On Tue, Mar 26, 2024 at 3:32 PM David Hildenbrand <david@xxxxxxxxxx> wrote: > > Let's add a simple reproducer for a scenario where GUP-fast could succeed > on secretmem folios, making vmsplice() succeed instead of failing. The > reproducer is based on a reproducer [1] by Miklos Szeredi. > > We want to perform two tests: vmsplice() when a fresh page was just > faulted in, and vmsplice() on an existing page after munmap() that > would drain certain LRU caches/batches in the kernel. > > In an ideal world, we could use fallocate(FALLOC_FL_PUNCH_HOLE) / > MADV_REMOVE to remove any existing page. As that is currently not > possible, run the test before any other tests that would allocate memory > in the secretmem fd. > > Perform the ftruncate() only once, and check the return value. > > [1] https://lkml.kernel.org/r/CAJfpegt3UCsMmxd0taOY11Uaw5U=eS1fE5dn0wZX3HF0oy8-oQ@xxxxxxxxxxxxxx > > Signed-off-by: David Hildenbrand <david@xxxxxxxxxx> > --- > tools/testing/selftests/mm/memfd_secret.c | 51 ++++++++++++++++++++++- > 1 file changed, 49 insertions(+), 2 deletions(-) > > diff --git a/tools/testing/selftests/mm/memfd_secret.c b/tools/testing/selftests/mm/memfd_secret.c > index 9b298f6a04b3..9a0597310a76 100644 > --- a/tools/testing/selftests/mm/memfd_secret.c > +++ b/tools/testing/selftests/mm/memfd_secret.c > @@ -20,6 +20,7 @@ > #include <unistd.h> > #include <errno.h> > #include <stdio.h> > +#include <fcntl.h> > > #include "../kselftest.h" > > @@ -83,6 +84,45 @@ static void test_mlock_limit(int fd) > pass("mlock limit is respected\n"); > } > > +static void test_vmsplice(int fd, const char *desc) > +{ > + ssize_t transferred; > + struct iovec iov; > + int pipefd[2]; > + char *mem; > + > + if (pipe(pipefd)) { > + fail("pipe failed: %s\n", strerror(errno)); > + return; > + } > + > + mem = mmap(NULL, page_size, prot, mode, fd, 0); > + if (mem == MAP_FAILED) { > + fail("Unable to mmap secret memory\n"); > + goto close_pipe; > + } > + > + /* > + * vmsplice() may use GUP-fast, which must also fail. Prefault the > + * page table, so GUP-fast could find it. > + */ > + memset(mem, PATTERN, page_size); Shouldn't the non-prefault case be tested as well? Thanks, Miklos
