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

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Message-ID: <aNJCNMGLIIVlyC/p@intel.com>
Date: Tue, 23 Sep 2025 14:46:12 +0800
From: Chao Gao <chao.gao@...el.com>
To: Sean Christopherson <seanjc@...gle.com>
CC: Paolo Bonzini <pbonzini@...hat.com>, <kvm@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, Tom Lendacky <thomas.lendacky@....com>,
	Mathias Krause <minipli@...ecurity.net>, John Allen <john.allen@....com>,
	Rick Edgecombe <rick.p.edgecombe@...el.com>, Binbin Wu
	<binbin.wu@...ux.intel.com>, Xiaoyao Li <xiaoyao.li@...el.com>, "Maxim
 Levitsky" <mlevitsk@...hat.com>, Zhang Yi Z <yi.z.zhang@...ux.intel.com>,
	"Xin Li" <xin@...or.com>
Subject: Re: [PATCH v16 50/51] KVM: selftests: Verify MSRs are (not) in
 save/restore list when (un)supported

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@...gle.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@...el.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
>