[PATCH v7 17/19] KVM: selftests: Query module param to detect FEP in MSR filtering test

Sean Christopherson
2023-11-08T00:32:14Z

Add a helper to detect KVM support for forced emulation by querying the
module param, and use the helper to detect support for the MSR filtering
test instead of throwing a noodle/NOP at KVM to see if it sticks.

Cc: Aaron Lewis <aaronlewis@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
.../selftests/kvm/include/x86_64/processor.h | 5 ++++
.../kvm/x86_64/userspace_msr_exit_test.c | 27 +++++++------------
2 files changed, 14 insertions(+), 18 deletions(-)

diff --git a/tools/testing/selftests/kvm/include/x86_64/processor.h b/tools/testing/selftests/kvm/include/x86_64/processor.h
index c261e0941dfe..8a404faafb21 100644
--- a/tools/testing/selftests/kvm/include/x86_64/processor.h
+++ b/tools/testing/selftests/kvm/include/x86_64/processor.h
@@ -1221,6 +1221,11 @@ static inline bool kvm_is_pmu_enabled(void)
return get_kvm_param_bool("enable_pmu");
}

+static inline bool kvm_is_forced_emulation_enabled(void)
+{
+ return !!get_kvm_param_integer("force_emulation_prefix");
+}
+
uint64_t *__vm_get_page_table_entry(struct kvm_vm *vm, uint64_t vaddr,
int *level);
uint64_t *vm_get_page_table_entry(struct kvm_vm *vm, uint64_t vaddr);
diff --git a/tools/testing/selftests/kvm/x86_64/userspace_msr_exit_test.c b/tools/testing/selftests/kvm/x86_64/userspace_msr_exit_test.c
index 3533dc2fbfee..9e12dbc47a72 100644
--- a/tools/testing/selftests/kvm/x86_64/userspace_msr_exit_test.c
+++ b/tools/testing/selftests/kvm/x86_64/userspace_msr_exit_test.c
@@ -14,8 +14,7 @@

/* Forced emulation prefix, used to invoke the emulator unconditionally. */
#define KVM_FEP "ud2; .byte 'k', 'v', 'm';"
-#define KVM_FEP_LENGTH 5
-static int fep_available = 1;
+static bool fep_available;

#define MSR_NON_EXISTENT 0x474f4f00

@@ -260,13 +259,6 @@ static void guest_code_filter_allow(void)
GUEST_ASSERT(data == 2);
GUEST_ASSERT(guest_exception_count == 0);

- /*
- * Test to see if the instruction emulator is available (ie: the module
- * parameter 'kvm.force_emulation_prefix=1' is set). This instruction
- * will #UD if it isn't available.
- */
- __asm__ __volatile__(KVM_FEP "nop");
-
if (fep_available) {
/* Let userspace know we aren't done. */
GUEST_SYNC(0);
@@ -388,12 +380,6 @@ static void guest_fep_gp_handler(struct ex_regs *regs)
&em_wrmsr_start, &em_wrmsr_end);
}

-static void guest_ud_handler(struct ex_regs *regs)
-{
- fep_available = 0;
- regs->rip += KVM_FEP_LENGTH;
-}
-
static void check_for_guest_assert(struct kvm_vcpu *vcpu)
{
struct ucall uc;
@@ -531,9 +517,11 @@ static void test_msr_filter_allow(void)
{
struct kvm_vcpu *vcpu;
struct kvm_vm *vm;
+ uint64_t cmd;
int rc;

vm = vm_create_with_one_vcpu(&vcpu, guest_code_filter_allow);
+ sync_global_to_guest(vm, fep_available);

rc = kvm_check_cap(KVM_CAP_X86_USER_SPACE_MSR);
TEST_ASSERT(rc, "KVM_CAP_X86_USER_SPACE_MSR is available");
@@ -561,11 +549,11 @@ static void test_msr_filter_allow(void)
run_guest_then_process_wrmsr(vcpu, MSR_NON_EXISTENT);
run_guest_then_process_rdmsr(vcpu, MSR_NON_EXISTENT);

- vm_install_exception_handler(vm, UD_VECTOR, guest_ud_handler);
vcpu_run(vcpu);
- vm_install_exception_handler(vm, UD_VECTOR, NULL);
+ cmd = process_ucall(vcpu);

- if (process_ucall(vcpu) != UCALL_DONE) {
+ if (fep_available) {
+ TEST_ASSERT_EQ(cmd, UCALL_SYNC);
vm_install_exception_handler(vm, GP_VECTOR, guest_fep_gp_handler);

/* Process emulated rdmsr and wrmsr instructions. */
@@ -583,6 +571,7 @@ static void test_msr_filter_allow(void)
/* Confirm the guest completed without issues. */
run_guest_then_process_ucall_done(vcpu);
} else {
+ TEST_ASSERT_EQ(cmd, UCALL_DONE);
printf("To run the instruction emulated tests set the module parameter 'kvm.force_emulation_prefix=1'\n");
}

@@ -804,6 +793,8 @@ static void test_user_exit_msr_flags(void)

int main(int argc, char *argv[])
{
+ fep_available = kvm_is_forced_emulation_enabled();
+
test_msr_filter_allow();

test_msr_filter_deny();
--
2.42.0.869.gea05f2083d-goog