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.

Link: https://lore.kernel.org/r/20240802185511.305849-8-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 7e59d3a0801a2d4dab8f735367fd2dc8abace63f..366fd89d08944ad7039d7bfb8769a5a786ef1051 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4116,9 +4116,7 @@ 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;