在 2019年01月07日 15:55, Hatayama, Daisuke 写道: > Hi, > >> -----Original Message----- >> From: linux-kernel-owner@xxxxxxxxxxxxxxx >> [mailto:linux-kernel-owner@xxxxxxxxxxxxxxx] On Behalf Of Lianbo Jiang >> Sent: Monday, January 7, 2019 10:48 AM >> To: linux-kernel@xxxxxxxxxxxxxxx >> Cc: kexec@xxxxxxxxxxxxxxxxxxx; tglx@xxxxxxxxxxxxx; mingo@xxxxxxxxxx; >> bp@xxxxxxxxx; x86@xxxxxxxxxx; akpm@xxxxxxxxxxxxxxxxxxxx; bhe@xxxxxxxxxx; >> dyoung@xxxxxxxxxx; linux-doc@xxxxxxxxxxxxxxx; k-hagio@xxxxxxxxxxxxx; >> anderson@xxxxxxxxxx >> Subject: [PATCH 1/2 v5] kdump: add the vmcoreinfo documentation >> >> This document lists some variables that export to vmcoreinfo, and briefly >> describles what these variables indicate. It should be instructive for >> many people who do not know the vmcoreinfo, and it also normalizes the > > I agree to this part, but > >> exported variables as a convention between kernel and use-space. > > I don't agree to this part. > > The meaning of each symbol is decided by each feature in the kernel, > not by vmcoreinfo. I suspect anyone mistakenly understand this document is > ABI enforcing each symbol works as described. We can change symbols and > their meaning regardless of this document. > > Oh, I found this topic has already been discussed at v3, and > you removed "ABI" in the patch description at v4. > > But it seems still confusing to me. > I think the explicit description saying that this is for user-land tools, > they treats each symbol as described, > and the document never affect implementation of each kernel components, > is necessary in e.g. "Purpose of this document" section? > Thanks for your advice. If this part could make the document become a rope tied around our necks, i would like to remove this part from the patch log in next post. Regards, Lianbo >> >> Suggested-by: Borislav Petkov <bp@xxxxxxx> >> Signed-off-by: Lianbo Jiang <lijiang@xxxxxxxxxx> >> --- >> Documentation/kdump/vmcoreinfo.txt | 500 +++++++++++++++++++++++++++++ >> 1 file changed, 500 insertions(+) >> create mode 100644 Documentation/kdump/vmcoreinfo.txt >> >> diff --git a/Documentation/kdump/vmcoreinfo.txt >> b/Documentation/kdump/vmcoreinfo.txt >> new file mode 100644 >> index 000000000000..8e444586b87b >> --- /dev/null >> +++ b/Documentation/kdump/vmcoreinfo.txt >> @@ -0,0 +1,500 @@ >> +================================================================ >> + VMCOREINFO >> +================================================================ >> + >> +======================= >> +What is the VMCOREINFO? >> +======================= >> + >> +VMCOREINFO is a special ELF note section. It contains various >> +information from the kernel like structure size, page size, symbol >> +values, field offsets, etc. These data are packed into an ELF note >> +section and used by user-space tools like crash and makedumpfile to >> +analyze a kernel's memory layout. >> + >> +================ >> +Common variables >> +================ >> + >> +init_uts_ns.name.release >> +------------------------ >> + >> +The version of the Linux kernel. Used to find the corresponding source >> +code from which the kernel has been built. >> + >> +PAGE_SIZE >> +--------- >> + >> +The size of a page. It is the smallest unit of data for memory >> +management in kernel. It is usually 4096 bytes and a page is aligned >> +on 4096 bytes. Used for computing page addresses. >> + >> +init_uts_ns >> +----------- >> + >> +This is the UTS namespace, which is used to isolate two specific >> +elements of the system that relate to the uname(2) system call. The UTS >> +namespace is named after the data structure used to store information >> +returned by the uname(2) system call. >> + >> +User-space tools can get the kernel name, host name, kernel release >> +number, kernel version, architecture name and OS type from it. >> + >> +node_online_map >> +--------------- >> + >> +An array node_states[N_ONLINE] which represents the set of online node >> +in a system, one bit position per node number. Used to keep track of >> +which nodes are in the system and online. >> + >> +swapper_pg_dir >> +------------- >> + >> +The global page directory pointer of the kernel. Used to translate >> +virtual to physical addresses. >> + >> +_stext >> +------ >> + >> +Defines the beginning of the text section. In general, _stext indicates >> +the kernel start address. Used to convert a virtual address from the >> +direct kernel map to a physical address. >> + >> +vmap_area_list >> +-------------- >> + >> +Stores the virtual area list. makedumpfile can get the vmalloc start >> +value from this variable. This value is necessary for vmalloc translation. >> + >> +mem_map >> +------- >> + >> +Physical addresses are translated to struct pages by treating them as >> +an index into the mem_map array. Right-shifting a physical address >> +PAGE_SHIFT bits converts it into a page frame number which is an index >> +into that mem_map array. >> + >> +Used to map an address to the corresponding struct page. >> + >> +contig_page_data >> +---------------- >> + >> +Makedumpfile can get the pglist_data structure from this symbol, which >> +is used to describe the memory layout. >> + >> +User-space tools use this to exclude free pages when dumping memory. >> + >> +mem_section|(mem_section, NR_SECTION_ROOTS)|(mem_section, section_mem_map) >> +------------------------------------------------------------------------- >> - >> + >> +The address of the mem_section array, its length, structure size, and >> +the section_mem_map offset. >> + >> +It exists in the sparse memory mapping model, and it is also somewhat >> +similar to the mem_map variable, both of them are used to translate an >> +address. >> + >> +page >> +---- >> + >> +The size of a page structure. struct page is an important data structure >> +and it is widely used to compute the contiguous memory. >> + >> +pglist_data >> +----------- >> + >> +The size of a pglist_data structure. This value will be used to check >> +if the pglist_data structure is valid. It is also used for checking the >> +memory type. >> + >> +zone >> +---- >> + >> +The size of a zone structure. This value is often used to check if the >> +zone structure has been found. It is also used for excluding free pages. >> + >> +free_area >> +--------- >> + >> +The size of a free_area structure. It indicates whether the free_area >> +structure is valid or not. Useful for excluding free pages. >> + >> +list_head >> +--------- >> + >> +The size of a list_head structure. Used when iterating lists in a >> +post-mortem analysis session. >> + >> +nodemask_t >> +---------- >> + >> +The size of a nodemask_t type. Used to compute the number of online >> +nodes. >> + >> +(page, flags|_refcount|mapping|lru|_mapcount|private|compound_dtor| >> + compound_order|compound_head) >> +------------------------------------------------------------------- >> + >> +User-space tools can compute their values based on the offset of these >> +variables. The variables are helpful to exclude unnecessary pages. >> + >> +(pglist_data, node_zones|nr_zones|node_mem_map|node_start_pfn|node_ >> + spanned_pages|node_id) >> +------------------------------------------------------------------- >> + >> +On NUMA machines, each NUMA node has a pg_data_t to describe its memory >> +layout. On UMA machines there is a single pglist_data which describes the >> +whole memory. >> + >> +These values are used to check the memory type, and they are also helpful >> +to compute the virtual address for memory map. >> + >> +(zone, free_area|vm_stat|spanned_pages) >> +--------------------------------------- >> + >> +Each node is divided into a number of blocks called zones which >> +represent ranges within memory. A zone is described by a structure zone. >> +Each zone type is suitable for a different type of usage. >> + >> +User-space tools can compute required values based on the offset of these >> +variables. >> + >> +(free_area, free_list) >> +---------------------- >> + >> +Offset of the free_list's member. This value is used to compute the number >> +of free pages. >> + >> +Each zone has a free_area structure array called free_area[MAX_ORDER]. >> +The fields in this structure are simple, the free_list represents a linked >> +list of free page blocks. >> + >> +(list_head, next|prev) >> +---------------------- >> + >> +Offsets of the list_head's members. list_head is used to define a >> +circular linked list. User-space tools need these in order to traverse >> +lists. >> + >> +(vmap_area, va_start|list) >> +-------------------------- >> + >> +Offsets of the vmap_area's members. They indicate the vmalloc layer >> +information. Makedumpfile gets the start address of the vmalloc region. >> + >> +(zone.free_area, MAX_ORDER) >> +--------------------------- >> + >> +It indicates the maximum number of the array free_area. This macro is >> +used by the zone buddy allocator. User-space tools use this value to >> +iterate the free_area. >> + >> +log_buf >> +------- >> + >> +Console output is written to the ring buffer log_buf at index >> +log_first_idx. Used to get the kernel log. >> + >> +log_buf_len >> +----------- >> + >> +Length of a log_buf. Used to read the number of strings from the >> +log_buf. >> + >> +log_first_idx >> +------------- >> + >> +Index of the first record stored in the buffer log_buf. Used by >> +user-space tools to read the strings in the log_buf. >> + >> +clear_idx >> +--------- >> + >> +The index that the next printk() record to read after the last clear >> +command. It indicates the first record after the last SYSLOG_ACTION >> +_CLEAR, like issued by 'dmesg -c'. Used by user-space tools to dump >> +the dmesg log. >> + >> +log_next_idx >> +------------ >> + >> +The index of the next record to store in the buffer log_buf. Used to >> +compute the index of the current string position. >> + >> +printk_log >> +---------- >> + >> +The size of a structure printk_log. Used to compute the size of >> +messages, and extract dmesg log. It can output human readable text. >> +Encapsulate header information for log_buf, such as timestamp, syslog >> +level, etc. >> + >> +(printk_log, ts_nsec|len|text_len|dict_len) >> +------------------------------------------- >> + >> +It represents field offsets in struct printk_log. User space tools can >> +parse it and check whether the values of printk_log's members have been >> +changed. >> + >> +(free_area.free_list, MIGRATE_TYPES) >> +------------------------------------ >> + >> +The number of migrate types for pages. The free_list is divided into >> +the array, it needs to know the number of the array when makedumpfile >> +computes the number of free pages. >> + >> +NR_FREE_PAGES >> +------------- >> + >> +On linux-2.6.21 or later, the number of free_pages is in >> +vm_stat[NR_FREE_PAGES]. Used to get the number of free pages. >> + >> +PG_lru|PG_private|PG_swapcache|PG_swapbacked|PG_slab|PG_hwpoision >> +|PG_head_mask|PAGE_BUDDY_MAPCOUNT_VALUE(~PG_buddy) >> +|PAGE_OFFLINE_MAPCOUNT_VALUE(~PG_offline) >> +----------------------------------------------------------------- >> + >> +Page attributes. These flags are used to filter various unnecessary >> +pages. >> + >> +HUGETLB_PAGE_DTOR >> +----------------- >> + >> +The HUGETLB_PAGE_DTOR flag denotes hugetlbfs pages. Makedumpfile >> +excludes these pages. >> + >> +====== >> +x86_64 >> +====== >> + >> +phys_base >> +--------- >> + >> +Used to convert the virtual address of an exported kernel symbol to its >> +physical address. >> + >> +init_top_pgt >> +------------ >> + >> +Used to walk through the whole page table and convert virtual addresses >> +to physical addresses. The init_top_pgt is somewhat similar to the >> +swapper_pg_dir, but it is only used in x86_64. >> + >> +pgtable_l5_enabled >> +------------------ >> + >> +User-space tools need to know whether the crash kernel was in 5-level >> +paging mode. >> + >> +node_data >> +--------- >> + >> +This is a struct pglist_data array and stores all numa nodes >> +information. Makedumpfile gets the pglist_data structure from it. >> + >> +(node_data, MAX_NUMNODES) >> +------------------------- >> + >> +The maximum number of the nodes in system. >> + >> +KERNELOFFSET >> +------------ >> + >> +The kernel randomization offset. Used to compute the page offset. If >> +KASLR is disabled, this value is zero. >> + >> +KERNEL_IMAGE_SIZE >> +----------------- >> + >> +Currently unused by Makedumpfile. Used to compute the module virtual >> +address by Crash. >> + >> +sme_mask >> +-------- >> + >> +For AMD machine with SME feature, it indicates the secure memory >> +encryption mask. Makedumpfile tools need to know whether the crash >> +kernel was encrypted. If SME is enabled in the first kernel, the crash >> +kernel's page table (pgd/pud/pmd/pte) contains the memory encryption >> +mask and this is used to remove the SME mask to obtain the true physical >> +address. >> + >> +Currently, the sme_mask stores the value of sme_me_mask(bit 47). If need, >> +the bit(sme_mask) might be redefined in the future, but the bit 63 will >> +be reserved. >> + >> +For example: >> +[ misc ][ enc bit ][ other misc SME info ] >> +0000_0000_0000_0000_1000_0000_0000_0000_0000_0000_..._0000 >> +63 59 55 51 47 43 39 35 31 27 ... 3 >> + >> +====== >> +x86_32 >> +====== >> + >> +X86_PAE >> +------- >> + >> +Denotes whether physical address extensions are enabled. It has the cost >> +of more page table lookup overhead, and also consumes more page table >> +space per process. Used to check whether PAE was enabled in the crash >> +kernel when converting virtual addresses to physical addresses. >> + >> +==== >> +ia64 >> +==== >> + >> +pgdat_list|(pgdat_list, MAX_NUMNODES) >> +------------------------------------- >> + >> +pg_data_t array storing all numa nodes information. MAX_NUMNODES >> +indicates the number of the nodes. >> + >> +node_memblk|(node_memblk, NR_NODE_MEMBLKS) >> +------------------------------------------ >> + >> +List of node memory chunks. Filled when parsing SRAT table to obtain >> +information about memory nodes. NR_NODE_MEMBLKS indicates the number >> +of node memory chunks. >> + >> +These values are used to compute the number of nodes in the crash kernel. >> + >> +node_memblk_s|(node_memblk_s, start_paddr)|(node_memblk_s, size) >> +---------------------------------------------------------------- >> + >> +The size of a struct node_memblk_s and the offsets of the >> +node_memblk_s's members. Used to compute the number of nodes. >> + >> +PGTABLE_3|PGTABLE_4 >> +------------------- >> + >> +User-space tools need to know whether the crash kernel was in 3-level or >> +4-level paging mode. Used to distinguish the page table. >> + >> +===== >> +ARM64 >> +===== >> + >> +VA_BITS >> +------- >> + >> +The maximum number of bits for virtual addresses. Used to compute the >> +virtual memory ranges. >> + >> +kimage_voffset >> +-------------- >> + >> +The offset between the kernel virtual and physical mappings. Used to >> +translate virtual to physical addresses. >> + >> +PHYS_OFFSET >> +----------- >> + >> +Indicates the physical address of the start of memory. Similar to >> +kimage_voffset, which is used to translate virtual address to physical >> +address. >> + >> +KERNELOFFSET >> +------------ >> + >> +The kernel randomization offset. Used to compute the page offset. If >> +KASLR is disabled, this value is zero. >> + >> +==== >> +arm >> +==== >> + >> +ARM_LPAE >> +-------- >> + >> +It indicates whether the crash kernel supports large physical address >> +extensions. Used to translate virtual address to physical address. >> + >> +==== >> +s390 >> +==== >> + >> +lowcore_ptr >> +---------- >> + >> +An array with a pointer to the lowcore of every CPU. Used to print the >> +psw and all registers information. >> + >> +high_memory >> +----------- >> + >> +Used to get the vmalloc_start address from the high_memory symbol. >> + >> +(lowcore_ptr, NR_CPUS) >> +---------------------- >> + >> +The maximum number of CPUs. >> + >> +======= >> +powerpc >> +======= >> + >> + >> +node_data|(node_data, MAX_NUMNODES) >> +----------------------------------- >> + >> +See above. >> + >> +contig_page_data >> +---------------- >> + >> +See above. >> + >> +vmemmap_list >> +------------ >> + >> +The vmemmap_list maintains the entire vmemmap physical mapping. It can >> +get vmemmap list count and populate vmemmap regions info. If the vmemmap >> +address translation information is stored in the crash kernel, it helps >> +to translate vmemmap kernel virtual addresses. >> + >> +mmu_vmemmap_psize >> +----------------- >> + >> +The size of a page. Used to translate address to physical addresses. >> + >> +mmu_psize_defs >> +-------------- >> + >> +Page size definitions, i.e. 4k, 64k, or 16M. >> + >> +Used to make vtop translations. >> + >> +vmemmap_backing|(vmemmap_backing, list)|(vmemmap_backing, phys)| >> +(vmemmap_backing, virt_addr) >> +---------------------------------------------------------------- >> + >> +The vmemmap virtual address space management does not have a traditional >> +page table to track which virtual struct pages are backed by physical >> +mapping. The virtual to physical mappings are tracked in a simple linked >> +list format. >> + >> +User-space tools need to know the offset of list, phys and virt_addr >> +when computing the count of vmemmap regions. >> + >> +mmu_psize_def|(mmu_psize_def, shift) >> +------------------------------------ >> + >> +The size of a struct mmu_psize_def and the offset of mmu_psize_def's >> +member. >> + >> +Used in vtop translations. >> + >> +== >> +sh >> +== >> + >> +node_data|(node_data, MAX_NUMNODES) >> +----------------------------------- >> + >> +See above. >> + >> +X2TLB >> +----- >> + >> +Indicates whether the crash kernel enables SH extended mode. >> -- >> 2.17.1 >> > >
