i386: acpi: Add SGX EPC entry to ACPI tables

The ACPI Device entry for SGX EPC is essentially a hack whose primary
purpose is to provide software with a way to autoprobe SGX support,
e.g. to allow software to implement SGX support as a driver.  Details
on the individual EPC sections are not enumerated through ACPI tables,
i.e. software must enumerate the EPC sections via CPUID.  Furthermore,
software expects to see only a single EPC Device in the ACPI tables
regardless of the number of EPC sections in the system.

However, several versions of Windows do rely on the ACPI tables to
enumerate the address and size of the EPC.  So, regardless of the number
of EPC sections exposed to the guest, create exactly *one* EPC device
with a _CRS entry that spans the entirety of all EPC sections (which are
guaranteed to be contiguous in Qemu).

Note, NUMA support for EPC memory is intentionally not considered as
enumerating EPC NUMA information is not yet defined for bare metal.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Yang Zhong <yang.zhong@intel.com>
Message-Id: <20210719112136.57018-20-yang.zhong@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

hw/i386/acpi-build.c

@@ -1841,6 +1841,28 @@ build_dsdt(GArray *table_data, BIOSLinker *linker,
     }
 #endif
 
+    if (pcms->sgx_epc.size != 0) {
+        uint64_t epc_base = pcms->sgx_epc.base;
+        uint64_t epc_size = pcms->sgx_epc.size;
+
+        dev = aml_device("EPC");
+        aml_append(dev, aml_name_decl("_HID", aml_eisaid("INT0E0C")));
+        aml_append(dev, aml_name_decl("_STR",
+                                      aml_unicode("Enclave Page Cache 1.0")));
+        crs = aml_resource_template();
+        aml_append(crs,
+                   aml_qword_memory(AML_POS_DECODE, AML_MIN_FIXED,
+                                    AML_MAX_FIXED, AML_NON_CACHEABLE,
+                                    AML_READ_WRITE, 0, epc_base,
+                                    epc_base + epc_size - 1, 0, epc_size));
+        aml_append(dev, aml_name_decl("_CRS", crs));
+
+        method = aml_method("_STA", 0, AML_NOTSERIALIZED);
+        aml_append(method, aml_return(aml_int(0x0f)));
+        aml_append(dev, method);
+
+        aml_append(sb_scope, dev);
+    }
     aml_append(dsdt, sb_scope);
 
     /* copy AML table into ACPI tables blob and patch header there */