i386: Propagate SGX CPUID sub-leafs to KVM

The SGX sub-leafs are enumerated at CPUID 0x12.  Indices 0 and 1 are
always present when SGX is supported, and enumerate SGX features and
capabilities.  Indices >=2 are directly correlated with the platform's
EPC sections.  Because the number of EPC sections is dynamic and user
defined, the number of SGX sub-leafs is "NULL" terminated.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Yang Zhong <yang.zhong@intel.com>
Message-Id: <20210719112136.57018-15-yang.zhong@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

target/i386/kvm/kvm.c

@@ -1703,6 +1703,25 @@ int kvm_arch_init_vcpu(CPUState *cs)
             }
             break;
         case 0x7:
+        case 0x12:
+            for (j = 0; ; j++) {
+                c->function = i;
+                c->flags = KVM_CPUID_FLAG_SIGNIFCANT_INDEX;
+                c->index = j;
+                cpu_x86_cpuid(env, i, j, &c->eax, &c->ebx, &c->ecx, &c->edx);
+
+                if (j > 1 && (c->eax & 0xf) != 1) {
+                    break;
+                }
+
+                if (cpuid_i == KVM_MAX_CPUID_ENTRIES) {
+                    fprintf(stderr, "cpuid_data is full, no space for "
+                                "cpuid(eax:0x12,ecx:0x%x)\n", j);
+                    abort();
+                }
+                c = &cpuid_data.entries[cpuid_i++];
+            }
+            break;
         case 0x14: {
             uint32_t times;