Re: [PATCH v8 3/4] mm/madvise: introduce process_madvise() syscall: an external memory hinting API

On Fri, Aug 28, 2020 at 9:27 PM Jens Axboe [off-list ref] wrote:

On 8/28/20 12:24 PM, Jens Axboe wrote:

quoted

quoted

@@ -1683,8 +1683,13 @@ ssize_t import_iovec(int type, const struct

iovec __user * uvector,
 {
        ssize_t n;
        struct iovec *p;
-       n = rw_copy_check_uvector(type, uvector, nr_segs, fast_segs,
-                                 *iov, &p);
+
+       if (in_compat_syscall())
+               n = compat_rw_copy_check_uvector(type, uvector, nr_segs,
+                                                fast_segs, *iov, &p);
+       else
+               n = rw_copy_check_uvector(type, uvector, nr_segs,
+                                         fast_segs, *iov, &p);
        if (n < 0) {
                if (p != *iov)
                        kfree(p);

Doesn't work for the async case, where you want to be holding on to the
allocated iovec. But in general I think it's a good helper for the sync
case, which is by far the majority.

Nevermind, I'm an idiot for reading this totally wrong.

I think you are right about the need to pick the compat vs native
behavior based on req->ctx->compat instead of in_compat_syscall()
inside of io_import_iovec().

That one can probably call a lower-level version and when all other
callers get changed to calling

ssize_t import_iovec(int type, const struct iovec __user * uvector,
                 unsigned nr_segs, unsigned fast_segs,
                 struct iovec **iov, struct iov_iter *i)
{
       return __import_iovec(type, uvector, nr_segs, fast_segs, iov,
i, in_compat_syscall());
}

      Arnd