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? > > 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 >
