KVM: SVM: Fix #GP handling for doubly-nested virtualization

Under the case of nested on nested (L0, L1, L2 are all hypervisors),
we do not support emulation of the vVMLOAD/VMSAVE feature, the
L0 hypervisor can inject the proper #VMEXIT to inform L1 of what is
happening and L1 can avoid invoking the #GP workaround.  For this
reason we turns on guest VM's X86_FEATURE_SVME_ADDR_CHK bit for KVM
running inside VM to receive the notification and change behavior.

Similarly we check if vcpu is under guest mode before emulating the
vmware-backdoor instructions. For the case of nested on nested, we
let the guest handle it.
Co-developed-by: Bandan Das <bsd@redhat.com>
Signed-off-by: Bandan Das <bsd@redhat.com>
Signed-off-by: Wei Huang <wei.huang2@amd.com>
Tested-by: Maxim Levitsky <mlevitsk@redhat.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20210126081831.570253-5-wei.huang2@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/svm/svm.c

@@ -933,6 +933,9 @@ static __init void svm_set_cpu_caps(void)
 
 		if (npt_enabled)
 			kvm_cpu_cap_set(X86_FEATURE_NPT);
+
+		/* Nested VM can receive #VMEXIT instead of triggering #GP */
+		kvm_cpu_cap_set(X86_FEATURE_SVME_ADDR_CHK);
 	}
 
 	/* CPUID 0x80000008 */
@@ -2202,6 +2205,11 @@ static int svm_instr_opcode(struct kvm_vcpu *vcpu)
 
 static int emulate_svm_instr(struct kvm_vcpu *vcpu, int opcode)
 {
+	const int guest_mode_exit_codes[] = {
+		[SVM_INSTR_VMRUN] = SVM_EXIT_VMRUN,
+		[SVM_INSTR_VMLOAD] = SVM_EXIT_VMLOAD,
+		[SVM_INSTR_VMSAVE] = SVM_EXIT_VMSAVE,
+	};
 	int (*const svm_instr_handlers[])(struct vcpu_svm *svm) = {
 		[SVM_INSTR_VMRUN] = vmrun_interception,
 		[SVM_INSTR_VMLOAD] = vmload_interception,
@@ -2209,6 +2217,13 @@ static int emulate_svm_instr(struct kvm_vcpu *vcpu, int opcode)
 	};
 	struct vcpu_svm *svm = to_svm(vcpu);
 
+	if (is_guest_mode(vcpu)) {
+		svm->vmcb->control.exit_code = guest_mode_exit_codes[opcode];
+		svm->vmcb->control.exit_info_1 = 0;
+		svm->vmcb->control.exit_info_2 = 0;
+
+		return nested_svm_vmexit(svm);
+	} else
 		return svm_instr_handlers[opcode](svm);
 }
 
@@ -2244,6 +2259,7 @@ static int gp_interception(struct vcpu_svm *svm)
 		 * VMware backdoor emulation on #GP interception only handles
 		 * IN{S}, OUT{S}, and RDPMC.
 		 */
+		if (!is_guest_mode(vcpu))
 			return kvm_emulate_instruction(vcpu,
 				EMULTYPE_VMWARE_GP | EMULTYPE_NO_DECODE);
 	} else