KVM: x86: Do compatibility checks when onlining CPU

Do compatibility checks when enabling hardware to effectively add
compatibility checks when onlining a CPU.  Abort enabling, i.e. the
online process, if the (hotplugged) CPU is incompatible with the known
good setup.

At init time, KVM does compatibility checks to ensure that all online
CPUs support hardware virtualization and a common set of features. But
KVM uses hotplugged CPUs without such compatibility checks. On Intel
CPUs, this leads to #GP if the hotplugged CPU doesn't support VMX, or
VM-Entry failure if the hotplugged CPU doesn't support all features
enabled by KVM.

Note, this is little more than a NOP on SVM, as SVM already checks for
full SVM support during hardware enabling.

Opportunistically add a pr_err() if setup_vmcs_config() fails, and
tweak all error messages to output which CPU failed.

Signed-off-by: Chao Gao <chao.gao@intel.com>
Co-developed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Acked-by: Kai Huang <kai.huang@intel.com>
Message-Id: <20221130230934.1014142-41-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 10 insertions, 5 deletions

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 3d5e93ceed6b..73005d7e4e43 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -2747,14 +2747,16 @@ static int setup_vmcs_config(struct vmcs_config *vmcs_conf,
 
 static bool kvm_is_vmx_supported(void)
 {
+	int cpu = raw_smp_processor_id();
+
 	if (!cpu_has_vmx()) {
-		pr_err("CPU doesn't support VMX\n");
+		pr_err("VMX not supported by CPU %d\n", cpu);
 		return false;
 	}
 
 	if (!this_cpu_has(X86_FEATURE_MSR_IA32_FEAT_CTL) ||
 	    !this_cpu_has(X86_FEATURE_VMX)) {
-		pr_err("VMX not enabled (by BIOS) in MSR_IA32_FEAT_CTL\n");
+		pr_err("VMX not enabled (by BIOS) in MSR_IA32_FEAT_CTL on CPU %d\n", cpu);
 		return false;
 	}
 
@@ -2763,18 +2765,21 @@ static bool kvm_is_vmx_supported(void)
 
 static int vmx_check_processor_compat(void)
 {
+	int cpu = raw_smp_processor_id();
 	struct vmcs_config vmcs_conf;
 	struct vmx_capability vmx_cap;
 
 	if (!kvm_is_vmx_supported())
 		return -EIO;
 
-	if (setup_vmcs_config(&vmcs_conf, &vmx_cap) < 0)
+	if (setup_vmcs_config(&vmcs_conf, &vmx_cap) < 0) {
+		pr_err("Failed to setup VMCS config on CPU %d\n", cpu);
 		return -EIO;
+	}
 	if (nested)
 		nested_vmx_setup_ctls_msrs(&vmcs_conf, vmx_cap.ept);
-	if (memcmp(&vmcs_config, &vmcs_conf, sizeof(struct vmcs_config)) != 0) {
-		pr_err("CPU %d feature inconsistency!\n", smp_processor_id());
+	if (memcmp(&vmcs_config, &vmcs_conf, sizeof(struct vmcs_config))) {
+		pr_err("Inconsistent VMCS config on CPU %d\n", cpu);
 		return -EIO;
 	}
 	return 0;