[PATCH 1/3] KVM: selftests: Fix treating KVM_CAP_MAX_VCPU_ID as inclusive

[Dmytro Maluka <dmaluka@chromium.org>]

KVM_CAP_MAX_VCPU_ID is (confusingly) exclusive, i.e. the maximum allowed
vcpu_id value is KVM_CAP_MAX_VCPU_ID minus one.

Some tests in x86/max_vcpuid_cap_test.c and kvm/x86/set_boot_cpu_id.c
mistakenly treat it as inclusive, in particular, assume that setting
bsp_vcpu_id to KVM_CAP_MAX_VCPU_ID is valid and should succeed. Fix
those tests.

Fixes: 4b451a57809c ("KVM: selftests: Test max vCPU IDs corner cases")
Fixes: 438a496b9041 ("KVM: selftests: Test vCPU boot IDs above 2^32 and MAX_VCPU_ID")
Signed-off-by: Dmytro Maluka <dmaluka@chromium.org>
---
 .../selftests/kvm/x86/max_vcpuid_cap_test.c     | 17 ++++++++++-------
 .../testing/selftests/kvm/x86/set_boot_cpu_id.c |  4 ++--
 2 files changed, 12 insertions(+), 9 deletions(-)

diff --git a/tools/testing/selftests/kvm/x86/max_vcpuid_cap_test.c b/tools/testing/selftests/kvm/x86/max_vcpuid_cap_test.c
index 7e2bfb3c3f3b..43f16c052de4 100644
--- a/tools/testing/selftests/kvm/x86/max_vcpuid_cap_test.c
+++ b/tools/testing/selftests/kvm/x86/max_vcpuid_cap_test.c
@@ -30,22 +30,25 @@ int main(int argc, char *argv[])
 	if (kvm_has_cap(KVM_CAP_SET_BOOT_CPU_ID)) {
 		vm_ioctl(vm, KVM_SET_BOOT_CPU_ID, (void *)MAX_VCPU_ID);
 
-		/* Try setting KVM_CAP_MAX_VCPU_ID below BOOT_CPU_ID */
-		ret = __vm_enable_cap(vm, KVM_CAP_MAX_VCPU_ID, MAX_VCPU_ID - 1);
+		/* Try setting KVM_CAP_MAX_VCPU_ID below or equal to BOOT_CPU_ID */
+		ret = __vm_enable_cap(vm, KVM_CAP_MAX_VCPU_ID, MAX_VCPU_ID);
 		TEST_ASSERT(ret < 0,
-			    "Setting KVM_CAP_MAX_VCPU_ID below BOOT_CPU_ID should fail");
+			    "Setting KVM_CAP_MAX_VCPU_ID <= BOOT_CPU_ID should fail");
 	}
 
-	/* Set KVM_CAP_MAX_VCPU_ID */
-	vm_enable_cap(vm, KVM_CAP_MAX_VCPU_ID, MAX_VCPU_ID);
+	/*
+	 * Set KVM_CAP_MAX_VCPU_ID. Note: KVM_CAP_MAX_VCPU_ID is a misnomer,
+	 * it actually represents maximum vcpu_id plus one.
+	 */
+	vm_enable_cap(vm, KVM_CAP_MAX_VCPU_ID, MAX_VCPU_ID + 1);
 
 	/* Try to set KVM_CAP_MAX_VCPU_ID again */
-	ret = __vm_enable_cap(vm, KVM_CAP_MAX_VCPU_ID, MAX_VCPU_ID + 1);
+	ret = __vm_enable_cap(vm, KVM_CAP_MAX_VCPU_ID, MAX_VCPU_ID + 2);
 	TEST_ASSERT(ret < 0,
 		    "Setting KVM_CAP_MAX_VCPU_ID multiple times should fail");
 
 	/* Create vCPU with id beyond KVM_CAP_MAX_VCPU_ID cap */
-	ret = __vm_ioctl(vm, KVM_CREATE_VCPU, (void *)MAX_VCPU_ID);
+	ret = __vm_ioctl(vm, KVM_CREATE_VCPU, (void *)(MAX_VCPU_ID + 1));
 	TEST_ASSERT(ret < 0, "Creating vCPU with ID > MAX_VCPU_ID should fail");
 
 	/* Create vCPU with bits 63:32 != 0, but an otherwise valid id */
diff --git a/tools/testing/selftests/kvm/x86/set_boot_cpu_id.c b/tools/testing/selftests/kvm/x86/set_boot_cpu_id.c
index 8e3898646c69..1c4ebdf8e82c 100644
--- a/tools/testing/selftests/kvm/x86/set_boot_cpu_id.c
+++ b/tools/testing/selftests/kvm/x86/set_boot_cpu_id.c
@@ -39,8 +39,8 @@ static void test_set_invalid_bsp(struct kvm_vm *vm)
 	int r;
 
 	if (max_vcpu_id) {
-		r = __vm_ioctl(vm, KVM_SET_BOOT_CPU_ID, (void *)(max_vcpu_id + 1));
-		TEST_ASSERT(r == -1 && errno == EINVAL, "BSP with ID > MAX should fail");
+		r = __vm_ioctl(vm, KVM_SET_BOOT_CPU_ID, (void *)max_vcpu_id);
+		TEST_ASSERT(r == -1 && errno == EINVAL, "BSP with ID >= MAX should fail");
 	}
 
 	r = __vm_ioctl(vm, KVM_SET_BOOT_CPU_ID, (void *)(1L << 32));
-- 
2.55.0.508.g3f0d502094-goog