff810000000000 && !info->kernel_version > KERNEL_VERSION(2, 6, 21)) > >> info->phys_base = 0; > >> > > > > > >But you can not read kernel_version because those version does not have > >VMCOREINFO. So, has_vmcoreinfo() still need to be used. > > Thanks for your comments, using has_vmcoreinfo() sounds like a good approach, > but not perfect way. VMCOREINFO has been introduced since 2.6.24, > 2.6.22 and 2.6.23 don't have VMCOREINFO but have phys_base. > > Conversely, 2.6.22 and 2.6.23 require vmlinux, so we can confirm the existence of > phys_base with that. My idea is: > > diff --git a/arch/x86_64.c b/arch/x86_64.c > index 010ea10..893cd51 100644 > --- a/arch/x86_64.c > +++ b/arch/x86_64.c > @@ -67,6 +67,14 @@ get_phys_base_x86_64(void) > return TRUE; > } > > + /* linux-2.6.21 or older don't have phys_base, should be set to 0. */ > + if (!has_vmcoreinfo()) { > + SYMBOL_INIT(phys_base, "phys_base"); > + if (SYMBOL(phys_base) == NOT_FOUND_SYMBOL) { > + return TRUE; > + } > + } > + > for (i = 0; get_pt_load(i, &phys_start, NULL, &virt_start, NULL); i++) { > if (virt_start >= __START_KERNEL_map) { > > > This fix may resolve my issue, but now I have another question that > "Is the logic of get_phys_base_x86_64() correct in any kernel configuration ?" > I mean I'm worried about the possibility that another offset gets mixed with > the result of get_phys_base_x86_64() like my 2.6.21 case. > After phys_base was introduced, does it always equal to the offset which can be > calculated from PT_LOAD headers ? Don't worry. phys_base was introduced just after 2.6.21. commit 1ab60e0f72f71ec54831e525a3e1154f1c092408 Author: Vivek Goyal Date: Wed May 2 19:27:07 2007 +0200 [PATCH] x86-64: Relocatable Kernel Support [bhe@x1 linux]$ git describe 1ab60e0f72f71ec54831e525a3e1154f1c092408 v2.6.21-1836-g1ab60e0 Thanks Baoquan _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec