/*
* util_map_hint -- determine hint address for mmap()
*
* If PMEM_MMAP_HINT environment variable is not set, we let the system to pick
* the randomized mapping address. Otherwise, a user-defined hint address
* is used.
*
* ALSR in 64-bit Linux kernel uses 28-bit of randomness for mmap
* (bit positions 12-39), which means the base mapping address is randomized
* within [0..1024GB] range, with 4KB granularity. Assuming additional
* 1GB alignment, it results in 1024 possible locations.
*
* Configuring the hint address via PMEM_MMAP_HINT environment variable
* disables address randomization. In such case, the function will search for
* the first unused, properly aligned region of given size, above the specified
* address.
*/
char *
util_map_hint(size_t len, size_t req_align)
{
LOG(3, "len %zu req_align %zu", len, req_align);
char *addr;
/* choose the desired alignment based on the requested length */
size_t align = util_map_hint_align(len, req_align);
if (Mmap_no_random) {
LOG(4, "user-defined hint %p", (void *)Mmap_hint);
addr = util_map_hint_unused((void *)Mmap_hint, len, align);
} else {
/*
* Create dummy mapping to find an unused region of given size.
* Request for increased size for later address alignment.
* Use MAP_PRIVATE with read-only access to simulate
* zero cost for overcommit accounting. Note: MAP_NORESERVE
* flag is ignored if overcommit is disabled (mode 2).
*/
addr = mmap(NULL, len + align, PROT_READ,
MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
if (addr != MAP_FAILED) {
LOG(4, "system choice %p", addr);
munmap(addr, len + align);
addr = (char *)roundup((uintptr_t)addr, align);
}
}
LOG(4, "hint %p", addr);
return addr;
}
int
main(int argc, char *argv[])
{
START(argc, argv, "util_map_proc");
util_init();
if (argc < 3)
UT_FATAL("usage: %s maps_file len [len]...", argv[0]);
Sfile = argv[1];
for (int arg = 2; arg < argc; arg++) {
size_t len = (size_t)strtoull(argv[arg], NULL, 0);
size_t align = Ut_pagesize;
if (len >= 2 * GIGABYTE)
align = GIGABYTE;
else if (len >= 4 * MEGABYTE)
align = 2 * MEGABYTE;
void *h1 =
util_map_hint_unused((void *)TERABYTE, len, GIGABYTE);
void *h2 = util_map_hint(len, 0);
if (h1 != MAP_FAILED && h1 != NULL)
UT_ASSERTeq((uintptr_t)h1 & (GIGABYTE - 1), 0);
if (h2 != MAP_FAILED && h2 != NULL)
UT_ASSERTeq((uintptr_t)h2 & (align - 1), 0);
UT_OUT("len %zu: %p %p", len, h1, h2);
}
DONE(NULL);
}
/*
* util_map_hint -- determine hint address for mmap()
*
* If PMEM_MMAP_HINT environment variable is not set, we let the system to pick
* the randomized mapping address. Otherwise, a user-defined hint address
* is used.
*
* Windows Environment:
* XXX - Windows doesn't support large DAX pages yet, so there is
* no point in aligning for the same.
*
* Except for Windows Environment:
* ALSR in 64-bit Linux kernel uses 28-bit of randomness for mmap
* (bit positions 12-39), which means the base mapping address is randomized
* within [0..1024GB] range, with 4KB granularity. Assuming additional
* 1GB alignment, it results in 1024 possible locations.
*
* Configuring the hint address via PMEM_MMAP_HINT environment variable
* disables address randomization. In such case, the function will search for
* the first unused, properly aligned region of given size, above the
* specified address.
*/
static char *util_map_hint(size_t len, size_t req_align)
{
char *addr;
size_t align = 0;
char *e = NULL;
dprint(FD_IO, "DEBUG util_map_hint\n");
dprint(FD_IO, "len %zu req_align %zu\n", len, req_align);
/* choose the desired alignment based on the requested length */
align = util_map_hint_align(len, req_align);
e = getenv("PMEM_MMAP_HINT");
if (e) {
char *endp;
unsigned long long val = 0;
errno = 0;
val = strtoull(e, &endp, 16);
if (errno || endp == e) {
dprint(FD_IO, "Invalid PMEM_MMAP_HINT\n");
} else {
Mmap_hint = (void *)val;
Mmap_no_random = true;
dprint(FD_IO, "PMEM_MMAP_HINT set to %p\n", Mmap_hint);
}
}
if (Mmap_no_random) {
dprint(FD_IO, "user-defined hint %p\n", (void *)Mmap_hint);
addr = util_map_hint_unused((void *)Mmap_hint, len, align);
} else {
/*
* Create dummy mapping to find an unused region of given size.
* * Request for increased size for later address alignment.
*
* Windows Environment:
* Use MAP_NORESERVE flag to only reserve the range of pages
* rather than commit. We don't want the pages to be actually
* backed by the operating system paging file, as the swap
* file is usually too small to handle terabyte pools.
*
* Except for Windows Environment:
* Use MAP_PRIVATE with read-only access to simulate
* zero cost for overcommit accounting. Note: MAP_NORESERVE
* flag is ignored if overcommit is disabled (mode 2).
*/
#ifndef WIN32
addr = mmap(NULL, len + align, PROT_READ,
MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
#else
addr = mmap(NULL, len + align, PROT_READ,
MAP_PRIVATE|MAP_ANONYMOUS|MAP_NORESERVE, -1, 0);
#endif
if (addr != MAP_FAILED) {
dprint(FD_IO, "system choice %p\n", addr);
munmap(addr, len + align);
addr = (char *)roundup((uintptr_t)addr, align);
}
}
dprint(FD_IO, "hint %p\n", addr);
return addr;
}
