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Sampat wrote: >> Hi David, >> >> On 11/28/25 3:34 AM, David Hildenbrand (Red Hat) wrote: >>> 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? >> >> That's true. We are certainly thinking about how the RAM discard manager >> should look like with multiple states to allow guest_memfd and >> virtio-mem to work together. >> > > Right, there is the QEMU side of it as well. > >> Since both paths in Linux eventually converge around >> add_memory_resource(), based on some light hacking in QEMU I could see >> similar hotplug behavior for virtio-mem as well. > > For virtio-mem it would not be add_memory_resource(). > > Whenever we would be plugging memory we would be accepting it, and when we would be unplugging memory we would unaccept it. > > That is, acceptance does not happen at add_memory_resource() time, but when virtio-mem asks the device to transition a device block from unplugged<->plugged. Ah, I see. Thanks for clearing that up!