netdev - Re: [PATCH bpf-next] selftests/xsk: fix munmap for hugepage allocated umem

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Date:   Thu, 20 Apr 2023 10:12:21 +0200
From:   Magnus Karlsson <magnus.karlsson@...il.com>
To:     Kal Cutter Conley <kal.conley@...tris.com>
Cc:     magnus.karlsson@...el.com, bjorn@...nel.org, ast@...nel.org,
        daniel@...earbox.net, netdev@...r.kernel.org,
        maciej.fijalkowski@...el.com, tirthendu.sarkar@...el.com,
        bpf@...r.kernel.org
Subject: Re: [PATCH bpf-next] selftests/xsk: fix munmap for hugepage allocated umem

On Thu, 20 Apr 2023 at 00:01, Kal Cutter Conley <kal.conley@...tris.com> wrote:
>
> > @@ -1286,16 +1287,19 @@ static void thread_common_ops(struct test_spec *test, struct ifobject *ifobject)
> >         u64 umem_sz = ifobject->umem->num_frames * ifobject->umem->frame_size;
> >         int mmap_flags = MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE;
> >         LIBBPF_OPTS(bpf_xdp_query_opts, opts);
> > +       off_t mmap_offset = 0;
> >         void *bufs;
> >         int ret;
> >
> > -       if (ifobject->umem->unaligned_mode)
> > +       if (ifobject->umem->unaligned_mode) {
> >                 mmap_flags |= MAP_HUGETLB;
> > +               mmap_offset = MAP_HUGE_2MB;
> > +       }
>
> MAP_HUGE_2MB should be ORed into mmap_flags. The offset argument
> should be zero for MAP_ANONYMOUS mappings. The tests may still fail if
> the default hugepage size is not 2MB.

You are correct that it should go into the flags field. Misread the
man page so will send a fix.

It was a conscious decision to require a hugepage size of 2M. I want
it to fail if you do not have it since the rest of the code will not
work if you are using some other size. Yes, it is possible to discover
what hugepage sizes exist and act on that, but I want to keep the code
simple.

> >
> >         if (ifobject->shared_umem)
> >                 umem_sz *= 2;
> >
> > -       bufs = mmap(NULL, umem_sz, PROT_READ | PROT_WRITE, mmap_flags, -1, 0);
> > +       bufs = mmap(NULL, umem_sz, PROT_READ | PROT_WRITE, mmap_flags, -1, mmap_offset);
> >         if (bufs == MAP_FAILED)
> >                 exit_with_error(errno);
> >
>
> -Kal