details: Strip back 'Enable shared memory' to only cover memfd

Strip back the logic to:

* Only try to toggle source_type=memfd and access_mode=shared
* Disable the field if guest has any <numa> config
* Disable the field if domcaps does not report virtiofs and memfd

This is the simplest future proof case, though it will exclude some
legit guest configs and some libvirt+qemu back compat.

My feeling is the <numa> stuff in particular is pretty advanced, so if
users have it configured they can toggle shared memory via the XML
without too much trouble.

Signed-off-by: Cole Robinson <crobinso@redhat.com>

virtManager/object/domain.py

@@ -446,23 +446,17 @@ class vmmDomain(vmmLibvirtObject):
         Return a value for 'Enable shared memory' UI, and an error if
         the value is not editable
         """
+        is_shared = False
         err = None
+        domcaps = self.get_domain_capabilities()
 
-        # If virtiofs support is reported via domcapabilities, It's seen as
-        # libvirt is new enough to allow setting shared memory access without
-        # hugepages or numa config.
-        if not self.get_domain_capabilities().supports_filesystem_virtiofs():
-            is_shared = self.xmlobj.cpu.all_shared_memAccess_cells()
-            err = _("Libvirt may not be new enough to support shared memory")
-
+        if self.xmlobj.cpu.cells:
+            err = _("Can not change shared memory setting when <numa> is configured.")
+        elif (not domcaps.supports_filesystem_virtiofs() or
+              not domcaps.supports_memorybacking_memfd()):
+            err = _("Libvirt may not be new enough to support memfd.")
         else:
-            is_shared = (self.xmlobj.memoryBacking.is_shared_access() or
-                         self.xmlobj.cpu.all_shared_memAccess_cells())
-            # The access mode can be overridden per numa node by memAccess, So
-            # we need to check whether it has 'private' memAccess in numa node.
-            if self.xmlobj.cpu.has_private_memAccess_cells():
-                is_shared = False
-                err = _("memory access mode 'private' is found in numa node")
+            is_shared = self.xmlobj.memoryBacking.source_type == "memfd"
 
         return is_shared, err
 
@@ -680,19 +674,11 @@ class vmmDomain(vmmLibvirtObject):
     def _edit_shared_mem(self, guest, mem_shared):
         source_type = _SENTINEL
         access_mode = _SENTINEL
-        memAccess = _SENTINEL
 
         if mem_shared:
-            if guest.cpu.has_private_memAccess_cells():
-                memAccess = "shared"
-            if self.get_domain_capabilities().supports_memorybacking_memfd():
-                source_type = "memfd"
-            else:
-                source_type = "file"
+            source_type = "memfd"
             access_mode = "shared"
         else:
-            if guest.cpu.all_shared_memAccess_cells():
-                memAccess = None
             source_type = None
             access_mode = None
 
@@ -700,9 +686,6 @@ class vmmDomain(vmmLibvirtObject):
             guest.memoryBacking.source_type = source_type
         if access_mode != _SENTINEL:
             guest.memoryBacking.access_mode = access_mode
-        if memAccess != _SENTINEL:
-            for cell in guest.cpu.cells:
-                cell.memAccess = memAccess
 
     def define_memory(self, memory=_SENTINEL, maxmem=_SENTINEL,
             mem_shared=_SENTINEL):

virtinst/domain/cpu.py

@@ -412,20 +412,6 @@ class DomainCpu(XMLBuilder):
             return
         self.topology.set_defaults_from_vcpus(vcpus)
 
-    def has_private_memAccess_cells(self):
-        for cell in self.cells:
-            if cell.memAccess == "private":
-                return True
-        return False
-
-    def all_shared_memAccess_cells(self):
-        if not self.cells:
-            return False
-        for cell in self.cells:
-            if cell.memAccess != "shared":
-                return False
-        return True
-
 
     ##################
     # Default config #

virtinst/domain/memorybacking.py

@@ -36,6 +36,3 @@ class DomainMemoryBacking(XMLBuilder):
     allocation_mode = XMLProperty("./allocation/@mode")
 
     pages = XMLChildProperty(_HugepagesPage, relative_xpath="./hugepages")
-
-    def is_shared_access(self):
-        return self.access_mode == "shared"