I am trying to decipher how to use /proc/pid/pagemap to get the physical address of a given set of pages. Suppose from the /proc/pid/maps, I get the virtual address afa2d000-afa42000 which corresponds to the heap. My question is how do I use this info to traverse the pagemap file and find the physical page frames correspond to the address afa2d000-afa42000.
The /proc/pid/pagemap entry is in binary format. Is there any tools to help parsing of this file?
Try this http://www.eqware.net/Articles/CapturingProcessMemoryUsageUnderLinux/ It can parse the pagemap for you, for example, if the virtual address you are interested is in the heap which is 0x055468 : = 0004c000-0005a000 rw-p 00000000 00:00 0 [heap] : 86000000000FD6D6 : 0600000000000000
: 0600000000000000
: 86000000000FE921
: 86000000000FE922
: 0600000000000000
: 86000000000FD5AD
: 86000000000FD6D4
: 86000000000FD5F8
: 86000000000FD5FA =>9th
Suppose the page size as 4KB, and (0x055468 - 0x4c000) mod 4K = 9, So the page frame number of your page is the 9th page frames ==> : 86000000000FD5FA So the physical pfn is 0xFD5FA000 (take the last 55 bits and times page size) plus the offset: ( 0x055468 - 0x4c000 - 9*4K) = 0x468 ==> the physical addr is 0xFD5FA000 + 0x468 = 0xFD5FA468
I hope this link will help. It's a very simple tool, and determining the address you need to access is very simple: http://fivelinesofcode.blogspot.com/2014/03/how-to-translate-virtual-to-physical.html
Linux kernel documentation
Linux kernel doc describing the format: https://github.com/torvalds/linux/blob/v4.9/Documentation/vm/pagemap.txt
* Bits 0-54 page frame number (PFN) if present * Bits 0-4 swap type if swapped * Bits 5-54 swap offset if swapped * Bit 55 pte is soft-dirty (see Documentation/vm/soft-dirty.txt) * Bit 56 page exclusively mapped (since 4.2) * Bits 57-60 zero * Bit 61 page is file-page or shared-anon (since 3.5) * Bit 62 page swapped * Bit 63 page present C parser function
#define _XOPEN_SOURCE 700 #include /* open */ #include /* uint64_t */ #include /* size_t */ #include /* pread, sysconf */ typedef struct { uint64_t pfn : 54; unsigned int soft_dirty : 1; unsigned int file_page : 1; unsigned int swapped : 1; unsigned int present : 1; } PagemapEntry; /* Parse the pagemap entry for the given virtual address. * * @param[out] entry the parsed entry * @param[in] pagemap_fd file descriptor to an open /proc/pid/pagemap file * @param[in] vaddr virtual address to get entry for * @return 0 for success, 1 for failure */ int pagemap_get_entry(PagemapEntry *entry, int pagemap_fd, uintptr_t vaddr) { size_t nread; ssize_t ret; uint64_t data; nread = 0; while (nread pfn = data & (((uint64_t)1 soft_dirty = (data >> 54) & 1; entry->file_page = (data >> 61) & 1; entry->swapped = (data >> 62) & 1; entry->present = (data >> 63) & 1; return 0; } Example runnable programs using it:
In case folks want to do this from Rust, I've added a Rust implementation so you can easily navigate /proc/$pid/maps and /proc/$pid/pagemap: https://crates.io/crates/vm-info