KVM: selftests: Cache CPUID in struct kvm_vcpu

Cache a vCPU's CPUID information in "struct kvm_vcpu" to allow fixing the
mess where tests, often unknowingly, modify the global/static "cpuid"
allocated by kvm_get_supported_cpuid().

Add vcpu_init_cpuid() to handle stuffing an entirely different CPUID
model, e.g. during vCPU creation or when switching to the Hyper-V enabled
CPUID model.  Automatically refresh the cache on vcpu_set_cpuid() so that
any adjustments made by KVM are always reflected in the cache.  Drop
vcpu_get_cpuid() entirely to force tests to use the cache, and to allow
adding e.g. vcpu_get_cpuid_entry() in the future without creating a
conflicting set of APIs where vcpu_get_cpuid() does KVM_GET_CPUID2, but
vcpu_get_cpuid_entry() does not.

Opportunistically convert the VMX nested state test and KVM PV test to
manipulating the vCPU's CPUID (because it's easy), but use
vcpu_init_cpuid() for the Hyper-V features test and "emulator error" test
to effectively retain their current behavior as they're less trivial to
convert.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/20220614200707.3315957-19-seanjc@google.com

2 files changed, 27 insertions, 22 deletions

diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
index 49c189878af3..9889fe0d8919 100644
--- a/tools/testing/selftests/kvm/lib/kvm_util.c
+++ b/tools/testing/selftests/kvm/lib/kvm_util.c
@@ -472,6 +472,11 @@ kvm_userspace_memory_region_find(struct kvm_vm *vm, uint64_t start,
 	return &region->region;
 }
 
+__weak void vcpu_arch_free(struct kvm_vcpu *vcpu)
+{
+
+}
+
 /*
  * VM VCPU Remove
  *
@@ -501,6 +506,8 @@ static void vm_vcpu_rm(struct kvm_vm *vm, struct kvm_vcpu *vcpu)
 	TEST_ASSERT(!ret,  __KVM_SYSCALL_ERROR("close()", ret));
 
 	list_del(&vcpu->list);
+
+	vcpu_arch_free(vcpu);
 	free(vcpu);
 }
 
diff --git a/tools/testing/selftests/kvm/lib/x86_64/processor.c b/tools/testing/selftests/kvm/lib/x86_64/processor.c
index 4d383dee30b7..4cbcc333bba0 100644
--- a/tools/testing/selftests/kvm/lib/x86_64/processor.c
+++ b/tools/testing/selftests/kvm/lib/x86_64/processor.c
@@ -648,7 +648,7 @@ struct kvm_vcpu *vm_arch_vcpu_add(struct kvm_vm *vm, uint32_t vcpu_id,
 				     DEFAULT_GUEST_STACK_VADDR_MIN);
 
 	vcpu = __vm_vcpu_add(vm, vcpu_id);
-	vcpu_set_cpuid(vcpu, kvm_get_supported_cpuid());
+	vcpu_init_cpuid(vcpu, kvm_get_supported_cpuid());
 	vcpu_setup(vm, vcpu);
 
 	/* Setup guest general purpose registers */
@@ -669,11 +669,17 @@ struct kvm_vcpu *vm_arch_vcpu_recreate(struct kvm_vm *vm, uint32_t vcpu_id)
 {
 	struct kvm_vcpu *vcpu = __vm_vcpu_add(vm, vcpu_id);
 
-	vcpu_set_cpuid(vcpu, kvm_get_supported_cpuid());
+	vcpu_init_cpuid(vcpu, kvm_get_supported_cpuid());
 
 	return vcpu;
 }
 
+void vcpu_arch_free(struct kvm_vcpu *vcpu)
+{
+	if (vcpu->cpuid)
+		free(vcpu->cpuid);
+}
+
 /*
  * KVM Supported CPUID Get
  *
@@ -743,30 +749,22 @@ uint64_t kvm_get_feature_msr(uint64_t msr_index)
 	return buffer.entry.data;
 }
 
-struct kvm_cpuid2 *vcpu_get_cpuid(struct kvm_vcpu *vcpu)
+void vcpu_init_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid2 *cpuid)
 {
-	struct kvm_cpuid2 *cpuid;
-	int max_ent;
-	int rc = -1;
-
-	cpuid = allocate_kvm_cpuid2(MAX_NR_CPUID_ENTRIES);
-	max_ent = cpuid->nent;
+	TEST_ASSERT(cpuid != vcpu->cpuid, "@cpuid can't be the vCPU's CPUID");
 
-	for (cpuid->nent = 1; cpuid->nent <= max_ent; cpuid->nent++) {
-		rc = __vcpu_ioctl(vcpu, KVM_GET_CPUID2, cpuid);
-		if (!rc)
-			break;
-
-		TEST_ASSERT(rc == -1 && errno == E2BIG,
-			    "KVM_GET_CPUID2 should either succeed or give E2BIG: %d %d",
-			    rc, errno);
+	/* Allow overriding the default CPUID. */
+	if (vcpu->cpuid && vcpu->cpuid->nent < cpuid->nent) {
+		free(vcpu->cpuid);
+		vcpu->cpuid = NULL;
 	}
 
-	TEST_ASSERT(!rc, KVM_IOCTL_ERROR(KVM_GET_CPUID2, rc));
-	return cpuid;
-}
-
+	if (!vcpu->cpuid)
+		vcpu->cpuid = allocate_kvm_cpuid2(cpuid->nent);
 
+	memcpy(vcpu->cpuid, cpuid, kvm_cpuid2_size(cpuid->nent));
+	vcpu_set_cpuid(vcpu);
+}
 
 /*
  * Locate a cpuid entry.
@@ -1302,7 +1300,7 @@ void vcpu_set_hv_cpuid(struct kvm_vcpu *vcpu)
 		cpuid_full->nent = nent + cpuid_hv->nent;
 	}
 
-	vcpu_set_cpuid(vcpu, cpuid_full);
+	vcpu_init_cpuid(vcpu, cpuid_full);
 }
 
 struct kvm_cpuid2 *vcpu_get_supported_hv_cpuid(struct kvm_vcpu *vcpu)