Re: [PATCH v16 50/51] KVM: selftests: Verify MSRs are (not) in save/restore list when (un)supported

Chao Gao
2025-09-23T06:46:47Z

On Fri, Sep 19, 2025 at 03:32:57PM -0700, Sean Christopherson wrote:
>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.

is this paragraph related to this patch? the tracking is done in a previous
patch instead of this patch. So maybe just drop this paragraph.

>
>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 7c6d846e42dd..91dc66bfdac2 100644
>--- a/tools/testing/selftests/kvm/x86/msrs_test.c
>+++ b/tools/testing/selftests/kvm/x86/msrs_test.c
>@@ -437,12 +437,32 @@ 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

I am not sure why LM is mentioned here. Is it a leftover from one of your
previous attempts?

>+ * 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,

^ an "in" is missing here.

The code change looks good. So,

Reviewed-by: Chao Gao <chao.gao@intel.com>

>+ 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);
>--
>2.51.0.470.ga7dc726c21-goog
>