*vcpu)
-{
-	struct vcpu_vt *vt = to_vt(vcpu);
-
-	if (vt->guest_state_loaded)
-		return;
-
-	if (likely(is_64bit_mm(current->mm)))
-		vt->msr_host_kernel_gs_base = current->thread.gsbase;
-	else
-		vt->msr_host_kernel_gs_base = read_msr(MSR_KERNEL_GS_BASE);
-
-	vt->guest_state_loaded = true;
-}
-
 struct tdx_uret_msr {
 	u32 msr;
 	unsigned int slot;
@@ -795,19 +776,38 @@ static struct tdx_uret_msr tdx_uret_msrs
 	{.msr = MSR_TSC_AUX,},
 };
 
-static void tdx_user_return_msr_update_cache(void)
+void tdx_prepare_switch_to_guest(struct kvm_vcpu *vcpu)
 {
+	struct vcpu_vt *vt = to_vt(vcpu);
 	int i;
 
+	if (vt->guest_state_loaded)
+		return;
+
+	if (likely(is_64bit_mm(current->mm)))
+		vt->msr_host_kernel_gs_base = current->thread.gsbase;
+	else
+		vt->msr_host_kernel_gs_base = read_msr(MSR_KERNEL_GS_BASE);
+
+	vt->guest_state_loaded = true;
+
+	/*
+	 * Explicitly set user-return MSRs that are clobbered by the TDX-Module
+	 * if VP.ENTER succeeds, i.e. on TD-Exit, with the values that would be
+	 * written by the TDX-Module.  Don't rely on the TDX-Module to actually
+	 * clobber the MSRs, as the contract is poorly defined and not upheld.
+	 * E.g. the TDX-Module will synthesize an EPT Violation without doing
+	 * VM-Enter if it suspects a zero-step attack, and never "restore" VMM
+	 * state.
+	 */
 	for (i = 0; i < ARRAY_SIZE(tdx_uret_msrs); i++)
-		kvm_user_return_msr_update_cache(tdx_uret_msrs[i].slot,
-						 tdx_uret_msrs[i].defval);
+		kvm_set_user_return_msr(tdx_uret_msrs[i].slot,
+					tdx_uret_msrs[i].defval, -1ull);
 }
 
 static void tdx_prepare_switch_to_host(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_vt *vt = to_vt(vcpu);
-	struct vcpu_tdx *tdx = to_tdx(vcpu);
 
 	if (!vt->guest_state_loaded)
 		return;
@@ -815,11 +815,6 @@ static void tdx_prepare_switch_to_host(s
 	++vcpu->stat.host_state_reload;
 	wrmsrl(MSR_KERNEL_GS_BASE, vt->msr_host_kernel_gs_base);
 
-	if (tdx->guest_entered) {
-		tdx_user_return_msr_update_cache();
-		tdx->guest_entered = false;
-	}
-
 	vt->guest_state_loaded = false;
 }
 
@@ -1059,7 +1054,6 @@ fastpath_t tdx_vcpu_run(struct kvm_vcpu
 		update_debugctlmsr(vcpu->arch.host_debugctl);
 
 	tdx_load_host_xsave_state(vcpu);
-	tdx->guest_entered = true;
 
 	vcpu->arch.regs_avail &= TDX_REGS_AVAIL_SET;
 
@@ -3447,10 +3441,6 @@ static int __init __tdx_bringup(void)
 		/*
 		 * Check if MSRs (tdx_uret_msrs) can be saved/restored
 		 * before returning to user space.
-		 *
-		 * this_cpu_ptr(user_return_msrs)->registered isn't checked
-		 * because the registration is done at vcpu runtime by
-		 * tdx_user_return_msr_update_cache().
 		 */
 		tdx_uret_msrs[i].slot = kvm_find_user_return_msr(tdx_uret_msrs[i].msr);
 		if (tdx_uret_msrs[i].slot == -1) {
--- a/arch/x86/kvm/vmx/tdx.h
+++ b/arch/x86/kvm/vmx/tdx.h
@@ -67,7 +67,6 @@ struct vcpu_tdx {
 	u64 vp_enter_ret;
 
 	enum vcpu_tdx_state state;
-	bool guest_entered;
 
 	u64 map_gpa_next;
 	u64 map_gpa_end;
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -681,15 +681,6 @@ int kvm_set_user_return_msr(unsigned slo
 }
 EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_set_user_return_msr);
 
-void kvm_user_return_msr_update_cache(unsigned int slot, u64 value)
-{
-	struct kvm_user_return_msrs *msrs = this_cpu_ptr(user_return_msrs);
-
-	msrs->values[slot].curr = value;
-	kvm_user_return_register_notifier(msrs);
-}
-EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_user_return_msr_update_cache);
-
 u64 kvm_get_user_return_msr(unsigned int slot)
 {
 	return this_cpu_ptr(user_return_msrs)->values[slot].curr;[PATCH 6.18 348/430] KVM: TDX: Explicitly set user-return MSRs that *may* be clobbered by the TDX-ModuleGreg Kroah-Hartman <gregkh@linuxfoundation.org> undefinedstable@vger.kernel.org undefined undefined undefined undefined undefined undefined‹F„Ži