KVM: VMX: Extract checking of guest's DEBUGCTL into helper

commit 8a4351ac302cd8c19729ba2636acfd0467c22ae8 upstream.

Move VMX's logic to check DEBUGCTL values into a standalone helper so that
the code can be used by nested VM-Enter to apply the same logic to the
value being loaded from vmcs12.

KVM needs to explicitly check vmcs12->guest_ia32_debugctl on nested
VM-Enter, as hardware may support features that KVM does not, i.e. relying
on hardware to detect invalid guest state will result in false negatives.
Unfortunately, that means applying KVM's funky suppression of BTF and LBR
to vmcs12 so as not to break existing guests.

No functional change intended.

Reviewed-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Link: https://lore.kernel.org/r/20250610232010.162191-6-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Stable-dep-of: 095686e6fcb4 ("KVM: nVMX: Check vmcs12->guest_ia32_debugctl on nested VM-Enter")
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 9ed43bd03c9d5c2aeaee294ce00b456f6db5db6a..43d36c095b9a992b563569681aae346861299419 100644 (file)
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -2199,6 +2199,19 @@ static u64 vmx_get_supported_debugctl(struct kvm_vcpu *vcpu, bool host_initiated
        return debugctl;
 }
 
+static bool vmx_is_valid_debugctl(struct kvm_vcpu *vcpu, u64 data,
+                                 bool host_initiated)
+{
+       u64 invalid;
+
+       invalid = data & ~vmx_get_supported_debugctl(vcpu, host_initiated);
+       if (invalid & (DEBUGCTLMSR_BTF | DEBUGCTLMSR_LBR)) {
+               kvm_pr_unimpl_wrmsr(vcpu, MSR_IA32_DEBUGCTLMSR, data);
+               invalid &= ~(DEBUGCTLMSR_BTF | DEBUGCTLMSR_LBR);
+       }
+       return !invalid;
+}
+
 /*
  * Writes msr value into the appropriate "register".
  * Returns 0 on success, non-0 otherwise.
@@ -2267,19 +2280,12 @@ int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
                }
                vmcs_writel(GUEST_SYSENTER_ESP, data);
                break;
-       case MSR_IA32_DEBUGCTLMSR: {
-               u64 invalid;
-
-               invalid = data & ~vmx_get_supported_debugctl(vcpu, msr_info->host_initiated);
-               if (invalid & (DEBUGCTLMSR_BTF|DEBUGCTLMSR_LBR)) {
-                       kvm_pr_unimpl_wrmsr(vcpu, msr_index, data);
-                       data &= ~(DEBUGCTLMSR_BTF|DEBUGCTLMSR_LBR);
-                       invalid &= ~(DEBUGCTLMSR_BTF|DEBUGCTLMSR_LBR);
-               }
-
-               if (invalid)
+       case MSR_IA32_DEBUGCTLMSR:
+               if (!vmx_is_valid_debugctl(vcpu, data, msr_info->host_initiated))
                        return 1;
 
+               data &= vmx_get_supported_debugctl(vcpu, msr_info->host_initiated);
+
                if (is_guest_mode(vcpu) && get_vmcs12(vcpu)->vm_exit_controls &
                                                VM_EXIT_SAVE_DEBUG_CONTROLS)
                        get_vmcs12(vcpu)->guest_ia32_debugctl = data;
@@ -2289,7 +2295,6 @@ int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
                    (data & DEBUGCTLMSR_LBR))
                        intel_pmu_create_guest_lbr_event(vcpu);
                return 0;
-       }
        case MSR_IA32_BNDCFGS:
                if (!kvm_mpx_supported() ||
                    (!msr_info->host_initiated &&