[PATCH v15 40/41] KVM: selftests: Verify MSRs are (not) in save/restore list when (un)supported

Sean Christopherson
2025-09-12T23:24:36Z

Add a check in the MSRs test to verify that KVM's reported support for
MSRs with feature bits is consistent between KVM's MSR save/restore lists
and KVM's supported CPUID.

To deal with Intel's wonderful decision to bundle IBT and SHSTK under CET,
track the "second" feature to avoid false failures when running on a CPU
with only one of IBT or SHSTK.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
tools/testing/selftests/kvm/x86/msrs_test.c | 22 ++++++++++++++++++++-
1 file changed, 21 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/kvm/x86/msrs_test.c b/tools/testing/selftests/kvm/x86/msrs_test.c
index 6a956cfe0c65..442409e40da0 100644
--- a/tools/testing/selftests/kvm/x86/msrs_test.c
+++ b/tools/testing/selftests/kvm/x86/msrs_test.c
@@ -392,12 +392,32 @@ static void test_msrs(void)
}

for (idx = 0; idx < ARRAY_SIZE(__msrs); idx++) {
- if (msrs[idx].is_kvm_defined) {
+ struct kvm_msr *msr = &msrs[idx];
+
+ if (msr->is_kvm_defined) {
for (i = 0; i < NR_VCPUS; i++)
host_test_kvm_reg(vcpus[i]);
continue;
}

+ /*
+ * Verify KVM_GET_SUPPORTED_CPUID and KVM_GET_MSR_INDEX_LIST
+ * are consistent with respect to MSRs whose existence is
+ * enumerated via CPUID. Note, using LM as a dummy feature
+ * is a-ok here as well, as all MSRs that abuse LM should be
+ * unconditionally reported in the save/restore list (and
+ * selftests are 64-bit only). Note #2, skip the check for
+ * FS/GS.base MSRs, as they aren't reported in the save/restore
+ * list since their state is managed via SREGS.
+ */
+ TEST_ASSERT(msr->index == MSR_FS_BASE || msr->index == MSR_GS_BASE ||
+ kvm_msr_is_in_save_restore_list(msr->index) ==
+ (kvm_cpu_has(msr->feature) || kvm_cpu_has(msr->feature2)),
+ "%s %s save/restore list, but %s according to CPUID", msr->name,
+ kvm_msr_is_in_save_restore_list(msr->index) ? "is" : "isn't",
+ (kvm_cpu_has(msr->feature) || kvm_cpu_has(msr->feature2)) ?
+ "supported" : "unsupported");
+
sync_global_to_guest(vm, idx);

vcpus_run(vcpus, NR_VCPUS);
--
2.51.0.384.g4c02a37b29-goog