KVM: x86: introduce ISA specific SMM entry/exit callbacks

Entering and exiting SMM may require ISA specific handling under certain
circumstances. This commit adds two new callbacks with empty implementations.
Actual functionality will be added in following commits.

* pre_enter_smm() is to be called when injecting an SMM, before any
  SMM related vcpu state has been changed
* pre_leave_smm() is to be called when emulating the RSM instruction,
  when the vcpu is in real mode and before any SMM related vcpu state
  has been restored
Signed-off-by: NLadi Prosek <lprosek@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

arch/x86/include/asm/kvm_emulate.h

@@ -225,6 +225,8 @@ struct x86_emulate_ops {
 
 	unsigned (*get_hflags)(struct x86_emulate_ctxt *ctxt);
 	void (*set_hflags)(struct x86_emulate_ctxt *ctxt, unsigned hflags);
+	int (*pre_leave_smm)(struct x86_emulate_ctxt *ctxt, u64 smbase);
+
 };
 
 typedef u32 __attribute__((vector_size(16))) sse128_t;

arch/x86/include/asm/kvm_host.h

@@ -1061,6 +1061,9 @@ struct kvm_x86_ops {
 	void (*cancel_hv_timer)(struct kvm_vcpu *vcpu);
 
 	void (*setup_mce)(struct kvm_vcpu *vcpu);
+
+	int (*pre_enter_smm)(struct kvm_vcpu *vcpu, char *smstate);
+	int (*pre_leave_smm)(struct kvm_vcpu *vcpu, u64 smbase);
 };
 
 struct kvm_arch_async_pf {

arch/x86/kvm/emulate.c

@@ -2591,6 +2591,15 @@ static int em_rsm(struct x86_emulate_ctxt *ctxt)
 	ctxt->ops->set_msr(ctxt, MSR_EFER, efer);
 
 	smbase = ctxt->ops->get_smbase(ctxt);
+
+	/*
+	 * Give pre_leave_smm() a chance to make ISA-specific changes to the
+	 * vCPU state (e.g. enter guest mode) before loading state from the SMM
+	 * state-save area.
+	 */
+	if (ctxt->ops->pre_leave_smm(ctxt, smbase))
+		return X86EMUL_UNHANDLEABLE;
+
 	if (emulator_has_longmode(ctxt))
 		ret = rsm_load_state_64(ctxt, smbase + 0x8000);
 	else

arch/x86/kvm/svm.c

@@ -5401,6 +5401,18 @@ static void svm_setup_mce(struct kvm_vcpu *vcpu)
 	vcpu->arch.mcg_cap &= 0x1ff;
 }
 
+static int svm_pre_enter_smm(struct kvm_vcpu *vcpu, char *smstate)
+{
+	/* TODO: Implement */
+	return 0;
+}
+
+static int svm_pre_leave_smm(struct kvm_vcpu *vcpu, u64 smbase)
+{
+	/* TODO: Implement */
+	return 0;
+}
+
 static struct kvm_x86_ops svm_x86_ops __ro_after_init = {
 	.cpu_has_kvm_support = has_svm,
 	.disabled_by_bios = is_disabled,
@@ -5511,6 +5523,9 @@ static struct kvm_x86_ops svm_x86_ops __ro_after_init = {
 	.deliver_posted_interrupt = svm_deliver_avic_intr,
 	.update_pi_irte = svm_update_pi_irte,
 	.setup_mce = svm_setup_mce,
+
+	.pre_enter_smm = svm_pre_enter_smm,
+	.pre_leave_smm = svm_pre_leave_smm,
 };
 
 static int __init svm_init(void)

arch/x86/kvm/vmx.c

@@ -11916,6 +11916,18 @@ static void vmx_setup_mce(struct kvm_vcpu *vcpu)
 			~FEATURE_CONTROL_LMCE;
 }
 
+static int vmx_pre_enter_smm(struct kvm_vcpu *vcpu, char *smstate)
+{
+	/* TODO: Implement */
+	return 0;
+}
+
+static int vmx_pre_leave_smm(struct kvm_vcpu *vcpu, u64 smbase)
+{
+	/* TODO: Implement */
+	return 0;
+}
+
 static struct kvm_x86_ops vmx_x86_ops __ro_after_init = {
 	.cpu_has_kvm_support = cpu_has_kvm_support,
 	.disabled_by_bios = vmx_disabled_by_bios,
@@ -12041,6 +12053,9 @@ static struct kvm_x86_ops vmx_x86_ops __ro_after_init = {
 #endif
 
 	.setup_mce = vmx_setup_mce,
+
+	.pre_enter_smm = vmx_pre_enter_smm,
+	.pre_leave_smm = vmx_pre_leave_smm,
 };
 
 static int __init vmx_init(void)

arch/x86/kvm/x86.c

@@ -5281,6 +5281,11 @@ static void emulator_set_hflags(struct x86_emulate_ctxt *ctxt, unsigned emul_fla
 	kvm_set_hflags(emul_to_vcpu(ctxt), emul_flags);
 }
 
+static int emulator_pre_leave_smm(struct x86_emulate_ctxt *ctxt, u64 smbase)
+{
+	return kvm_x86_ops->pre_leave_smm(emul_to_vcpu(ctxt), smbase);
+}
+
 static const struct x86_emulate_ops emulate_ops = {
 	.read_gpr            = emulator_read_gpr,
 	.write_gpr           = emulator_write_gpr,
@@ -5322,6 +5327,7 @@ static const struct x86_emulate_ops emulate_ops = {
 	.set_nmi_mask        = emulator_set_nmi_mask,
 	.get_hflags          = emulator_get_hflags,
 	.set_hflags          = emulator_set_hflags,
+	.pre_leave_smm       = emulator_pre_leave_smm,
 };
 
 static void toggle_interruptibility(struct kvm_vcpu *vcpu, u32 mask)
@@ -6647,13 +6653,20 @@ static void enter_smm(struct kvm_vcpu *vcpu)
 	u32 cr0;
 
 	trace_kvm_enter_smm(vcpu->vcpu_id, vcpu->arch.smbase, true);
-	vcpu->arch.hflags |= HF_SMM_MASK;
 	memset(buf, 0, 512);
 	if (guest_cpuid_has(vcpu, X86_FEATURE_LM))
 		enter_smm_save_state_64(vcpu, buf);
 	else
 		enter_smm_save_state_32(vcpu, buf);
 
+	/*
+	 * Give pre_enter_smm() a chance to make ISA-specific changes to the
+	 * vCPU state (e.g. leave guest mode) after we've saved the state into
+	 * the SMM state-save area.
+	 */
+	kvm_x86_ops->pre_enter_smm(vcpu, buf);
+
+	vcpu->arch.hflags |= HF_SMM_MASK;
 	kvm_vcpu_write_guest(vcpu, vcpu->arch.smbase + 0xfe00, buf, sizeof(buf));
 
 	if (kvm_x86_ops->get_nmi_mask(vcpu))