From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from tyo201.gate.nec.co.jp ([210.143.35.51]) by bombadil.infradead.org with esmtps (Exim 4.85_2 #1 (Red Hat Linux)) id 1c2bv6-0003Ti-UM for kexec@lists.infradead.org; Fri, 04 Nov 2016 10:40:26 +0000 From: Atsushi Kumagai Subject: RE: [PATCH Makedumpfile 1/4] x86_64: Calculate page_offset from pt_load Date: Fri, 4 Nov 2016 10:35:49 +0000 Message-ID: <0910DD04CBD6DE4193FCF86B9C00BE9701E7CFF3@BPXM01GP.gisp.nec.co.jp> References: <4b2497eff40bd47eef59cdd6af165e700cfd4408.1477327674.git.panand@redhat.com> <0910DD04CBD6DE4193FCF86B9C00BE9701E7C84F@BPXM01GP.gisp.nec.co.jp> <20161102080205.GA6084@x1> In-Reply-To: <20161102080205.GA6084@x1> Content-Language: ja-JP MIME-Version: 1.0 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: "bhe@redhat.com" Cc: Pratyush Anand , "dyoung@redhat.com" , "kexec@lists.infradead.org" Hello, >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. Thanks, I understand. Now I have no concerns. Regards, Atsushi Kumagai >> 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 _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec