linux-kernel - [PATCH 2/9] KVM: x86: Disallow changing MSR_PLATFORM

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Message-ID: <20240802185511.305849-3-seanjc@google.com>
Date: Fri,  2 Aug 2024 11:55:04 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Paolo Bonzini <pbonzini@...hat.com>, Sean Christopherson <seanjc@...gle.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 2/9] KVM: x86: Disallow changing MSR_PLATFORM_INFO after vCPU
 has run

Tag MSR_PLATFORM_INFO as a feature MSR (because it is), i.e. disallow it
from being modified after the vCPU has run.

To make KVM's selftest compliant, simply delete the userspace MSR write
that restores KVM's original value at the end of the test.  Verifying that
userspace can write back what it originally read is uninteresting in this
particular case, because KVM doesn't enforce _any_ bits in the MSR, i.e.
userspace should be able to write any arbitrary value.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/x86.c                                      | 1 +
 tools/testing/selftests/kvm/x86_64/platform_info_test.c | 2 --
 2 files changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 9d667c5ab1a9..a9566c035857 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -451,6 +451,7 @@ static const u32 msr_based_features_all_except_vmx[] = {
 	MSR_IA32_UCODE_REV,
 	MSR_IA32_ARCH_CAPABILITIES,
 	MSR_IA32_PERF_CAPABILITIES,
+	MSR_PLATFORM_INFO,
 };
 
 static u32 msr_based_features[ARRAY_SIZE(msr_based_features_all_except_vmx) +
diff --git a/tools/testing/selftests/kvm/x86_64/platform_info_test.c b/tools/testing/selftests/kvm/x86_64/platform_info_test.c
index eda88080c186..9cbf283ebc55 100644
--- a/tools/testing/selftests/kvm/x86_64/platform_info_test.c
+++ b/tools/testing/selftests/kvm/x86_64/platform_info_test.c
@@ -72,8 +72,6 @@ int main(int argc, char *argv[])
 	}
 
 done:
-	vcpu_set_msr(vcpu, MSR_PLATFORM_INFO, msr_platform_info);
-
 	kvm_vm_free(vm);
 
 	return 0;
-- 
2.46.0.rc2.264.g509ed76dc8-goog