From: John Hubbard jhubbard@nvidia.com
[ Upstream commit 64801d19eba156170340c76f70ade743defcb8ce ]
The MAP_HUGETLB ("-H" option) of gup_benchmark fails:
$ sudo ./gup_benchmark -H mmap: Invalid argument
This is because gup_benchmark.c is passing in a file descriptor to mmap(), but the fd came from opening up the /dev/zero file. This confuses the mmap syscall implementation, which thinks that, if the caller did not specify MAP_ANONYMOUS, then the file must be a huge page file. So it attempts to verify that the file really is a huge page file, as you can see here:
ksys_mmap_pgoff() { if (!(flags & MAP_ANONYMOUS)) { retval = -EINVAL; if (unlikely(flags & MAP_HUGETLB && !is_file_hugepages(file))) goto out_fput; /* THIS IS WHERE WE END UP */
else if (flags & MAP_HUGETLB) { ...proceed normally, /dev/zero is ok here...
...and of course is_file_hugepages() returns "false" for the /dev/zero file.
The problem is that the user space program, gup_benchmark.c, really just wants anonymous memory here. The simplest way to get that is to pass MAP_ANONYMOUS whenever MAP_HUGETLB is specified, so that's what this patch does.
Link: http://lkml.kernel.org/r/20191021212435.398153-2-jhubbard@nvidia.com Signed-off-by: John Hubbard jhubbard@nvidia.com Reviewed-by: Andrew Morton akpm@linux-foundation.org Reviewed-by: Jérôme Glisse jglisse@redhat.com Cc: Keith Busch keith.busch@intel.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- tools/testing/selftests/vm/gup_benchmark.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/tools/testing/selftests/vm/gup_benchmark.c b/tools/testing/selftests/vm/gup_benchmark.c index c0534e298b512..8e9929ce64cdb 100644 --- a/tools/testing/selftests/vm/gup_benchmark.c +++ b/tools/testing/selftests/vm/gup_benchmark.c @@ -71,7 +71,7 @@ int main(int argc, char **argv) flags |= MAP_SHARED; break; case 'H': - flags |= MAP_HUGETLB; + flags |= (MAP_HUGETLB | MAP_ANONYMOUS); break; default: return -1;