linux-kernel - [PATCH 2/5] KVM: selftests: Provide an API for getting a random bool from an RNG

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Date: Thu, 14 Mar 2024 11:54:55 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Paolo Bonzini <pbonzini@...hat.com>, Sean Christopherson <seanjc@...gle.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 2/5] KVM: selftests: Provide an API for getting a random bool
 from an RNG

Move memstress' random bool logic into common code to avoid reinventing
the wheel for basic yes/no decisions.  Provide an outer wrapper to handle
the basic/common case of just wanting a 50/50 chance of something
happening.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 tools/testing/selftests/kvm/include/test_util.h | 11 +++++++++++
 tools/testing/selftests/kvm/lib/memstress.c     |  2 +-
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/kvm/include/test_util.h b/tools/testing/selftests/kvm/include/test_util.h
index 4b78fb7e539e..3e473058849f 100644
--- a/tools/testing/selftests/kvm/include/test_util.h
+++ b/tools/testing/selftests/kvm/include/test_util.h
@@ -97,6 +97,17 @@ extern struct guest_random_state guest_rng;
 struct guest_random_state new_guest_random_state(uint32_t seed);
 uint32_t guest_random_u32(struct guest_random_state *state);
 
+static inline bool __guest_random_bool(struct guest_random_state *state,
+				       uint8_t percent)
+{
+	return (guest_random_u32(state) % 100) < percent;
+}
+
+static inline bool guest_random_bool(struct guest_random_state *state)
+{
+	return __guest_random_bool(state, 50);
+}
+
 static inline uint64_t guest_random_u64(struct guest_random_state *state)
 {
 	return ((uint64_t)guest_random_u32(state) << 32) | guest_random_u32(state);
diff --git a/tools/testing/selftests/kvm/lib/memstress.c b/tools/testing/selftests/kvm/lib/memstress.c
index f8bfb4988368..2d49a5643b71 100644
--- a/tools/testing/selftests/kvm/lib/memstress.c
+++ b/tools/testing/selftests/kvm/lib/memstress.c
@@ -76,7 +76,7 @@ void memstress_guest_code(uint32_t vcpu_idx)
 
 			addr = gva + (page * args->guest_page_size);
 
-			if (guest_random_u32(&rand_state) % 100 < args->write_percent)
+			if (__guest_random_bool(&rand_state, args->write_percent))
 				*(uint64_t *)addr = 0x0123456789ABCDEF;
 			else
 				READ_ONCE(*(uint64_t *)addr);
-- 
2.44.0.291.gc1ea87d7ee-goog