From: "Michael S. Tsirkin" <mst@xxxxxxxxxx> Subject: mm/gup_benchmark: handle gup failures Patch series "mm/get_user_pages_fast fixes, cleanups", v2. Turns out get_user_pages_fast and __get_user_pages_fast return different values on error when given a single page: __get_user_pages_fast returns 0. get_user_pages_fast returns either 0 or an error. Callers of get_user_pages_fast expect an error so fix it up to return an error consistently. Stress the difference between get_user_pages_fast and __get_user_pages_fast to make sure callers aren't confused. This patch (of 3): __gup_benchmark_ioctl does not handle the case where get_user_pages_fast fails: - a negative return code will cause a buffer overrun - returning with partial success will cause use of uninitialized memory. [akpm@xxxxxxxxxxxxxxxxxxxx: simplification] Link: http://lkml.kernel.org/r/1522962072-182137-3-git-send-email-mst@xxxxxxxxxx Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx> Reviewed-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> Cc: Huang Ying <ying.huang@xxxxxxxxx> Cc: Jonathan Corbet <corbet@xxxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: Thorsten Leemhuis <regressions@xxxxxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/gup_benchmark.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff -puN mm/gup_benchmark.c~mm-gup_benchmark-handle-gup-failures mm/gup_benchmark.c --- a/mm/gup_benchmark.c~mm-gup_benchmark-handle-gup-failures +++ a/mm/gup_benchmark.c @@ -23,7 +23,7 @@ static int __gup_benchmark_ioctl(unsigne struct page **pages; nr_pages = gup->size / PAGE_SIZE; - pages = kvmalloc(sizeof(void *) * nr_pages, GFP_KERNEL); + pages = kvzalloc(sizeof(void *) * nr_pages, GFP_KERNEL); if (!pages) return -ENOMEM; @@ -41,6 +41,8 @@ static int __gup_benchmark_ioctl(unsigne } nr = get_user_pages_fast(addr, nr, gup->flags & 1, pages + i); + if (nr <= 0) + break; i += nr; } end_time = ktime_get(); _