i386/sev: Introduce "sev-common" type to encapsulate common SEV state

Currently all SEV/SEV-ES functionality is managed through a single
'sev-guest' QOM type. With upcoming support for SEV-SNP, taking this
same approach won't work well since some of the properties/state
managed by 'sev-guest' is not applicable to SEV-SNP, which will instead
rely on a new QOM type with its own set of properties/state.

To prepare for this, this patch moves common state into an abstract
'sev-common' parent type to encapsulate properties/state that are
common to both SEV/SEV-ES and SEV-SNP, leaving only SEV/SEV-ES-specific
properties/state in the current 'sev-guest' type. This should not
affect current behavior or command-line options.

As part of this patch, some related changes are also made:

  - a static 'sev_guest' variable is currently used to keep track of
    the 'sev-guest' instance. SEV-SNP would similarly introduce an
    'sev_snp_guest' static variable. But these instances are now
    available via qdev_get_machine()->cgs, so switch to using that
    instead and drop the static variable.

  - 'sev_guest' is currently used as the name for the static variable
    holding a pointer to the 'sev-guest' instance. Re-purpose the name
    as a local variable referring the 'sev-guest' instance, and use
    that consistently throughout the code so it can be easily
    distinguished from sev-common/sev-snp-guest instances.

  - 'sev' is generally used as the name for local variables holding a
    pointer to the 'sev-guest' instance. In cases where that now points
    to common state, use the name 'sev_common'; in cases where that now
    points to state specific to 'sev-guest' instance, use the name
    'sev_guest'

In order to enable kernel-hashes for SNP, pull it from
SevGuestProperties to its parent SevCommonProperties so
it will be available for both SEV and SNP.

Signed-off-by: Michael Roth <michael.roth@amd.com>
Co-developed-by: Dov Murik <dovmurik@linux.ibm.com>
Signed-off-by: Dov Murik <dovmurik@linux.ibm.com>
Acked-by: Markus Armbruster <armbru@redhat.com> (QAPI schema)
Co-developed-by: Pankaj Gupta <pankaj.gupta@amd.com>
Signed-off-by: Pankaj Gupta <pankaj.gupta@amd.com>
Message-ID: <20240530111643.1091816-5-pankaj.gupta@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

qapi/qom.json

@@ -875,20 +875,12 @@
   'data': { '*filename': 'str' } }
 
 ##
-# @SevGuestProperties:
+# @SevCommonProperties:
 #
-# Properties for sev-guest objects.
+# Properties common to objects that are derivatives of sev-common.
 #
 # @sev-device: SEV device to use (default: "/dev/sev")
 #
-# @dh-cert-file: guest owners DH certificate (encoded with base64)
-#
-# @session-file: guest owners session parameters (encoded with base64)
-#
-# @policy: SEV policy value (default: 0x1)
-#
-# @handle: SEV firmware handle (default: 0)
-#
 # @cbitpos: C-bit location in page table entry (default: 0)
 #
 # @reduced-phys-bits: number of bits in physical addresses that become
@@ -898,6 +890,27 @@
 #     designated guest firmware page for measured boot with -kernel
 #     (default: false) (since 6.2)
 #
+# Since: 9.1
+##
+{ 'struct': 'SevCommonProperties',
+  'data': { '*sev-device': 'str',
+            '*cbitpos': 'uint32',
+            'reduced-phys-bits': 'uint32',
+            '*kernel-hashes': 'bool' } }
+
+##
+# @SevGuestProperties:
+#
+# Properties for sev-guest objects.
+#
+# @dh-cert-file: guest owners DH certificate (encoded with base64)
+#
+# @session-file: guest owners session parameters (encoded with base64)
+#
+# @policy: SEV policy value (default: 0x1)
+#
+# @handle: SEV firmware handle (default: 0)
+#
 # @legacy-vm-type: Use legacy KVM_SEV_INIT KVM interface for creating the VM.
 #                  The newer KVM_SEV_INIT2 interface syncs additional vCPU
 #                  state when initializing the VMSA structures, which will
@@ -909,14 +922,11 @@
 # Since: 2.12
 ##
 { 'struct': 'SevGuestProperties',
-  'data': { '*sev-device': 'str',
-            '*dh-cert-file': 'str',
+  'base': 'SevCommonProperties',
+  'data': { '*dh-cert-file': 'str',
             '*session-file': 'str',
             '*policy': 'uint32',
             '*handle': 'uint32',
-            '*cbitpos': 'uint32',
-            'reduced-phys-bits': 'uint32',
-            '*kernel-hashes': 'bool',
             '*legacy-vm-type': 'bool' } }
 
 ##

target/i386/sev.h

@@ -20,6 +20,9 @@
 
 #include "exec/confidential-guest-support.h"
 
+#define TYPE_SEV_COMMON "sev-common"
+#define TYPE_SEV_GUEST "sev-guest"
+
 #define SEV_POLICY_NODBG        0x1
 #define SEV_POLICY_NOKS         0x2
 #define SEV_POLICY_ES           0x4