Hi James, Bhupesh, If /proc/kcore always exists in kexec/kdump, I think this issue can be fixed easily. But it requires that Kexec/kdump have to rely on " CONFIG_PROC_KCORE=y". I am not sure if we can persuade Kexec-tools community to accept this.
Thanks, Yanjiang > -----Original Message----- > From: Bhupesh Sharma [mailto:bhsha...@redhat.com] > Sent: 2018年6月19日 19:58 > To: James Morse <james.mo...@arm.com> > Cc: Jin, Yanjiang <yanjiang....@hxt-semitech.com>; Will Deacon > <will.dea...@arm.com>; Mark Rutland <mark.rutl...@arm.com>; Ard > Biesheuvel <ard.biesheu...@linaro.org>; Catalin Marinas > <catalin.mari...@arm.com>; Kexec Mailing List <kexec@lists.infradead.org>; > AKASHI Takahiro <takahiro.aka...@linaro.org>; Bhupesh SHARMA > <bhupesh.li...@gmail.com>; linux-arm-kernel <linux-arm- > ker...@lists.infradead.org> > Subject: Re: [PATCH] arm64/mm: Introduce a variable to hold base address of > linear region > > Hi James, > > On Tue, Jun 19, 2018 at 4:56 PM, James Morse <james.mo...@arm.com> wrote: > > Hi Bhupesh, > > > > On 19/06/18 11:37, Bhupesh Sharma wrote: > >> On Tue, Jun 19, 2018 at 3:46 PM, James Morse <james.mo...@arm.com> > wrote: > >>> On 19/06/18 10:57, Jin, Yanjiang wrote: > >>>>> -----Original Message----- > >>>>> From: Will Deacon [mailto:will.dea...@arm.com] > >>>>> Sent: 2018年6月19日 17:41 > >>>>> To: Jin, Yanjiang <yanjiang....@hxt-semitech.com> > >>>>> Cc: James Morse <james.mo...@arm.com>; Bhupesh Sharma > >>>>> <bhsha...@redhat.com>; Mark Rutland <mark.rutl...@arm.com>; Ard > >>>>> Biesheuvel <ard.biesheu...@linaro.org>; Catalin Marinas > >>>>> <catalin.mari...@arm.com>; Kexec Mailing List > >>>>> <kexec@lists.infradead.org>; AKASHI Takahiro > >>>>> <takahiro.aka...@linaro.org>; Bhupesh SHARMA > >>>>> <bhupesh.li...@gmail.com>; linux-arm-kernel <linux-arm- > >>>>> ker...@lists.infradead.org> > >>>>> Subject: Re: [PATCH] arm64/mm: Introduce a variable to hold base > >>>>> address of linear region > > > >>>>>>>> It is hard to know all above in kexec-tools now. Originally I > >>>>>>>> planned to read memstart_addr's value from "/dev/mem", but > >>>>>>>> someone thought not all Kernels enable "/dev/mem", we'd better > >>>>>>>> find a more generic approach. So we want to get some > >>>>>>>> suggestions from ARM kernel > >>>>> community. > >>>>>>>> Can we export this variable in Kernel side through sysconf() or > >>>>>>>> other similar methods? Or someone can provide an effect way to > >>>>>>>> get memstart_addr's value? > >>>>>>> > >>>>>>> I thought the suggestion from James was to expose this via an > >>>>>>> ELF NOTE in kcore and vmcore (or in the header directly if > >>>>>>> that's possible, but I'm > >>>>> not sure about it)? > >>>>>> > >>>>>> Thanks for your reply firstly. But same as DEVMEM, kcore is not a > >>>>>> must-have, so we can't depend on it. > >>>>> > >>>>> Neither is KEXEC. We can select PROC_KCORE from KEXEC if it helps. > >>>>> > >>>>>> On the other hand, phys_to_virt() is called during generating > >>>>>> vmcore in Kexec-tools, vmcore also can't help this issue. > >>>>> > >>>>> I don't understand this part. If you have the vmcore in your hand, > >>>>> why can't you grok the pv offset from the note and use that in > phys_to_virt()? > >>>> > >>>> It is a chicken-and-egg issue. > >>>> phys_to virt() is for crashdump setup. To generate vmcore, we must > >>>> call phys_to_virt(). At this point, no vmcore exists. > >>> > >>> Its needed for the parts of the ELF header that kexec-tools > >>> generates at kdump load time? > >>> > >>> So adding this pv_offset to the key=value data > >>> crash_save_vmcoreinfo_init() saves isn't available early enough? > > > >> Yes, one case where it is not actually available early enough for > >> makedumpfile usage is if we are determining the PT_NOTE contents from > >> the '/proc/kcore' on a 'live' system > > > >> int set_kcore_vmcoreinfo(uint64_t vmcoreinfo_addr, uint64_t > >> vmcoreinfo_len) > >> > >> { > >> > >> <snip..> > >> kvaddr = (ulong)vmcoreinfo_addr + PAGE_OFFSET; > >> > >> } > > > > You are trying to read the vmcoreinfo through /proc/kcore given > > knowledge of its physical address. > > > > I'm suggesting adding the contents of vmcoreinfo as a PT_NOTE section > > of /proc/kcore's ELF header. No special knowledge necessary, any > > elf-parser should be able to dump the values. > > > > > >> Now the problem at hand is to determine the offset at which the > >> pv_offset (key=value data pair) lies in the '/proc/kcore' (I assume > >> that when you mentioned above and earlier about adding this pair to > >> the elfnotes you meant both the vmcoreinfo and 'proc/kcore'), as we > >> can have 'n' number of PT_LOAD segments. > > > > It looks like there is already a NOTE section with core info in there: > > | # readelf -l /proc/kcore > > | > > | Elf file type is CORE (Core file) > > | Entry point 0x0 > > | There are 16 program headers, starting at offset 64 > > | > > | Program Headers: > > | Type Offset VirtAddr PhysAddr > > | FileSiz MemSiz Flags Align > > | NOTE 0x00000000000003c0 0x0000000000000000 0x0000000000000000 > > | 0x0000000000001114 0x0000000000000000 0x0 > > > > I assume we can add more notes without breaking the existing user... > > > > (and it looks like there are some broken __pa(kernel symbol) users in there. > > Thanks for your inputs. > > I am working on fixes on the above lines for kernel and user-space tools (like > makedumpfile, crash-utility and kexec-tools). > > I will post some RFC patches on the same lines (or come back in case I get > stuck > somewhere) shortly. > > Thanks, > Bhupesh This email is intended only for the named addressee. 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