kvm: Allow the Hyper-V vendor ID to be specified

According to Microsoft documentation, the signature in the standard
hypervisor CPUID leaf at 0x40000000 identifies the Vendor ID and is
for reporting and diagnostic purposes only.  We can therefore allow
the user to change it to whatever they want, within the 12 character
limit.  Add a new hv-vendor-id option to the -cpu flag to allow
for this, ex:

 -cpu host,hv_time,hv-vendor-id=KeenlyKVM

Link: http://msdn.microsoft.com/library/windows/hardware/hh975392
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Message-Id: <20151016153356.28104.48612.stgit@gimli.home>
[Adjust error message to match the property name, use error_report. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

target-i386/cpu-qom.h

diff --git a/target-i386/cpu-qom.h b/target-i386/cpu-qom.h
index 9eab41b..e3bfe9d 100644
--- a/target-i386/cpu-qom.h
+++ b/target-i386/cpu-qom.h
@@ -88,6 +88,7 @@
     bool hyperv_vapic;
     bool hyperv_relaxed_timing;
     int hyperv_spinlock_attempts;
+    char *hyperv_vendor_id;
     bool hyperv_time;
     bool hyperv_crash;
     bool hyperv_reset;

target-i386/cpu.c

diff --git a/target-i386/cpu.c b/target-i386/cpu.c
index d2b0619..5f53af2 100644
--- a/target-i386/cpu.c
+++ b/target-i386/cpu.c
@@ -3149,6 +3149,7 @@
     DEFINE_PROP_UINT32("level", X86CPU, env.cpuid_level, 0),
     DEFINE_PROP_UINT32("xlevel", X86CPU, env.cpuid_xlevel, 0),
     DEFINE_PROP_UINT32("xlevel2", X86CPU, env.cpuid_xlevel2, 0),
+    DEFINE_PROP_STRING("hv-vendor-id", X86CPU, hyperv_vendor_id),
     DEFINE_PROP_END_OF_LIST()
 };
 

target-i386/kvm.c

diff --git a/target-i386/kvm.c b/target-i386/kvm.c
index 010ac51..64046cb 100644
--- a/target-i386/kvm.c
+++ b/target-i386/kvm.c
@@ -28,6 +28,7 @@
 #include "exec/gdbstub.h"
 #include "qemu/host-utils.h"
 #include "qemu/config-file.h"
+#include "qemu/error-report.h"
 #include "hw/i386/pc.h"
 #include "hw/i386/apic.h"
 #include "hw/i386/apic_internal.h"
@@ -505,7 +506,18 @@
     if (hyperv_enabled(cpu)) {
         c = &cpuid_data.entries[cpuid_i++];
         c->function = HYPERV_CPUID_VENDOR_AND_MAX_FUNCTIONS;
-        memcpy(signature, "Microsoft Hv", 12);
+        if (!cpu->hyperv_vendor_id) {
+            memcpy(signature, "Microsoft Hv", 12);
+        } else {
+            size_t len = strlen(cpu->hyperv_vendor_id);
+
+            if (len > 12) {
+                error_report("hv-vendor-id truncated to 12 characters");
+                len = 12;
+            }
+            memset(signature, 0, 12);
+            memcpy(signature, cpu->hyperv_vendor_id, len);
+        }
         c->eax = HYPERV_CPUID_MIN;
         c->ebx = signature[0];
         c->ecx = signature[1];