Re: [RFC PATCH bpf-next 5/5] selftests/bpf: get_reg_val test exercising fxsave fetch

[Dave Marchevsky <davemarchevsky@fb.com>]

On 5/12/22 3:43 AM, Dave Marchevsky wrote:   
> Add a test which calls bpf_get_reg_val with an xmm reg after forcing fpu
> state save. The test program writes to %xmm10, then calls a BPF program
> which forces fpu save and calls bpf_get_reg_val. This guarantees that
> !fpregs_state_valid check will succeed, forcing bpf_get_reg_val to fetch
> %xmm10's value from task's fpu state.
> 
> A bpf_testmod_save_fpregs kfunc helper is added to bpf_testmod to enable
> 'force fpu save'. Existing bpf_dummy_ops test infra is extended to
> support calling the kfunc.
> 
> unload_bpf_testmod would often fail with -EAGAIN when running the test
> added in this patch, so a single retry w/ 20ms sleep is added.
> 
> Signed-off-by: Dave Marchevsky <davemarchevsky@fb.com>
> ---
>  include/linux/bpf.h                           |  1 +
>  kernel/trace/bpf_trace.c                      |  2 +-
>  net/bpf/bpf_dummy_struct_ops.c                | 13 ++++++
>  .../selftests/bpf/bpf_testmod/bpf_testmod.c   | 13 ++++++
>  tools/testing/selftests/bpf/prog_tests/usdt.c | 42 +++++++++++++++++++
>  .../selftests/bpf/progs/test_urandom_usdt.c   | 24 +++++++++++
>  tools/testing/selftests/bpf/test_progs.c      |  7 ++++
>  7 files changed, 101 insertions(+), 1 deletion(-)

This series wasn't based on latest bpf-next. After rebase, this test
causes kernel panic. Investigating, but patches are still worth a
look.