KVM: selftests: Add and use helper to set vCPU's CPUID maxphyaddr

Add a helper to set a vCPU's guest.MAXPHYADDR, and use it in the test
that verifies the emulator returns an error on an unknown instruction
when KVM emulates in response to an EPT violation with a GPA that is
legal in hardware but illegal with respect to the guest's MAXPHYADDR.

Add a helper even though there's only a single user at this time.  Before
its removal, mmu_role_test also stuffed guest.MAXPHYADDR, and the helper
provides a small amount of clarity.

More importantly, this eliminates a set_cpuid() user and an instance of
modifying kvm_get_supported_cpuid()'s static "cpuid".

Signed-off-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/20220614200707.3315957-25-seanjc@google.com

3 files changed, 11 insertions, 9 deletions

diff --git a/tools/testing/selftests/kvm/include/x86_64/processor.h b/tools/testing/selftests/kvm/include/x86_64/processor.h
index 25b99eab7e71..a3d61807d223 100644
--- a/tools/testing/selftests/kvm/include/x86_64/processor.h
+++ b/tools/testing/selftests/kvm/include/x86_64/processor.h
@@ -658,6 +658,8 @@ static inline void vcpu_set_cpuid(struct kvm_vcpu *vcpu)
 	vcpu_ioctl(vcpu, KVM_GET_CPUID2, vcpu->cpuid);
 }
 
+void vcpu_set_cpuid_maxphyaddr(struct kvm_vcpu *vcpu, uint8_t maxphyaddr);
+
 void vcpu_set_or_clear_cpuid_feature(struct kvm_vcpu *vcpu,
 				     struct kvm_x86_cpu_feature feature,
 				     bool set);
diff --git a/tools/testing/selftests/kvm/lib/x86_64/processor.c b/tools/testing/selftests/kvm/lib/x86_64/processor.c
index 080480c397a4..27bf5dad6ec5 100644
--- a/tools/testing/selftests/kvm/lib/x86_64/processor.c
+++ b/tools/testing/selftests/kvm/lib/x86_64/processor.c
@@ -762,6 +762,14 @@ void vcpu_init_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid2 *cpuid)
 	vcpu_set_cpuid(vcpu);
 }
 
+void vcpu_set_cpuid_maxphyaddr(struct kvm_vcpu *vcpu, uint8_t maxphyaddr)
+{
+	struct kvm_cpuid_entry2 *entry = vcpu_get_cpuid_entry(vcpu, 0x80000008);
+
+	entry->eax = (entry->eax & ~0xff) | maxphyaddr;
+	vcpu_set_cpuid(vcpu);
+}
+
 void vcpu_set_or_clear_cpuid_feature(struct kvm_vcpu *vcpu,
 				     struct kvm_x86_cpu_feature feature,
 				     bool set)
diff --git a/tools/testing/selftests/kvm/x86_64/emulator_error_test.c b/tools/testing/selftests/kvm/x86_64/emulator_error_test.c
index d8dbed419638..236e11755ba6 100644
--- a/tools/testing/selftests/kvm/x86_64/emulator_error_test.c
+++ b/tools/testing/selftests/kvm/x86_64/emulator_error_test.c
@@ -150,8 +150,6 @@ static uint64_t process_ucall(struct kvm_vcpu *vcpu)
 
 int main(int argc, char *argv[])
 {
-	struct kvm_cpuid_entry2 *entry;
-	struct kvm_cpuid2 *cpuid;
 	struct kvm_vcpu *vcpu;
 	struct kvm_vm *vm;
 	uint64_t gpa, pte;
@@ -165,13 +163,7 @@ int main(int argc, char *argv[])
 
 	vm = vm_create_with_one_vcpu(&vcpu, guest_code);
 
-	cpuid = kvm_get_supported_cpuid();
-
-	entry = kvm_get_supported_cpuid_index(0x80000008, 0);
-	entry->eax = (entry->eax & 0xffffff00) | MAXPHYADDR;
-	set_cpuid(cpuid, entry);
-
-	vcpu_init_cpuid(vcpu, cpuid);
+	vcpu_set_cpuid_maxphyaddr(vcpu, MAXPHYADDR);
 
 	rc = kvm_check_cap(KVM_CAP_EXIT_ON_EMULATION_FAILURE);
 	TEST_ASSERT(rc, "KVM_CAP_EXIT_ON_EMULATION_FAILURE is unavailable");