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memory-device,vhost: Support memory devices that dynamically consume memslots

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We want to support memory devices that have a dynamically managed memory
region container as device memory region. This device memory region maps
multiple RAM memory subregions (e.g., aliases to the same RAM memory
region), whereby these subregions can be (un)mapped on demand.

Each RAM subregion will consume a memslot in KVM and vhost, resulting in
such a new device consuming memslots dynamically, and initially usually
0. We already track the number of used vs. required memslots for all
memslots. From that, we can derive the number of reserved memslots that
must not be used otherwise.

The target use case is virtio-mem and the hyper-v balloon, which will
dynamically map aliases to RAM memory region into their device memory
region container.

Properly document what's supported and what's not and extend the vhost
memslot check accordingly.

Message-ID: <20230926185738.277351-10-david@redhat.com>
Reviewed-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
This commit is contained in:
David Hildenbrand 2023-09-26 20:57:29 +02:00
parent f9716f4b0d
commit 766aa0a654
4 changed files with 53 additions and 6 deletions
Download patch file Download diff file Expand all files Collapse all files

7
include/hw/mem/memory-device.h
View file

@ -46,6 +46,12 @@ typedef struct MemoryDeviceState MemoryDeviceState;
* single RAM memory region or a memory region container with subregions
* that are RAM memory regions or aliases to RAM memory regions. Other
* memory regions or subregions are not supported.
*
* If the device memory region returned via @get_memory_region is a
* memory region container, it's supported to dynamically (un)map subregions
* as long as the number of memslots returned by @get_memslots() won't
* be exceeded and as long as all memory regions are of the same kind (e.g.,
* all RAM or all ROM).
*/
struct MemoryDeviceClass {
/* private */
@ -125,6 +131,7 @@ struct MemoryDeviceClass {
MemoryDeviceInfoList *qmp_memory_device_list(void);
uint64_t get_plugged_memory_size(void);
unsigned int memory_devices_get_reserved_memslots(void);
void memory_device_pre_plug(MemoryDeviceState *md, MachineState *ms,
const uint64_t *legacy_align, Error **errp);
void memory_device_plug(MemoryDeviceState *md, MachineState *ms);