From: Brian Geffon <bgeffon@xxxxxxxxxx> Subject: selftests: add a MREMAP_DONTUNMAP selftest for shmem This test extends the current mremap tests to validate that the MREMAP_DONTUNMAP operation can be performed on shmem mappings. Link: https://lkml.kernel.org/r/20210323182520.2712101-3-bgeffon@xxxxxxxxxx Signed-off-by: Brian Geffon <bgeffon@xxxxxxxxxx> Cc: Axel Rasmussen <axelrasmussen@xxxxxxxxxx> Cc: Lokesh Gidra <lokeshgidra@xxxxxxxxxx> Cc: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx> Cc: Peter Xu <peterx@xxxxxxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Cc: "Michael S . Tsirkin" <mst@xxxxxxxxxx> Cc: Brian Geffon <bgeffon@xxxxxxxxxx> Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx> Cc: Vlastimil Babka <vbabka@xxxxxxx> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx> Cc: Sonny Rao <sonnyrao@xxxxxxxxxx> Cc: Minchan Kim <minchan@xxxxxxxxxx> Cc: "Kirill A . Shutemov" <kirill@xxxxxxxxxxxxx> Cc: Dmitry Safonov <dima@xxxxxxxxxx> Cc: Michael Kerrisk <mtk.manpages@xxxxxxxxx> Cc: Alejandro Colomar <alx.manpages@xxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- tools/testing/selftests/vm/mremap_dontunmap.c | 52 ++++++++++++++++ 1 file changed, 52 insertions(+) --- a/tools/testing/selftests/vm/mremap_dontunmap.c~selftests-add-a-mremap_dontunmap-selftest-for-shmem +++ a/tools/testing/selftests/vm/mremap_dontunmap.c @@ -127,6 +127,57 @@ static void mremap_dontunmap_simple() "unable to unmap source mapping"); } +// This test validates that MREMAP_DONTUNMAP on a shared mapping works as expected. +static void mremap_dontunmap_simple_shmem() +{ + unsigned long num_pages = 5; + + int mem_fd = memfd_create("memfd", MFD_CLOEXEC); + BUG_ON(mem_fd < 0, "memfd_create"); + + BUG_ON(ftruncate(mem_fd, num_pages * page_size) < 0, + "ftruncate"); + + void *source_mapping = + mmap(NULL, num_pages * page_size, PROT_READ | PROT_WRITE, + MAP_FILE | MAP_SHARED, mem_fd, 0); + BUG_ON(source_mapping == MAP_FAILED, "mmap"); + + BUG_ON(close(mem_fd) < 0, "close"); + + memset(source_mapping, 'a', num_pages * page_size); + + // Try to just move the whole mapping anywhere (not fixed). + void *dest_mapping = + mremap(source_mapping, num_pages * page_size, num_pages * page_size, + MREMAP_DONTUNMAP | MREMAP_MAYMOVE, NULL); + if (dest_mapping == MAP_FAILED && errno == EINVAL) { + // Old kernel which doesn't support MREMAP_DONTUNMAP on shmem. + BUG_ON(munmap(source_mapping, num_pages * page_size) == -1, + "unable to unmap source mapping"); + return; + } + + BUG_ON(dest_mapping == MAP_FAILED, "mremap"); + + // Validate that the pages have been moved, we know they were moved if + // the dest_mapping contains a's. + BUG_ON(check_region_contains_byte + (dest_mapping, num_pages * page_size, 'a') != 0, + "pages did not migrate"); + + // Because the region is backed by shmem, we will actually see the same + // memory at the source location still. + BUG_ON(check_region_contains_byte + (source_mapping, num_pages * page_size, 'a') != 0, + "source should have no ptes"); + + BUG_ON(munmap(dest_mapping, num_pages * page_size) == -1, + "unable to unmap destination mapping"); + BUG_ON(munmap(source_mapping, num_pages * page_size) == -1, + "unable to unmap source mapping"); +} + // This test validates MREMAP_DONTUNMAP will move page tables to a specific // destination using MREMAP_FIXED, also while validating that the source // remains intact. @@ -300,6 +351,7 @@ int main(void) BUG_ON(page_buffer == MAP_FAILED, "unable to mmap a page."); mremap_dontunmap_simple(); + mremap_dontunmap_simple_shmem(); mremap_dontunmap_simple_fixed(); mremap_dontunmap_partial_mapping(); mremap_dontunmap_partial_mapping_overwrite(); _
