Re: [RFC PATCH 08/19] HostMem: Add private property to indicate to use kvm gmem

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On 02.08.23 10:03, Xiaoyao Li wrote:
On 8/2/2023 1:21 AM, David Hildenbrand wrote:
On 31.07.23 18:21, Xiaoyao Li wrote:
From: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>

Signed-off-by: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
Signed-off-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
---
   backends/hostmem.c       | 18 ++++++++++++++++++
   include/sysemu/hostmem.h |  2 +-
   qapi/qom.json            |  4 ++++
   3 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/backends/hostmem.c b/backends/hostmem.c
index 747e7838c031..dbdbb0aafd45 100644
--- a/backends/hostmem.c
+++ b/backends/hostmem.c
@@ -461,6 +461,20 @@ static void
host_memory_backend_set_reserve(Object *o, bool value, Error **errp)
       }
       backend->reserve = value;
   }
+
+static bool host_memory_backend_get_private(Object *o, Error **errp)
+{
+    HostMemoryBackend *backend = MEMORY_BACKEND(o);
+
+    return backend->private;
+}
+
+static void host_memory_backend_set_private(Object *o, bool value,
Error **errp)
+{
+    HostMemoryBackend *backend = MEMORY_BACKEND(o);
+
+    backend->private = value;
+}
   #endif /* CONFIG_LINUX */
   static bool
@@ -541,6 +555,10 @@ host_memory_backend_class_init(ObjectClass *oc,
void *data)
           host_memory_backend_get_reserve,
host_memory_backend_set_reserve);
       object_class_property_set_description(oc, "reserve",
           "Reserve swap space (or huge pages) if applicable");
+    object_class_property_add_bool(oc, "private",
+        host_memory_backend_get_private,
host_memory_backend_set_private);
+    object_class_property_set_description(oc, "private",
+        "Use KVM gmem private memory");
   #endif /* CONFIG_LINUX */
       /*
        * Do not delete/rename option. This option must be considered
stable
diff --git a/include/sysemu/hostmem.h b/include/sysemu/hostmem.h
index 39326f1d4f9c..d88970395618 100644
--- a/include/sysemu/hostmem.h
+++ b/include/sysemu/hostmem.h
@@ -65,7 +65,7 @@ struct HostMemoryBackend {
       /* protected */
       uint64_t size;
       bool merge, dump, use_canonical_path;
-    bool prealloc, is_mapped, share, reserve;
+    bool prealloc, is_mapped, share, reserve, private;
       uint32_t prealloc_threads;
       ThreadContext *prealloc_context;
       DECLARE_BITMAP(host_nodes, MAX_NODES + 1);
diff --git a/qapi/qom.json b/qapi/qom.json
index 7f92ea43e8e1..e0b2044e3d20 100644
--- a/qapi/qom.json
+++ b/qapi/qom.json
@@ -605,6 +605,9 @@
   # @reserve: if true, reserve swap space (or huge pages) if applicable
   #     (default: true) (since 6.1)
   #
+# @private: if true, use KVM gmem private memory
+#           (default: false) (since 8.1)
+#

But that's not what any of this does.

This patch only adds a property and doesn't even explain what it intends
to achieve with that.

How will it be used from a user? What will it affect internally? What
will it modify in regards of the memory backend?

How it will be used is in the next patch, patch 09.

for kvm_x86_sw_protected_vm type VM, it will allocate private gmem with
KVM ioctl if the memory backend has property "private" on.

It feels wired up the wrong way.

When creating/initializing the memory backend, we should also take care of allocating the gmem_fd, for example, by doing some gmem allocation callback, ideally *internally* creating the RAM memory region / RAMBlock.

And we should fail if that is impossible (gmem does not apply to the VM) or creating the gmem_fd failed for other reason.

Like passing a RAM_GMEM flag to memory_region_init_ram_flags_nomigrate() in ram_backend_memory_alloc(), to then handle it internally, failing if there is an error.

--
Cheers,

David / dhildenb




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