Re: [RFC PATCH 2/4] mm: Add support for unaccepted memory hotplug

[David Hildenbrand (Red Hat)]

On 11/27/25 18:40, Kiryl Shutsemau wrote:
> On Wed, Nov 26, 2025 at 04:27:29PM -0600, Pratik R. Sampat wrote:
> > On 11/26/25 5:12 AM, Kiryl Shutsemau wrote:
> > > On Tue, Nov 25, 2025 at 11:57:51AM -0600, Pratik R. Sampat wrote:
> > > > The unaccepted memory structure currently only supports accepting memory
> > > > present at boot time. The unaccepted table uses a fixed-size bitmap
> > > > reserved in memblock based on the initial memory layout, preventing
> > > > dynamic addition of memory ranges after boot. This causes guest
> > > > termination when memory is hot-added in a secure virtual machine due to
> > > > accessing pages that have not transitioned to private before use.
> > >
> > > How does the hot-pluggable memory look in EFI memory map? I thought
> > > hot-pluggable ranges suppose to be declared thare. The cleanest solution
> > > would be to have hot-pluggable and unaccepted indicated in EFI memory,
> > > so we can size bitmap accordingly upfront.
> >
> > I'm not quite sure if I fully understand. Do you mean to refer to the
> > EFI_MEMORY_HOT_PLUGGABLE attribute that is used for cold plugged boot
> > memory? If so, wouldn't it still be desirable to increase the size of
> > the bitmap to what was marked as hotpluggable initially?
>
> I just don't understand how hotpluggable memory presented in EFI memory
> map in presence of unaccepted memory. If not-yet-plugged memory marked
> as unaccepted we can preallocate bitmap upfront and make unaccepted
> memory transparent wrt hotplug.
>
> BTW, isn't virtio-mem a more attractive target to support than HW-style
> hotplug?

I would have thought so as well, such that we can just let virtio-mem 
take care of any acceptance before actually using hotplugged memory 
(exposing it to the buddy).

Likely there is desire to support other hypervisors?

--
Cheers

David