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 1c1qVD-0006bV-Hn for kexec@lists.infradead.org; Wed, 02 Nov 2016 08:02:32 +0000 Date: Wed, 2 Nov 2016 16:02:05 +0800 From: "bhe@redhat.com" Subject: Re: [PATCH Makedumpfile 1/4] x86_64: Calculate page_offset from pt_load Message-ID: <20161102080205.GA6084@x1> References: <4b2497eff40bd47eef59cdd6af165e700cfd4408.1477327674.git.panand@redhat.com> <0910DD04CBD6DE4193FCF86B9C00BE9701E7C84F@BPXM01GP.gisp.nec.co.jp> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <0910DD04CBD6DE4193FCF86B9C00BE9701E7C84F@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 , "kexec@lists.infradead.org" , "dyoung@redhat.com" On 11/02/16 at 07:40am, Atsushi Kumagai wrote: > Hello Pratyush, > > >On Monday 24 October 2016 10:18 PM, Pratyush Anand wrote: > >> page_offset can always be calculated as 'virtual - physical' for a direct > >> mapping area on x86. Therefore, remove the version dependent calculation > >> and use this method. > >> > >> Signed-off-by: Pratyush Anand > >> --- > >> arch/x86_64.c | 24 ++++++++++++++++++++---- > >> 1 file changed, 20 insertions(+), 4 deletions(-) > >> > >> diff --git a/arch/x86_64.c b/arch/x86_64.c > >> index ddf7be6bc57b..a96fd8ae00a1 100644 > >> --- a/arch/x86_64.c > >> +++ b/arch/x86_64.c > >> @@ -44,6 +44,24 @@ get_xen_p2m_mfn(void) > >> return NOT_FOUND_LONG_VALUE; > >> } > >> > >> +static int > >> +get_page_offset_x86_64(void) > >> +{ > >> + int i; > >> + unsigned long long phys_start; > >> + unsigned long long virt_start; > >> + > >> + for (i = 0; get_pt_load(i, &phys_start, NULL, &virt_start, NULL); i++) { > >> + if (virt_start >= __START_KERNEL_map) { > > > >OK..So, this is the problem. We should have > > > >if (virt_start < __START_KERNEL_map) { > > > >Kernel text region lies above __START_KERNEL_map, which is linearly > >mapped however not a direct mapping. Direct mapping region lies below it > >instead. So, page_offset can only be calculated with a region which is > >below __START_KERNEL_map. > > > >Thanks Baoquan for finding it. > > Could you explain the issue in more detail, what is the difference > between "linear map" and "direct map" ? Well, these could be easily misunderstood. Virtual address in kernel text region or within direct mapping which is from PAGE_OFFSET are all linear mapping. Because the related PA can be calculated by: PA= VA - PAGE_OFFSET; //y=x - a; PA= VA - __START_KERNEL_map + phys_base; //y=x-a+b In user-space kexec-tools we created pt_load program segments for kernel text region and crash memory regions. The first program header is kernel text region. So here if we want to get page_offset, just need to ignore the 1st one, kernel text region. > > BTW, I confirmed that the difference of v2 patch is only this and > the result of benchmark looks great, thank you very much. > > > Regards, > Atsushi Kumagai > > >> + info->page_offset = virt_start - phys_start; > >> + return TRUE; > >> + } > >> + } > >> + > >> + ERRMSG("Can't get any pt_load to calculate page offset.\n"); > >> + return FALSE; > >> +} > >> + > >> int > >> get_phys_base_x86_64(void) > >> { > >> @@ -159,10 +177,8 @@ get_versiondep_info_x86_64(void) > >> else > >> info->max_physmem_bits = _MAX_PHYSMEM_BITS_2_6_31; > >> > >> - if (info->kernel_version < KERNEL_VERSION(2, 6, 27)) > >> - info->page_offset = __PAGE_OFFSET_ORIG; > >> - else > >> - info->page_offset = __PAGE_OFFSET_2_6_27; > >> + if (!get_page_offset_x86_64()) > >> + return FALSE; > >> > >> if (info->kernel_version < KERNEL_VERSION(2, 6, 31)) { > >> info->vmalloc_start = VMALLOC_START_ORIG; > >> > > > >_______________________________________________ > >kexec mailing list > >kexec@lists.infradead.org > >http://lists.infradead.org/mailman/listinfo/kexec _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec