KVM: x86: Fully re-initialize supported_mce_cap on vendor module load

Effectively reset supported_mce_cap on vendor module load to ensure that
capabilities aren't unintentionally preserved across module reload, e.g.
if kvm-intel.ko added a module param to control LMCE support, or if
someone somehow managed to load a vendor module that doesn't support LMCE
after loading and unloading kvm-intel.ko.

Practically speaking, this bug is a non-issue as kvm-intel.ko doesn't have
a module param for LMCE, and there is no system in the world that supports
both kvm-intel.ko and kvm-amd.ko.

Fixes: c45dcc71 ("KVM: VMX: enable guest access to LMCE related MSRs")
Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Message-ID: <20240423165328.2853870-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/x86.c

@@ -92,9 +92,7 @@
 #define MAX_IO_MSRS 256
 #define KVM_MAX_MCE_BANKS 32
 
-struct kvm_caps kvm_caps __read_mostly = {
-	.supported_mce_cap = MCG_CTL_P | MCG_SER_P,
-};
+struct kvm_caps kvm_caps __read_mostly;
 EXPORT_SYMBOL_GPL(kvm_caps);
 
 #define  ERR_PTR_USR(e)  ((void __user *)ERR_PTR(e))
@@ -9776,6 +9774,7 @@ int kvm_x86_vendor_init(struct kvm_x86_init_ops *ops)
 		goto out_free_percpu;
 
 	kvm_caps.supported_vm_types = BIT(KVM_X86_DEFAULT_VM);
+	kvm_caps.supported_mce_cap = MCG_CTL_P | MCG_SER_P;
 
 	if (boot_cpu_has(X86_FEATURE_XSAVE)) {
 		host_xcr0 = xgetbv(XCR_XFEATURE_ENABLED_MASK);