KVM: selftests: Load XSAVE state into untouched vCPU during state test

Expand x86's state test to load XSAVE state into a "dummy" vCPU prior to
KVM_SET_CPUID2, and again with an empty guest CPUID model.  Except for
off-by-default features, i.e. AMX, KVM's ABI for KVM_SET_XSAVE is that
userspace is allowed to load xfeatures so long as they are supported by
the host.  This is a regression test for a combination of KVM bugs where
the state saved by KVM_GET_XSAVE{2} could not be loaded via KVM_SET_XSAVE
if the saved xstate_bv would load guest-unsupported xfeatures.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20230928001956.924301-5-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/tools/testing/selftests/kvm/x86_64/state_test.c b/tools/testing/selftests/kvm/x86_64/state_test.c
index df3e93d..115b2cd 100644 (file)
--- a/tools/testing/selftests/kvm/x86_64/state_test.c
+++ b/tools/testing/selftests/kvm/x86_64/state_test.c
@@ -231,9 +231,9 @@ static void __attribute__((__flatten__)) guest_code(void *arg)
 int main(int argc, char *argv[])
 {
        vm_vaddr_t nested_gva = 0;
-
+       struct kvm_cpuid2 empty_cpuid = {};
        struct kvm_regs regs1, regs2;
-       struct kvm_vcpu *vcpu;
+       struct kvm_vcpu *vcpu, *vcpuN;
        struct kvm_vm *vm;
        struct kvm_x86_state *state;
        struct ucall uc;
@@ -286,6 +286,21 @@ int main(int argc, char *argv[])
                /* Restore state in a new VM.  */
                vcpu = vm_recreate_with_one_vcpu(vm);
                vcpu_load_state(vcpu, state);
+
+               /*
+                * Restore XSAVE state in a dummy vCPU, first without doing
+                * KVM_SET_CPUID2, and then with an empty guest CPUID.  Except
+                * for off-by-default xfeatures, e.g. AMX, KVM is supposed to
+                * allow KVM_SET_XSAVE regardless of guest CPUID.  Manually
+                * load only XSAVE state, MSRs in particular have a much more
+                * convoluted ABI.
+                */
+               vcpuN = __vm_vcpu_add(vm, vcpu->id + 1);
+               vcpu_xsave_set(vcpuN, state->xsave);
+
+               vcpu_init_cpuid(vcpuN, &empty_cpuid);
+               vcpu_xsave_set(vcpuN, state->xsave);
+
                kvm_x86_state_cleanup(state);
 
                memset(&regs2, 0, sizeof(regs2));