KVM: SVM: avoid frequency indirect calls

When retpoline is enabled, indirect function calls introduce additional
performance overhead. Avoid frequent indirect calls to VMGEXIT when SEV
is enabled.

Signed-off-by: Peng Hao <flyingpeng@tencent.com>
Link: https://lore.kernel.org/r/20250306075425.66693-1-flyingpeng@tencent.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

Author: flying-122

arch/x86/kvm/svm/svm.c

@@ -3626,6 +3626,10 @@ int svm_invoke_exit_handler(struct kvm_vcpu *vcpu, u64 exit_code)
 		return kvm_emulate_halt(vcpu);
 	else if (exit_code == SVM_EXIT_NPF)
 		return npf_interception(vcpu);
+#ifdef CONFIG_KVM_AMD_SEV
+	else if (exit_code == SVM_EXIT_VMGEXIT)
+		return sev_handle_vmgexit(vcpu);
+#endif
 #endif
 	return svm_exit_handlers[exit_code](vcpu);
 }