> We have some special RAM memory regions (managed by virtio-mem), whereby
> the guest agreed to only use selected memory ranges. "unused" parts are
> discarded so they won't consume memory - to logically unplug these memory
> ranges. Before the VM is allowed to use such logically unplugged memory
> again, coordination with the hypervisor is required.
>
> This results in "sparse" mmaps/RAMBlocks/memory regions, whereby only
> coordinated parts are valid to be used/accessed by the VM.
>
> In most cases, we don't care about that - e.g., in KVM, we simply have a
> single KVM memory slot. However, in case of vfio, registering the
> whole region with the kernel results in all pages getting pinned, and
> therefore an unexpected high memory consumption - discarding of RAM in
> that context is broken.
>
> Let's introduce a way to coordinate discarding/populating memory within a
> RAM memory region with such special consumers of RAM memory regions: they
> can register as listeners and get updates on memory getting discarded and
> populated. Using this machinery, vfio will be able to map only the
> currently populated parts, resulting in discarded parts not getting pinned
> and not consuming memory.
>
> A RamDiscardMgr has to be set for a memory region before it is getting
> mapped, and cannot change while the memory region is mapped.
>
> Note: At some point, we might want to let RAMBlock users (esp. vfio used
> for nvme://) consume this interface as well. We'll need RAMBlock notifier
> calls when a RAMBlock is getting mapped/unmapped (via the corresponding
> memory region), so we can properly register a listener there as well.
>
> Cc: Paolo Bonzini <pbonz...@redhat.com>
> Cc: "Michael S. Tsirkin" <m...@redhat.com>
> Cc: Alex Williamson <alex.william...@redhat.com>
> Cc: Dr. David Alan Gilbert <dgilb...@redhat.com>
> Cc: Igor Mammedov <imamm...@redhat.com>
> Cc: Pankaj Gupta <pankaj.gupta.li...@gmail.com>
> Cc: Peter Xu <pet...@redhat.com>
> Cc: Auger Eric <eric.au...@redhat.com>
> Cc: Wei Yang <richard.weiy...@linux.alibaba.com>
> Cc: teawater <teawat...@linux.alibaba.com>
> Cc: Marek Kedzierski <mkedz...@redhat.com>
> Signed-off-by: David Hildenbrand <da...@redhat.com>
> ---
> include/exec/memory.h | 231 ++++++++++++++++++++++++++++++++++++++++++
> softmmu/memory.c | 22 ++++
> 2 files changed, 253 insertions(+)
>
> diff --git a/include/exec/memory.h b/include/exec/memory.h
> index 0f3e6bcd5e..30d4fcd2c0 100644
> --- a/include/exec/memory.h
> +++ b/include/exec/memory.h
> @@ -42,6 +42,12 @@ typedef struct IOMMUMemoryRegionClass
> IOMMUMemoryRegionClass;
> DECLARE_OBJ_CHECKERS(IOMMUMemoryRegion, IOMMUMemoryRegionClass,
> IOMMU_MEMORY_REGION, TYPE_IOMMU_MEMORY_REGION)
>
> +#define TYPE_RAM_DISCARD_MGR "qemu:ram-discard-mgr"
> +typedef struct RamDiscardMgrClass RamDiscardMgrClass;
> +typedef struct RamDiscardMgr RamDiscardMgr;
> +DECLARE_OBJ_CHECKERS(RamDiscardMgr, RamDiscardMgrClass, RAM_DISCARD_MGR,
> + TYPE_RAM_DISCARD_MGR);
> +
> #ifdef CONFIG_FUZZ
> void fuzz_dma_read_cb(size_t addr,
> size_t len,
> @@ -116,6 +122,66 @@ struct IOMMUNotifier {
> };
> typedef struct IOMMUNotifier IOMMUNotifier;
>
> +struct RamDiscardListener;
> +typedef int (*NotifyRamPopulate)(struct RamDiscardListener *rdl,
> + const MemoryRegion *mr, ram_addr_t offset,
> + ram_addr_t size);
> +typedef void (*NotifyRamDiscard)(struct RamDiscardListener *rdl,
> + const MemoryRegion *mr, ram_addr_t offset,
> + ram_addr_t size);
> +typedef void (*NotifyRamDiscardAll)(struct RamDiscardListener *rdl,
> + const MemoryRegion *mr);
> +
> +typedef struct RamDiscardListener {
> + /*
> + * @notify_populate:
> + *
> + * Notification that previously discarded memory is about to get
> populated.
> + * Listeners are able to object. If any listener objects, already
> + * successfully notified listeners are notified about a discard again.
> + *
> + * @rdl: the #RamDiscardListener getting notified
> + * @mr: the relevant #MemoryRegion
> + * @offset: offset into the #MemoryRegion, aligned to minimum
> granularity of
> + * the #RamDiscardMgr
> + * @size: the size, aligned to minimum granularity of the #RamDiscardMgr
> + *
> + * Returns 0 on success. If the notification is rejected by the listener,
> + * an error is returned.
> + */
> + NotifyRamPopulate notify_populate;
> +
> + /*
> + * @notify_discard:
> + *
> + * Notification that previously populated memory was discarded
> successfully
> + * and listeners should drop all references to such memory and prevent
> + * new population (e.g., unmap).
> + *
> + * @rdl: the #RamDiscardListener getting notified
> + * @mr: the relevant #MemoryRegion
> + * @offset: offset into the #MemoryRegion, aligned to minimum
> granularity of
> + * the #RamDiscardMgr
> + * @size: the size, aligned to minimum granularity of the #RamDiscardMgr
> + */
> + NotifyRamDiscard notify_discard;
> +
> + /*
> + * @notify_discard_all:
> + *
> + * Notification that all previously populated memory was discarded
> + * successfully.
> + *
> + * Note: this callback is optional. If not set, individual
> notify_populate()
> + * notifications are triggered.
> + *
> + * @rdl: the #RamDiscardListener getting notified
> + * @mr: the relevant #MemoryRegion
> + */
> + NotifyRamDiscardAll notify_discard_all;
> + QLIST_ENTRY(RamDiscardListener) next;
> +} RamDiscardListener;
> +
> /* RAM is pre-allocated and passed into qemu_ram_alloc_from_ptr */
> #define RAM_PREALLOC (1 << 0)
>
> @@ -151,6 +217,16 @@ static inline void iommu_notifier_init(IOMMUNotifier *n,
> IOMMUNotify fn,
> n->iommu_idx = iommu_idx;
> }
>
> +static inline void ram_discard_listener_init(RamDiscardListener *rdl,
> + NotifyRamPopulate populate_fn,
> + NotifyRamDiscard discard_fn,
> + NotifyRamDiscardAll
> discard_all_fn)
> +{
> + rdl->notify_populate = populate_fn;
> + rdl->notify_discard = discard_fn;
> + rdl->notify_discard_all = discard_all_fn;
> +}
> +
> /*
> * Memory region callbacks
> */
> @@ -425,6 +501,126 @@ struct IOMMUMemoryRegionClass {
> Error **errp);
> };
>
> +/*
> + * RamDiscardMgrClass:
> + *
> + * A #RamDiscardMgr coordinates which parts of specific RAM #MemoryRegion
> + * regions are currently populated to be used/accessed by the VM, notifying
> + * after parts were discarded (freeing up memory) and before parts will be
> + * populated (consuming memory), to be used/acessed by the VM.
> + *
> + * A #RamDiscardMgr can only be set for a RAM #MemoryRegion while the
> + * #MemoryRegion isn't mapped yet; it cannot change while the #MemoryRegion
> is
> + * mapped.
> + *
> + * The #RamDiscardMgr is intended to be used by technologies that are
> + * incompatible with discarding of RAM (e.g., VFIO, which may pin all
> + * memory inside a #MemoryRegion), and require proper coordination to only
> + * map the currently populated parts, to hinder parts that are expected to
> + * remain discarded from silently getting populated and consuming memory.
> + * Technologies that support discarding of RAM don't have to bother and can
> + * simply map the whole #MemoryRegion.
> + *
> + * An example #RamDiscardMgr is virtio-mem, which logically (un)plugs
> + * memory within an assigned RAM #MemoryRegion, coordinated with the VM.
> + * Logically unplugging memory consists of discarding RAM. The VM agreed to
> not
> + * access unplugged (discarded) memory - especially via DMA. virtio-mem will
> + * properly coordinate with listeners before memory is plugged (populated),
> + * and after memory is unplugged (discarded).
> + *
> + * Listeners are called in multiples of the minimum granularity and changes
> are
> + * aligned to the minimum granularity within the #MemoryRegion. Listeners
> have
> + * to prepare for memory becomming discarded in a different granularity than
> it
> + * was populated and the other way around.
> + */
> +struct RamDiscardMgrClass {
> + /* private */
> + InterfaceClass parent_class;
> +
> + /* public */
> +
> + /**
> + * @get_min_granularity:
> + *
> + * Get the minimum granularity in which listeners will get notified
> + * about changes within the #MemoryRegion via the #RamDiscardMgr.
> + *
> + * @rdm: the #RamDiscardMgr
> + * @mr: the #MemoryRegion
> + *
> + * Returns the minimum granularity.
> + */
> + uint64_t (*get_min_granularity)(const RamDiscardMgr *rdm,
> + const MemoryRegion *mr);
> +
> + /**
> + * @is_populated:
> + *
> + * Check whether the given range within the #MemoryRegion is completely
> + * populated (i.e., no parts are currently discarded). There are no
> + * alignment requirements for the range.
> + *
> + * @rdm: the #RamDiscardMgr
> + * @mr: the #MemoryRegion
> + * @offset: offset into the #MemoryRegion
> + * @size: size in the #MemoryRegion
> + *
> + * Returns whether the given range is completely populated.
> + */
> + bool (*is_populated)(const RamDiscardMgr *rdm, const MemoryRegion *mr,
> + ram_addr_t start, ram_addr_t offset);
> +
> + /**
> + * @register_listener:
> + *
> + * Register a #RamDiscardListener for a #MemoryRegion via the
> + * #RamDiscardMgr and immediately notify the #RamDiscardListener about
> all
> + * populated parts within the #MemoryRegion via the #RamDiscardMgr.
> + *
> + * In case any notification fails, no further notifications are triggered
> + * and an error is logged.
> + *
> + * @rdm: the #RamDiscardMgr
> + * @mr: the #MemoryRegion
> + * @rdl: the #RamDiscardListener
> + */
> + void (*register_listener)(RamDiscardMgr *rdm, const MemoryRegion *mr,
> + RamDiscardListener *rdl);
> +
> + /**
> + * @unregister_listener:
> + *
> + * Unregister a previously registered #RamDiscardListener for a
> + * #MemoryRegion via the #RamDiscardMgr after notifying the
> + * #RamDiscardListener about all populated parts becoming unpopulated
> + * within the #MemoryRegion via the #RamDiscardMgr.
> + *
> + * @rdm: the #RamDiscardMgr
> + * @mr: the #MemoryRegion
> + * @rdl: the #RamDiscardListener
> + */
> + void (*unregister_listener)(RamDiscardMgr *rdm, const MemoryRegion *mr,
> + RamDiscardListener *rdl);
> +
> + /**
> + * @replay_populated:
> + *
> + * Notify the #RamDiscardListener about all populated parts within the
> + * #MemoryRegion via the #RamDiscardMgr.
> + *
> + * In case any notification fails, no further notifications are
> triggered.
> + * The listener is not required to be registered.
> + *
> + * @rdm: the #RamDiscardMgr
> + * @mr: the #MemoryRegion
> + * @rdl: the #RamDiscardListener
> + *
> + * Returns 0 on success, or a negative error if any notification failed.
> + */
> + int (*replay_populated)(const RamDiscardMgr *rdm, const MemoryRegion *mr,
> + RamDiscardListener *rdl);
> +};
> +
> typedef struct CoalescedMemoryRange CoalescedMemoryRange;
> typedef struct MemoryRegionIoeventfd MemoryRegionIoeventfd;
>
> @@ -471,6 +667,7 @@ struct MemoryRegion {
> const char *name;
> unsigned ioeventfd_nb;
> MemoryRegionIoeventfd *ioeventfds;
> + RamDiscardMgr *rdm; /* Only for RAM */
> };
>
> struct IOMMUMemoryRegion {
> @@ -1965,6 +2162,40 @@ bool memory_region_present(MemoryRegion *container,
> hwaddr addr);
> */
> bool memory_region_is_mapped(MemoryRegion *mr);
>
> +/**
> + * memory_region_get_ram_discard_mgr: get the #RamDiscardMgr for a
> + * #MemoryRegion
> + *
> + * The #RamDiscardMgr cannot change while a memory region is mapped.
> + *
> + * @mr: the #MemoryRegion
> + */
> +RamDiscardMgr *memory_region_get_ram_discard_mgr(MemoryRegion *mr);
> +
> +/**
> + * memory_region_has_ram_discard_mgr: check whether a #MemoryRegion has a
> + * #RamDiscardMgr assigned
> + *
> + * @mr: the #MemoryRegion
> + */
> +static inline bool memory_region_has_ram_discard_mgr(MemoryRegion *mr)
> +{
> + return !!memory_region_get_ram_discard_mgr(mr);
> +}
> +
> +/**
> + * memory_region_set_ram_discard_mgr: set the #RamDiscardMgr for a
> + * #MemoryRegion
> + *
> + * This function must not be called for a mapped #MemoryRegion, a
> #MemoryRegion
> + * that does not cover RAM, or a #MemoryRegion that already has a
> + * #RamDiscardMgr assigned.
> + *
> + * @mr: the #MemoryRegion
> + * @urn: #RamDiscardMgr to set
> + */
> +void memory_region_set_ram_discard_mgr(MemoryRegion *mr, RamDiscardMgr *rdm);
> +
> /**
> * memory_region_find: translate an address/size relative to a
> * MemoryRegion into a #MemoryRegionSection.
> diff --git a/softmmu/memory.c b/softmmu/memory.c
> index 11ca94d037..2f1fefb806 100644
> --- a/softmmu/memory.c
> +++ b/softmmu/memory.c
> @@ -2020,6 +2020,21 @@ int memory_region_iommu_num_indexes(IOMMUMemoryRegion
> *iommu_mr)
> return imrc->num_indexes(iommu_mr);
> }
>
> +RamDiscardMgr *memory_region_get_ram_discard_mgr(MemoryRegion *mr)
> +{
> + if (!memory_region_is_mapped(mr) || !memory_region_is_ram(mr)) {
> + return NULL;
> + }
> + return mr->rdm;
> +}
> +
> +void memory_region_set_ram_discard_mgr(MemoryRegion *mr, RamDiscardMgr *rdm)
> +{
> + g_assert(memory_region_is_ram(mr) && !memory_region_is_mapped(mr));
> + g_assert(!rdm || !mr->rdm);
> + mr->rdm = rdm;
> +}
> +
> void memory_region_set_log(MemoryRegion *mr, bool log, unsigned client)
> {
> uint8_t mask = 1 << client;
> @@ -3301,10 +3316,17 @@ static const TypeInfo iommu_memory_region_info = {
> .abstract = true,
> };
>
> +static const TypeInfo ram_discard_mgr_info = {
> + .parent = TYPE_INTERFACE,
> + .name = TYPE_RAM_DISCARD_MGR,
> + .class_size = sizeof(RamDiscardMgrClass),
> +};
> +
> static void memory_register_types(void)
> {
> type_register_static(&memory_region_info);
> type_register_static(&iommu_memory_region_info);
> + type_register_static(&ram_discard_mgr_info);
> }
>
> type_init(memory_register_types)
> --
Class structures and all the stubs looks good to me.
Reviewed-by: Pankaj Gupta <pankaj.gu...@cloud.ionos.com>
> 2.28.0
>
