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Fri, 26 Jun 2026 14:59:12 -0700 (PDT) Date: Fri, 26 Jun 2026 14:59:12 -0700 In-Reply-To: <20260626214819.EC79B1F000E9@smtp.kernel.org> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260626213534.3866178-1-seanjc@google.com> <20260626213534.3866178-5-seanjc@google.com> <20260626214819.EC79B1F000E9@smtp.kernel.org> Message-ID: Subject: Re: [PATCH v8 04/20] KVM: selftests: Initialize the default/global pRNG during kvm_selftest_init() From: Sean Christopherson To: sashiko-reviews@lists.linux.dev Cc: kvm@vger.kernel.org, Marc Zyngier , Oliver Upton , kvmarm@lists.linux.dev Content-Type: text/plain; charset="us-ascii" On Fri, Jun 26, 2026, sashiko-bot@kernel.org wrote: > > diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c > > index 875030c22d07b..1016865d3f7a2 100644 > > --- a/tools/testing/selftests/kvm/lib/kvm_util.c > > +++ b/tools/testing/selftests/kvm/lib/kvm_util.c > > @@ -24,6 +24,13 @@ u32 kvm_random_seed; > > struct kvm_random_state kvm_rng; > > static u32 last_kvm_seed; > > > > +static void kvm_seed_rng(u32 seed) > > +{ > > + kvm_random_seed = last_kvm_seed = seed; > > + pr_info("Random seed: 0x%x\n", kvm_random_seed); > > + kvm_rng = new_kvm_random_state(kvm_random_seed); > > +} > > + > > [Severity: Medium] > Does making this function static prevent tests from reseeding the PRNG > early? > > If a test draws from kvm_rng before __vm_create() is called (for example, > generating gsi and vector at the start of main() in irq_test), the test > will use the initial seed from the constructor. > > Since kvm_seed_rng() is static and only automatically reseeded during > __vm_create(), how can developers override the seed to reproduce CI failures > for these pre-VM random variables? By hacking selftests. Yes, it's ugly, but AFAIK we haven't yet had a failure that's actually been dependent on the RNG seed, and plumbing in a way to set the seed for every test would be painful.