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

[Xiaoyao Li]

On 8/2/2023 1:21 AM, David Hildenbrand wrote:
> On 31.07.23 18:21, Xiaoyao Li wrote:
> > From: Isaku Yamahata <isaku.yamahata@intel.com>
> >
> > Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
> > Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
> > ---
> >   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.

> That all should go into the surprisingly empty patch description.

I'm sorry. I admit the empty commit message is really bad.