KVM: nSVM: fix SMI injection in guest mode

Entering SMM while running in guest mode wasn't working very well because several
pieces of the vcpu state were left set up for nested operation.

Some of the issues observed:

* L1 was getting unexpected VM exits (using L1 interception controls but running
  in SMM execution environment)
* MMU was confused (walk_mmu was still set to nested_mmu)
* INTERCEPT_SMI was not emulated for L1 (KVM never injected SVM_EXIT_SMI)

Intel SDM actually prescribes the logical processor to "leave VMX operation" upon
entering SMM in 34.14.1 Default Treatment of SMI Delivery. AMD doesn't seem to
document this but they provide fields in the SMM state-save area to stash the
current state of SVM. What we need to do is basically get out of guest mode for
the duration of SMM. All this completely transparent to L1, i.e. L1 is not given
control and no L1 observable state changes.

To avoid code duplication this commit takes advantage of the existing nested
vmexit and run functionality, perhaps at the cost of efficiency. To get out of
guest mode, nested_svm_vmexit is called, unchanged. Re-entering is performed using
enter_svm_guest_mode.

This commit fixes running Windows Server 2016 with Hyper-V enabled in a VM with
OVMF firmware (OVMF_CODE-need-smm.fd).
Signed-off-by: NLadi Prosek <lprosek@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

arch/x86/include/asm/kvm_host.h

@@ -1430,4 +1430,7 @@ static inline int kvm_cpu_get_apicid(int mps_cpu)
 #endif
 }
 
+#define put_smstate(type, buf, offset, val)                      \
+	*(type *)((buf) + (offset) - 0x7e00) = val
+
 #endif /* _ASM_X86_KVM_HOST_H */

arch/x86/kvm/svm.c

@@ -5409,19 +5409,71 @@ static void svm_setup_mce(struct kvm_vcpu *vcpu)
 
 static int svm_smi_allowed(struct kvm_vcpu *vcpu)
 {
+	struct vcpu_svm *svm = to_svm(vcpu);
+
+	/* Per APM Vol.2 15.22.2 "Response to SMI" */
+	if (!gif_set(svm))
+		return 0;
+
+	if (is_guest_mode(&svm->vcpu) &&
+	    svm->nested.intercept & (1ULL << INTERCEPT_SMI)) {
+		/* TODO: Might need to set exit_info_1 and exit_info_2 here */
+		svm->vmcb->control.exit_code = SVM_EXIT_SMI;
+		svm->nested.exit_required = true;
+		return 0;
+	}
+
 	return 1;
 }
 
 static int svm_pre_enter_smm(struct kvm_vcpu *vcpu, char *smstate)
 {
-	/* TODO: Implement */
+	struct vcpu_svm *svm = to_svm(vcpu);
+	int ret;
+
+	if (is_guest_mode(vcpu)) {
+		/* FED8h - SVM Guest */
+		put_smstate(u64, smstate, 0x7ed8, 1);
+		/* FEE0h - SVM Guest VMCB Physical Address */
+		put_smstate(u64, smstate, 0x7ee0, svm->nested.vmcb);
+
+		svm->vmcb->save.rax = vcpu->arch.regs[VCPU_REGS_RAX];
+		svm->vmcb->save.rsp = vcpu->arch.regs[VCPU_REGS_RSP];
+		svm->vmcb->save.rip = vcpu->arch.regs[VCPU_REGS_RIP];
+
+		ret = nested_svm_vmexit(svm);
+		if (ret)
+			return ret;
+	}
 	return 0;
 }
 
 static int svm_pre_leave_smm(struct kvm_vcpu *vcpu, u64 smbase)
 {
-	/* TODO: Implement */
-	return 0;
+	struct vcpu_svm *svm = to_svm(vcpu);
+	struct vmcb *nested_vmcb;
+	struct page *page;
+	struct {
+		u64 guest;
+		u64 vmcb;
+	} svm_state_save;
+	int ret;
+
+	ret = kvm_vcpu_read_guest(vcpu, smbase + 0xfed8, &svm_state_save,
+				  sizeof(svm_state_save));
+	if (ret)
+		return ret;
+
+	if (svm_state_save.guest) {
+		vcpu->arch.hflags &= ~HF_SMM_MASK;
+		nested_vmcb = nested_svm_map(svm, svm_state_save.vmcb, &page);
+		if (nested_vmcb)
+			enter_svm_guest_mode(svm, svm_state_save.vmcb, nested_vmcb, page);
+		else
+			ret = 1;
+		vcpu->arch.hflags |= HF_SMM_MASK;
+	}
+	return ret;
 }
 
 static struct kvm_x86_ops svm_x86_ops __ro_after_init = {

arch/x86/kvm/x86.c

@@ -6485,9 +6485,6 @@ static void process_nmi(struct kvm_vcpu *vcpu)
 	kvm_make_request(KVM_REQ_EVENT, vcpu);
 }
 
-#define put_smstate(type, buf, offset, val)			  \
-	*(type *)((buf) + (offset) - 0x7e00) = val
-
 static u32 enter_smm_get_segment_flags(struct kvm_segment *seg)
 {
 	u32 flags = 0;