Re: [PATCH v8 2/2] target/s390x: support PRNO_TRNG instruction

[Thomas Huth <thuth@redhat.com>]

On 21/09/2022 12.07, Jason A. Donenfeld wrote:
> In order for hosts running inside of TCG to initialize the kernel's
> random number generator, we should support the PRNO_TRNG instruction,
> backed in the usual way with the qemu_guest_getrandom helper. This is
> confirmed working on Linux 5.19.
> 
> Cc: Thomas Huth <thuth@redhat.com>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
> Cc: Richard Henderson <richard.henderson@linaro.org>
> Cc: Cornelia Huck <cohuck@redhat.com>
> Cc: Harald Freudenberger <freude@linux.ibm.com>
> Cc: Holger Dengler <dengler@linux.ibm.com>
> Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
> ---
>   target/s390x/gen-features.c      |  1 +
>   target/s390x/tcg/crypto_helper.c | 30 ++++++++++++++++++++++++++++++
>   2 files changed, 31 insertions(+)

Seems like this is even working fine with older Linux kernels ... your patch accidentally broke test_s390x_devices in tests/avocado/machine_s390_ccw_virtio.py: This test adds two virtio-rng devices to the guest, then ejects them to see whether /dev/hwrng will be gone ... which does not happen anymore with the prno-trng feature enabled :-)

I'm going to squash this one-liner to fix this issue:

diff a/tests/avocado/machine_s390_ccw_virtio.py b/tests/avocado/machine_s390_ccw_virtio.py
--- a/tests/avocado/machine_s390_ccw_virtio.py
+++ b/tests/avocado/machine_s390_ccw_virtio.py
@@ -66,6 +66,7 @@ def test_s390x_devices(self):
                           '-kernel', kernel_path,
                           '-initrd', initrd_path,
                           '-append', kernel_command_line,
+                         '-cpu', 'max,prno-trng=off',
                           '-device', 'virtio-net-ccw,devno=fe.1.1111',
                           '-device',
                           'virtio-rng-ccw,devno=fe.2.0000,max_revision=0,id=rn1',

  Thomas