linux-kernel - [PATCH 7/9] KVM: x86: Remove ordering check b/w MSR_PLATFORM_INFO and MISC_FEATURES

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Message-ID: <20240802185511.305849-8-seanjc@google.com>
Date: Fri,  2 Aug 2024 11:55:09 -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 7/9] KVM: x86: Remove ordering check b/w MSR_PLATFORM_INFO and MISC_FEATURES_ENABLES

Drop KVM's odd restriction that disallows clearing CPUID_FAULT in
MSR_PLATFORM_INFO if CPL>0 CPUID faulting is enabled in
MSR_MISC_FEATURES_ENABLES.  KVM generally doesn't require specific
ordering when userspace sets MSRs, and the completely arbitrary order of
MSRs in emulated_msrs_all means that a userspace that uses KVM's list
verbatim could run afoul of the check.

Dropping the restriction obviously means that userspace could stuff a
nonsensical vCPU model, but that's the case all over KVM.  KVM typically
restricts userspace MSR writes only when it makes things easier for KVM
and/or userspace.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/x86.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 8bce40c649b4..32483cc16d6a 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4119,9 +4119,7 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		vcpu->arch.osvw.status = data;
 		break;
 	case MSR_PLATFORM_INFO:
-		if (!msr_info->host_initiated ||
-		    (!(data & MSR_PLATFORM_INFO_CPUID_FAULT) &&
-		     cpuid_fault_enabled(vcpu)))
+		if (!msr_info->host_initiated)
 			return 1;
 		vcpu->arch.msr_platform_info = data;
 		break;
-- 
2.46.0.rc2.264.g509ed76dc8-goog