[PATCH 1/4] KVM: selftests: Use MMIO to trigger emulation in emulator_error_test

[David Matlack <dmatlack@google.com>]

Use MMIO to force KVM to emulate the flds isntruction in
emulator_error_test, rather than relying on KVM_CAP_SMALLER_MAXPHYADDR.

KVM_CAP_SMALLER_MAXPHYADDR is not enabled by default when TDP is
enabled. So developers that run all selftests against KVM in its default
configuration do not get test coverage of
KVM_CAP_EXIT_ON_EMULATION_FAILURE.

When TDP is disabled, KVM_CAP_SMALLER_MAXPHYADDR is enabled by default,
but emulator_error_test actually fails because KVM does not need to
emulate flds.  i.e. The test fails to induce and emulation failure.

Fixes: 39bbcc3a4e39 ("selftests: kvm: Allows userspace to handle emulation errors.")
Signed-off-by: David Matlack <dmatlack@google.com>
---
 .../kvm/x86_64/emulator_error_test.c          | 36 ++++++-------------
 1 file changed, 10 insertions(+), 26 deletions(-)

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 236e11755ba6..2dff57991d31 100644
--- a/tools/testing/selftests/kvm/x86_64/emulator_error_test.c
+++ b/tools/testing/selftests/kvm/x86_64/emulator_error_test.c
@@ -11,18 +11,12 @@
 #include "kvm_util.h"
 #include "vmx.h"
 
-#define MAXPHYADDR 36
-
-#define MEM_REGION_GVA	0x0000123456789000
-#define MEM_REGION_GPA	0x0000000700000000
-#define MEM_REGION_SLOT	10
-#define MEM_REGION_SIZE PAGE_SIZE
+#define MMIO_REGION_GPA	0x700000000
+#define MMIO_REGION_GVA	0x700000000
 
 static void guest_code(void)
 {
-	__asm__ __volatile__("flds (%[addr])"
-			     :: [addr]"r"(MEM_REGION_GVA));
-
+	__asm__ __volatile__("flds (%[addr])" :: [addr]"r"(MMIO_REGION_GVA));
 	GUEST_DONE();
 }
 
@@ -152,34 +146,24 @@ int main(int argc, char *argv[])
 {
 	struct kvm_vcpu *vcpu;
 	struct kvm_vm *vm;
-	uint64_t gpa, pte;
-	uint64_t *hva;
 	int rc;
 
 	/* Tell stdout not to buffer its content */
 	setbuf(stdout, NULL);
 
-	TEST_REQUIRE(kvm_has_cap(KVM_CAP_SMALLER_MAXPHYADDR));
-
 	vm = vm_create_with_one_vcpu(&vcpu, guest_code);
 
-	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");
 	vm_enable_cap(vm, KVM_CAP_EXIT_ON_EMULATION_FAILURE, 1);
 
-	vm_userspace_mem_region_add(vm, VM_MEM_SRC_ANONYMOUS,
-				    MEM_REGION_GPA, MEM_REGION_SLOT,
-				    MEM_REGION_SIZE / PAGE_SIZE, 0);
-	gpa = vm_phy_pages_alloc(vm, MEM_REGION_SIZE / PAGE_SIZE,
-				 MEM_REGION_GPA, MEM_REGION_SLOT);
-	TEST_ASSERT(gpa == MEM_REGION_GPA, "Failed vm_phy_pages_alloc\n");
-	virt_map(vm, MEM_REGION_GVA, MEM_REGION_GPA, 1);
-	hva = addr_gpa2hva(vm, MEM_REGION_GPA);
-	memset(hva, 0, PAGE_SIZE);
-	pte = vm_get_page_table_entry(vm, vcpu, MEM_REGION_GVA);
-	vm_set_page_table_entry(vm, vcpu, MEM_REGION_GVA, pte | (1ull << 36));
+	/*
+	 * Create a virtual mapping so the guest can access MMIO_REGION_GPA.
+	 * MMIO_REGION_GPA is not mapped by a memslot so KVM will treat the
+	 * access as MMIO and attempt to emulate the flds instruction, which
+	 * will then generate an emulation error.
+	 */
+	virt_map(vm, MMIO_REGION_GVA, MMIO_REGION_GPA, 1);
 
 	vcpu_run(vcpu);
 	process_exit_on_emulation_error(vcpu);
-- 
2.38.0.rc1.362.ged0d419d3c-goog