[PATCH V2 11/12] KVM: TDX: Save and restore IA32_DEBUGCTL

[Adrian Hunter <adrian.hunter@intel.com>]

Save the IA32_DEBUGCTL MSR before entering a TDX VCPU and restore it
afterwards.  The TDX Module preserves bits 1, 12, and 14, so if no
other bits are set, no restore is done.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
---
TD vcpu enter/exit v2:
 - New patch
 - Rebased due to moving host_debugctlmsr to struct vcpu_vt.
---
 arch/x86/kvm/vmx/tdx.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index 70996af4be64..0bce00415f42 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -705,6 +705,8 @@ void tdx_prepare_switch_to_guest(struct kvm_vcpu *vcpu)
 	else
 		vt->msr_host_kernel_gs_base = read_msr(MSR_KERNEL_GS_BASE);
 
+	vt->host_debugctlmsr = get_debugctlmsr();
+
 	vt->guest_state_loaded = true;
 }
 
@@ -818,9 +820,14 @@ static noinstr void tdx_vcpu_enter_exit(struct kvm_vcpu *vcpu)
 #define TDX_REGS_UNSUPPORTED_SET	(BIT(VCPU_EXREG_RFLAGS) |	\
 					 BIT(VCPU_EXREG_SEGMENTS))
 
+#define TDX_DEBUGCTL_PRESERVED (DEBUGCTLMSR_BTF | \
+				DEBUGCTLMSR_FREEZE_PERFMON_ON_PMI | \
+				DEBUGCTLMSR_FREEZE_IN_SMM)
+
 fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu, bool force_immediate_exit)
 {
 	struct vcpu_tdx *tdx = to_tdx(vcpu);
+	struct vcpu_vt *vt = to_vt(vcpu);
 
 	/*
 	 * force_immediate_exit requires vCPU entering for events injection with
@@ -846,6 +853,9 @@ fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu, bool force_immediate_exit)
 
 	tdx_vcpu_enter_exit(vcpu);
 
+	if (vt->host_debugctlmsr & ~TDX_DEBUGCTL_PRESERVED)
+		update_debugctlmsr(vt->host_debugctlmsr);
+
 	tdx_user_return_msr_update_cache();
 
 	kvm_load_host_xsave_state(vcpu);
-- 
2.43.0