KVM: selftests: Add a test for KVM_CAP_EXIT_ON_EMULATION_FAILURE

Add a selftest to exercise the KVM_CAP_EXIT_ON_EMULATION_FAILURE
capability.

This capability is also exercised through
smaller_maxphyaddr_emulation_test, but that test requires
allow_smaller_maxphyaddr=Y, which is off by default on Intel when ept=Y
and unconditionally disabled on AMD when npt=Y. This new test ensures
that KVM_CAP_EXIT_ON_EMULATION_FAILURE is exercised independent of
allow_smaller_maxphyaddr.
Signed-off-by: David Matlack <dmatlack@google.com>
Link: https://lore.kernel.org/r/20221102184654.282799-11-dmatlack@google.comSigned-off-by: Sean Christopherson <seanjc@google.com>

tools/testing/selftests/kvm/.gitignore

@@ -17,6 +17,7 @@
 /x86_64/cr4_cpuid_sync_test
 /x86_64/debug_regs
 /x86_64/evmcs_test
+/x86_64/exit_on_emulation_failure_test
 /x86_64/fix_hypercall_test
 /x86_64/get_msr_index_features
 /x86_64/kvm_clock_test

tools/testing/selftests/kvm/Makefile

@@ -82,6 +82,7 @@ TEST_GEN_PROGS_x86_64 = x86_64/cpuid_test
 TEST_GEN_PROGS_x86_64 += x86_64/cr4_cpuid_sync_test
 TEST_GEN_PROGS_x86_64 += x86_64/get_msr_index_features
 TEST_GEN_PROGS_x86_64 += x86_64/evmcs_test
+TEST_GEN_PROGS_x86_64 += x86_64/exit_on_emulation_failure_test
 TEST_GEN_PROGS_x86_64 += x86_64/fix_hypercall_test
 TEST_GEN_PROGS_x86_64 += x86_64/hyperv_clock
 TEST_GEN_PROGS_x86_64 += x86_64/hyperv_cpuid

tools/testing/selftests/kvm/x86_64/exit_on_emulation_failure_test.c

+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2022, Google LLC.
+ *
+ * Test for KVM_CAP_EXIT_ON_EMULATION_FAILURE.
+ */
+
+#define _GNU_SOURCE /* for program_invocation_short_name */
+
+#include "flds_emulation.h"
+
+#include "test_util.h"
+
+#define MMIO_GPA	0x700000000
+#define MMIO_GVA	MMIO_GPA
+
+static void guest_code(void)
+{
+	/* Execute flds with an MMIO address to force KVM to emulate it. */
+	flds(MMIO_GVA);
+	GUEST_DONE();
+}
+
+int main(int argc, char *argv[])
+{
+	struct kvm_vcpu *vcpu;
+	struct kvm_vm *vm;
+
+	/* Tell stdout not to buffer its content */
+	setbuf(stdout, NULL);
+
+	TEST_REQUIRE(kvm_has_cap(KVM_CAP_EXIT_ON_EMULATION_FAILURE));
+
+	vm = vm_create_with_one_vcpu(&vcpu, guest_code);
+	vm_enable_cap(vm, KVM_CAP_EXIT_ON_EMULATION_FAILURE, 1);
+	virt_map(vm, MMIO_GVA, MMIO_GPA, 1);
+
+	vcpu_run(vcpu);
+	handle_flds_emulation_failure_exit(vcpu);
+	vcpu_run(vcpu);
+	ASSERT_EQ(get_ucall(vcpu, NULL), UCALL_DONE);
+
+	kvm_vm_free(vm);
+	return 0;
+}