s390: Recognize confidential-guest-support option

At least some s390 cpu models support "Protected Virtualization" (PV),
a mechanism to protect guests from eavesdropping by a compromised
hypervisor.

This is similar in function to other mechanisms like AMD's SEV and
POWER's PEF, which are controlled by the "confidential-guest-support"
machine option.  s390 is a slightly special case, because we already
supported PV, simply by using a CPU model with the required feature
(S390_FEAT_UNPACK).

To integrate this with the option used by other platforms, we
implement the following compromise:

 - When the confidential-guest-support option is set, s390 will
   recognize it, verify that the CPU can support PV (failing if not)
   and set virtio default options necessary for encrypted or protected
   guests, as on other platforms.  i.e. if confidential-guest-support
   is set, we will either create a guest capable of entering PV mode,
   or fail outright.

 - If confidential-guest-support is not set, guests might still be
   able to enter PV mode, if the CPU has the right model.  This may be
   a little surprising, but shouldn't actually be harmful.

To start a guest supporting Protected Virtualization using the new
option use the command line arguments:
    -object s390-pv-guest,id=pv0 -machine confidential-guest-support=pv0

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Tested-by: Christian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>

1 files changed, 17 insertions, 0 deletions

diff --git a/include/hw/s390x/pv.h b/include/hw/s390x/pv.h
index aee758bc2d..1f1f545bfc 100644
--- a/include/hw/s390x/pv.h
+++ b/include/hw/s390x/pv.h
@@ -12,6 +12,9 @@
 #ifndef HW_S390_PV_H
 #define HW_S390_PV_H
 
+#include "qapi/error.h"
+#include "sysemu/kvm.h"
+
 #ifdef CONFIG_KVM
 #include "cpu.h"
 #include "hw/s390x/s390-virtio-ccw.h"
@@ -55,4 +58,18 @@ static inline void s390_pv_unshare(void) {}
 static inline void s390_pv_inject_reset_error(CPUState *cs) {};
 #endif /* CONFIG_KVM */
 
+int s390_pv_kvm_init(ConfidentialGuestSupport *cgs, Error **errp);
+static inline int s390_pv_init(ConfidentialGuestSupport *cgs, Error **errp)
+{
+    if (!cgs) {
+        return 0;
+    }
+    if (kvm_enabled()) {
+        return s390_pv_kvm_init(cgs, errp);
+    }
+
+    error_setg(errp, "Protected Virtualization requires KVM");
+    return -1;
+}
+
 #endif /* HW_S390_PV_H */