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MM - The Memory Manager

The memory manager is in charge of the following memory:

The global memory manager (GMM) is the global counter part / partner of MM. MM will provide therefore ring-3 callable interfaces for some of the GMM APIs related to resource tracking (PGM is the user).

See also:
The Memory Manager API

Hypervisor Memory Area

The HMA is used when executing in raw-mode. We borrow, with the help of PGMMap, some unused space (one or more page directory entries to be precise) in the guest's virtual memory context. PGM will monitor the guest's virtual address space for changes and relocate the HMA when required.

To give some idea what's in the HMA, study the 'info hma' output:

VBoxDbg> info hma
Hypervisor Memory Area (HMA) Layout: Base 00000000a0000000, 0x00800000 bytes
00000000a05cc000-00000000a05cd000                  DYNAMIC                  fence
00000000a05c4000-00000000a05cc000                  DYNAMIC                  Dynamic mapping
00000000a05c3000-00000000a05c4000                  DYNAMIC                  fence
00000000a05b8000-00000000a05c3000                  DYNAMIC                  Paging
00000000a05b6000-00000000a05b8000                  MMIO2   0000000000000000 PCNetShMem
00000000a0536000-00000000a05b6000                  MMIO2   0000000000000000 VGA VRam
00000000a0523000-00000000a0536000 00002aaab3d0c000 LOCKED  autofree         alloc once (PDM_DEVICE)
00000000a0522000-00000000a0523000                  DYNAMIC                  fence
00000000a051e000-00000000a0522000 00002aaab36f5000 LOCKED  autofree         VBoxDD2GC.gc
00000000a051d000-00000000a051e000                  DYNAMIC                  fence
00000000a04eb000-00000000a051d000 00002aaab36c3000 LOCKED  autofree         VBoxDDGC.gc
00000000a04ea000-00000000a04eb000                  DYNAMIC                  fence
00000000a04e9000-00000000a04ea000 00002aaab36c2000 LOCKED  autofree         ram range (High ROM Region)
00000000a04e8000-00000000a04e9000                  DYNAMIC                  fence
00000000a040e000-00000000a04e8000 00002aaab2e6d000 LOCKED  autofree         VMMGC.gc
00000000a0208000-00000000a040e000 00002aaab2c67000 LOCKED  autofree         alloc once (PATM)
00000000a01f7000-00000000a0208000 00002aaaab92d000 LOCKED  autofree         alloc once (SELM)
00000000a01e7000-00000000a01f7000 00002aaaab5e8000 LOCKED  autofree         alloc once (SELM)
00000000a01e6000-00000000a01e7000                  DYNAMIC                  fence
00000000a01e5000-00000000a01e6000 00002aaaab5e7000 HCPHYS  00000000c363c000 Core Code
00000000a01e4000-00000000a01e5000                  DYNAMIC                  fence
00000000a01e3000-00000000a01e4000 00002aaaaab26000 HCPHYS  00000000619cf000 GIP
00000000a01a2000-00000000a01e3000 00002aaaabf32000 LOCKED  autofree         alloc once (PGM_PHYS)
00000000a016b000-00000000a01a2000 00002aaab233f000 LOCKED  autofree         alloc once (PGM_POOL)
00000000a016a000-00000000a016b000                  DYNAMIC                  fence
00000000a0165000-00000000a016a000                  DYNAMIC                  CR3 mapping
00000000a0164000-00000000a0165000                  DYNAMIC                  fence
00000000a0024000-00000000a0164000 00002aaab215f000 LOCKED  autofree         Heap
00000000a0023000-00000000a0024000                  DYNAMIC                  fence
00000000a0001000-00000000a0023000 00002aaab1d24000 LOCKED  pages            VM
00000000a0000000-00000000a0001000                  DYNAMIC                  fence

Hypervisor Heap

The heap is accessible from ring-3, ring-0 and the raw-mode context. That said, it's not necessarily mapped into ring-0 on if that's possible since we don't wish to waste kernel address space without a good reason.

Allocations within the heap are always in the same relative position in all contexts, so, it's possible to use offset based linking. In fact, the heap is internally using offset based linked lists tracking heap blocks. We use offset linked AVL trees and lists in a lot of places where share structures between RC, R3 and R0, so this is a strict requirement of the heap. However this means that we cannot easily extend the heap since the extension won't necessarily be in the continuation of the current heap memory in all (or any) context.

All allocations are tagged. Per tag allocation statistics will be maintaing and exposed thru STAM when VBOX_WITH_STATISTICS is defined.

Tagged Ring-3 Heap

The ring-3 heap is a wrapper around the RTMem API adding allocation statistics and automatic cleanup on VM destruction.

Per tag allocation statistics will be maintaing and exposed thru STAM when VBOX_WITH_STATISTICS is defined.

Page Pool

The MM manages a page pool from which other components can allocate locked, page aligned and page sized memory objects. The pool provides facilities to convert back and forth between (host) physical and virtual addresses (within the pool of course). Several specialized interfaces are provided for the most common alloctions and convertions to save the caller from bothersome casting and extra parameter passing.

Locked Process Memory

MM manages the locked process memory. This is used for a bunch of things (count the LOCKED entries in the'info hma' output found in Hypervisor Memory Area), but the main consumer of memory is currently for guest RAM. There is an ongoing rewrite that will move all the guest RAM allocation to PGM and GMM.

The locking of memory is something doing in cooperation with the VirtualBox support driver, SUPDrv (aka. VBoxDrv), thru the support library API, SUPR3 (aka. SUPLib).

Physical Guest Memory

MM is currently managing the physical memory for the guest. It relies heavily on PGM for this. There is an ongoing rewrite that will move this to PGM. (The rewrite is driven by the need for more flexible guest ram allocation, but also motivated by the fact that MMPhys is just adding stupid bureaucracy and that MMR3PhysReserve is a totally weird artifact that must go away.)

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