cpu/i386: populate CPUID 0x8000_001F when SEV is active

When SEV is enabled, CPUID 0x8000_001F should provide additional
information regarding the feature (such as which page table bit is used
to mark the pages as encrypted etc).

The details for memory encryption CPUID is available in AMD APM
(https://support.amd.com/TechDocs/24594.pdf) Section E.4.17

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Eduardo Habkost <ehabkost@redhat.com>
Reviewed-by: NEduardo Habkost <ehabkost@redhat.com>
Signed-off-by: NBrijesh Singh <brijesh.singh@amd.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

target/i386/cpu.c

@@ -26,6 +26,7 @@
 #include "sysemu/hvf.h"
 #include "sysemu/cpus.h"
 #include "kvm_i386.h"
+#include "sev_i386.h"
 
 #include "qemu/error-report.h"
 #include "qemu/option.h"
@@ -3612,6 +3613,13 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count,
         *ecx = 0;
         *edx = 0;
         break;
+    case 0x8000001F:
+        *eax = sev_enabled() ? 0x2 : 0;
+        *ebx = sev_get_cbit_position();
+        *ebx |= sev_get_reduced_phys_bits() << 6;
+        *ecx = 0;
+        *edx = 0;
+        break;
     default:
         /* reserved values: zero */
         *eax = 0;
@@ -4042,6 +4050,11 @@ static void x86_cpu_expand_features(X86CPU *cpu, Error **errp)
         if (env->features[FEAT_8000_0001_ECX] & CPUID_EXT3_SVM) {
             x86_cpu_adjust_level(cpu, &env->cpuid_min_xlevel, 0x8000000A);
         }
+
+        /* SEV requires CPUID[0x8000001F] */
+        if (sev_enabled()) {
+            x86_cpu_adjust_level(cpu, &env->cpuid_min_xlevel, 0x8000001F);
+        }
     }
 
     /* Set cpuid_*level* based on cpuid_min_*level, if not explicitly set */