2011-07-26 13:26:00 +02:00
|
|
|
The memory API
|
|
|
|
==============
|
|
|
|
|
|
|
|
The memory API models the memory and I/O buses and controllers of a QEMU
|
|
|
|
machine. It attempts to allow modelling of:
|
|
|
|
|
|
|
|
- ordinary RAM
|
|
|
|
- memory-mapped I/O (MMIO)
|
|
|
|
- memory controllers that can dynamically reroute physical memory regions
|
2011-12-05 20:54:14 +01:00
|
|
|
to different destinations
|
2011-07-26 13:26:00 +02:00
|
|
|
|
|
|
|
The memory model provides support for
|
|
|
|
|
|
|
|
- tracking RAM changes by the guest
|
|
|
|
- setting up coalesced memory for kvm
|
|
|
|
- setting up ioeventfd regions for kvm
|
|
|
|
|
2013-05-06 18:23:38 +02:00
|
|
|
Memory is modelled as an acyclic graph of MemoryRegion objects. Sinks
|
|
|
|
(leaves) are RAM and MMIO regions, while other nodes represent
|
|
|
|
buses, memory controllers, and memory regions that have been rerouted.
|
|
|
|
|
|
|
|
In addition to MemoryRegion objects, the memory API provides AddressSpace
|
|
|
|
objects for every root and possibly for intermediate MemoryRegions too.
|
|
|
|
These represent memory as seen from the CPU or a device's viewpoint.
|
2011-07-26 13:26:00 +02:00
|
|
|
|
|
|
|
Types of regions
|
|
|
|
----------------
|
|
|
|
|
2016-01-28 19:54:57 +01:00
|
|
|
There are multiple types of memory regions (all represented by a single C type
|
2011-07-26 13:26:00 +02:00
|
|
|
MemoryRegion):
|
|
|
|
|
|
|
|
- RAM: a RAM region is simply a range of host memory that can be made available
|
|
|
|
to the guest.
|
2016-01-28 19:54:57 +01:00
|
|
|
You typically initialize these with memory_region_init_ram(). Some special
|
|
|
|
purposes require the variants memory_region_init_resizeable_ram(),
|
|
|
|
memory_region_init_ram_from_file(), or memory_region_init_ram_ptr().
|
2011-07-26 13:26:00 +02:00
|
|
|
|
|
|
|
- MMIO: a range of guest memory that is implemented by host callbacks;
|
|
|
|
each read or write causes a callback to be called on the host.
|
2016-04-01 12:47:57 +02:00
|
|
|
You initialize these with memory_region_init_io(), passing it a
|
|
|
|
MemoryRegionOps structure describing the callbacks.
|
2016-01-28 19:54:57 +01:00
|
|
|
|
|
|
|
- ROM: a ROM memory region works like RAM for reads (directly accessing
|
2016-07-04 14:06:35 +02:00
|
|
|
a region of host memory), and forbids writes. You initialize these with
|
|
|
|
memory_region_init_rom().
|
|
|
|
|
|
|
|
- ROM device: a ROM device memory region works like RAM for reads
|
|
|
|
(directly accessing a region of host memory), but like MMIO for
|
|
|
|
writes (invoking a callback). You initialize these with
|
|
|
|
memory_region_init_rom_device().
|
2016-01-28 19:54:57 +01:00
|
|
|
|
|
|
|
- IOMMU region: an IOMMU region translates addresses of accesses made to it
|
|
|
|
and forwards them to some other target memory region. As the name suggests,
|
|
|
|
these are only needed for modelling an IOMMU, not for simple devices.
|
|
|
|
You initialize these with memory_region_init_iommu().
|
2011-07-26 13:26:00 +02:00
|
|
|
|
|
|
|
- container: a container simply includes other memory regions, each at
|
|
|
|
a different offset. Containers are useful for grouping several regions
|
|
|
|
into one unit. For example, a PCI BAR may be composed of a RAM region
|
|
|
|
and an MMIO region.
|
|
|
|
|
|
|
|
A container's subregions are usually non-overlapping. In some cases it is
|
|
|
|
useful to have overlapping regions; for example a memory controller that
|
|
|
|
can overlay a subregion of RAM with MMIO or ROM, or a PCI controller
|
|
|
|
that does not prevent card from claiming overlapping BARs.
|
|
|
|
|
2016-01-28 19:54:57 +01:00
|
|
|
You initialize a pure container with memory_region_init().
|
|
|
|
|
2011-07-26 13:26:00 +02:00
|
|
|
- alias: a subsection of another region. Aliases allow a region to be
|
|
|
|
split apart into discontiguous regions. Examples of uses are memory banks
|
|
|
|
used when the guest address space is smaller than the amount of RAM
|
|
|
|
addressed, or a memory controller that splits main memory to expose a "PCI
|
|
|
|
hole". Aliases may point to any type of region, including other aliases,
|
|
|
|
but an alias may not point back to itself, directly or indirectly.
|
2016-01-28 19:54:57 +01:00
|
|
|
You initialize these with memory_region_init_alias().
|
|
|
|
|
|
|
|
- reservation region: a reservation region is primarily for debugging.
|
|
|
|
It claims I/O space that is not supposed to be handled by QEMU itself.
|
|
|
|
The typical use is to track parts of the address space which will be
|
2018-05-15 16:35:16 +02:00
|
|
|
handled by the host kernel when KVM is enabled. You initialize these
|
|
|
|
by passing a NULL callback parameter to memory_region_init_io().
|
2011-07-26 13:26:00 +02:00
|
|
|
|
2013-10-15 16:42:34 +02:00
|
|
|
It is valid to add subregions to a region which is not a pure container
|
|
|
|
(that is, to an MMIO, RAM or ROM region). This means that the region
|
|
|
|
will act like a container, except that any addresses within the container's
|
|
|
|
region which are not claimed by any subregion are handled by the
|
|
|
|
container itself (ie by its MMIO callbacks or RAM backing). However
|
|
|
|
it is generally possible to achieve the same effect with a pure container
|
|
|
|
one of whose subregions is a low priority "background" region covering
|
|
|
|
the whole address range; this is often clearer and is preferred.
|
|
|
|
Subregions cannot be added to an alias region.
|
2011-07-26 13:26:00 +02:00
|
|
|
|
2017-07-07 16:42:57 +02:00
|
|
|
Migration
|
|
|
|
---------
|
|
|
|
|
|
|
|
Where the memory region is backed by host memory (RAM, ROM and
|
|
|
|
ROM device memory region types), this host memory needs to be
|
|
|
|
copied to the destination on migration. These APIs which allocate
|
|
|
|
the host memory for you will also register the memory so it is
|
|
|
|
migrated:
|
|
|
|
- memory_region_init_ram()
|
|
|
|
- memory_region_init_rom()
|
|
|
|
- memory_region_init_rom_device()
|
|
|
|
|
|
|
|
For most devices and boards this is the correct thing. If you
|
|
|
|
have a special case where you need to manage the migration of
|
|
|
|
the backing memory yourself, you can call the functions:
|
|
|
|
- memory_region_init_ram_nomigrate()
|
|
|
|
- memory_region_init_rom_nomigrate()
|
|
|
|
- memory_region_init_rom_device_nomigrate()
|
|
|
|
which only initialize the MemoryRegion and leave handling
|
|
|
|
migration to the caller.
|
|
|
|
|
|
|
|
The functions:
|
|
|
|
- memory_region_init_resizeable_ram()
|
|
|
|
- memory_region_init_ram_from_file()
|
|
|
|
- memory_region_init_ram_from_fd()
|
|
|
|
- memory_region_init_ram_ptr()
|
|
|
|
- memory_region_init_ram_device_ptr()
|
|
|
|
are for special cases only, and so they do not automatically
|
|
|
|
register the backing memory for migration; the caller must
|
|
|
|
manage migration if necessary.
|
|
|
|
|
2011-07-26 13:26:00 +02:00
|
|
|
Region names
|
|
|
|
------------
|
|
|
|
|
|
|
|
Regions are assigned names by the constructor. For most regions these are
|
|
|
|
only used for debugging purposes, but RAM regions also use the name to identify
|
|
|
|
live migration sections. This means that RAM region names need to have ABI
|
|
|
|
stability.
|
|
|
|
|
|
|
|
Region lifecycle
|
|
|
|
----------------
|
|
|
|
|
2015-02-13 13:42:03 +01:00
|
|
|
A region is created by one of the memory_region_init*() functions and
|
|
|
|
attached to an object, which acts as its owner or parent. QEMU ensures
|
|
|
|
that the owner object remains alive as long as the region is visible to
|
|
|
|
the guest, or as long as the region is in use by a virtual CPU or another
|
|
|
|
device. For example, the owner object will not die between an
|
|
|
|
address_space_map operation and the corresponding address_space_unmap.
|
2014-06-11 12:42:01 +02:00
|
|
|
|
2015-02-13 13:42:03 +01:00
|
|
|
After creation, a region can be added to an address space or a
|
|
|
|
container with memory_region_add_subregion(), and removed using
|
|
|
|
memory_region_del_subregion().
|
|
|
|
|
|
|
|
Various region attributes (read-only, dirty logging, coalesced mmio,
|
|
|
|
ioeventfd) can be changed during the region lifecycle. They take effect
|
|
|
|
as soon as the region is made visible. This can be immediately, later,
|
|
|
|
or never.
|
|
|
|
|
|
|
|
Destruction of a memory region happens automatically when the owner
|
|
|
|
object dies.
|
|
|
|
|
|
|
|
If however the memory region is part of a dynamically allocated data
|
|
|
|
structure, you should call object_unparent() to destroy the memory region
|
|
|
|
before the data structure is freed. For an example see VFIOMSIXInfo
|
|
|
|
and VFIOQuirk in hw/vfio/pci.c.
|
|
|
|
|
|
|
|
You must not destroy a memory region as long as it may be in use by a
|
|
|
|
device or CPU. In order to do this, as a general rule do not create or
|
|
|
|
destroy memory regions dynamically during a device's lifetime, and only
|
|
|
|
call object_unparent() in the memory region owner's instance_finalize
|
|
|
|
callback. The dynamically allocated data structure that contains the
|
|
|
|
memory region then should obviously be freed in the instance_finalize
|
|
|
|
callback as well.
|
|
|
|
|
|
|
|
If you break this rule, the following situation can happen:
|
|
|
|
|
|
|
|
- the memory region's owner had a reference taken via memory_region_ref
|
|
|
|
(for example by address_space_map)
|
|
|
|
|
|
|
|
- the region is unparented, and has no owner anymore
|
|
|
|
|
|
|
|
- when address_space_unmap is called, the reference to the memory region's
|
|
|
|
owner is leaked.
|
|
|
|
|
|
|
|
|
|
|
|
There is an exception to the above rule: it is okay to call
|
|
|
|
object_unparent at any time for an alias or a container region. It is
|
|
|
|
therefore also okay to create or destroy alias and container regions
|
|
|
|
dynamically during a device's lifetime.
|
|
|
|
|
|
|
|
This exceptional usage is valid because aliases and containers only help
|
|
|
|
QEMU building the guest's memory map; they are never accessed directly.
|
|
|
|
memory_region_ref and memory_region_unref are never called on aliases
|
|
|
|
or containers, and the above situation then cannot happen. Exploiting
|
|
|
|
this exception is rarely necessary, and therefore it is discouraged,
|
|
|
|
but nevertheless it is used in a few places.
|
|
|
|
|
|
|
|
For regions that "have no owner" (NULL is passed at creation time), the
|
|
|
|
machine object is actually used as the owner. Since instance_finalize is
|
|
|
|
never called for the machine object, you must never call object_unparent
|
|
|
|
on regions that have no owner, unless they are aliases or containers.
|
2014-06-11 12:42:01 +02:00
|
|
|
|
2011-07-26 13:26:00 +02:00
|
|
|
|
|
|
|
Overlapping regions and priority
|
|
|
|
--------------------------------
|
|
|
|
Usually, regions may not overlap each other; a memory address decodes into
|
|
|
|
exactly one target. In some cases it is useful to allow regions to overlap,
|
|
|
|
and sometimes to control which of an overlapping regions is visible to the
|
|
|
|
guest. This is done with memory_region_add_subregion_overlap(), which
|
|
|
|
allows the region to overlap any other region in the same container, and
|
|
|
|
specifies a priority that allows the core to decide which of two regions at
|
|
|
|
the same address are visible (highest wins).
|
2013-09-16 10:21:15 +02:00
|
|
|
Priority values are signed, and the default value is zero. This means that
|
|
|
|
you can use memory_region_add_subregion_overlap() both to specify a region
|
|
|
|
that must sit 'above' any others (with a positive priority) and also a
|
|
|
|
background region that sits 'below' others (with a negative priority).
|
2011-07-26 13:26:00 +02:00
|
|
|
|
2013-10-15 16:42:34 +02:00
|
|
|
If the higher priority region in an overlap is a container or alias, then
|
|
|
|
the lower priority region will appear in any "holes" that the higher priority
|
|
|
|
region has left by not mapping subregions to that area of its address range.
|
|
|
|
(This applies recursively -- if the subregions are themselves containers or
|
|
|
|
aliases that leave holes then the lower priority region will appear in these
|
|
|
|
holes too.)
|
|
|
|
|
|
|
|
For example, suppose we have a container A of size 0x8000 with two subregions
|
2016-02-26 09:40:51 +01:00
|
|
|
B and C. B is a container mapped at 0x2000, size 0x4000, priority 2; C is
|
|
|
|
an MMIO region mapped at 0x0, size 0x6000, priority 1. B currently has two
|
2013-10-15 16:42:34 +02:00
|
|
|
of its own subregions: D of size 0x1000 at offset 0 and E of size 0x1000 at
|
|
|
|
offset 0x2000. As a diagram:
|
|
|
|
|
2016-03-22 10:45:54 +01:00
|
|
|
0 1000 2000 3000 4000 5000 6000 7000 8000
|
|
|
|
|------|------|------|------|------|------|------|------|
|
|
|
|
A: [ ]
|
2013-10-15 16:42:34 +02:00
|
|
|
C: [CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC]
|
|
|
|
B: [ ]
|
|
|
|
D: [DDDDD]
|
|
|
|
E: [EEEEE]
|
|
|
|
|
|
|
|
The regions that will be seen within this address range then are:
|
|
|
|
[CCCCCCCCCCCC][DDDDD][CCCCC][EEEEE][CCCCC]
|
|
|
|
|
|
|
|
Since B has higher priority than C, its subregions appear in the flat map
|
|
|
|
even where they overlap with C. In ranges where B has not mapped anything
|
|
|
|
C's region appears.
|
|
|
|
|
|
|
|
If B had provided its own MMIO operations (ie it was not a pure container)
|
|
|
|
then these would be used for any addresses in its range not handled by
|
|
|
|
D or E, and the result would be:
|
|
|
|
[CCCCCCCCCCCC][DDDDD][BBBBB][EEEEE][BBBBB]
|
|
|
|
|
|
|
|
Priority values are local to a container, because the priorities of two
|
|
|
|
regions are only compared when they are both children of the same container.
|
|
|
|
This means that the device in charge of the container (typically modelling
|
|
|
|
a bus or a memory controller) can use them to manage the interaction of
|
|
|
|
its child regions without any side effects on other parts of the system.
|
|
|
|
In the example above, the priorities of D and E are unimportant because
|
|
|
|
they do not overlap each other. It is the relative priority of B and C
|
|
|
|
that causes D and E to appear on top of C: D and E's priorities are never
|
|
|
|
compared against the priority of C.
|
|
|
|
|
2011-07-26 13:26:00 +02:00
|
|
|
Visibility
|
|
|
|
----------
|
|
|
|
The memory core uses the following rules to select a memory region when the
|
|
|
|
guest accesses an address:
|
|
|
|
|
|
|
|
- all direct subregions of the root region are matched against the address, in
|
|
|
|
descending priority order
|
|
|
|
- if the address lies outside the region offset/size, the subregion is
|
|
|
|
discarded
|
2013-10-15 16:42:34 +02:00
|
|
|
- if the subregion is a leaf (RAM or MMIO), the search terminates, returning
|
|
|
|
this leaf region
|
2011-07-26 13:26:00 +02:00
|
|
|
- if the subregion is a container, the same algorithm is used within the
|
|
|
|
subregion (after the address is adjusted by the subregion offset)
|
2013-10-15 16:42:34 +02:00
|
|
|
- if the subregion is an alias, the search is continued at the alias target
|
2011-07-26 13:26:00 +02:00
|
|
|
(after the address is adjusted by the subregion offset and alias offset)
|
2013-10-15 16:42:34 +02:00
|
|
|
- if a recursive search within a container or alias subregion does not
|
|
|
|
find a match (because of a "hole" in the container's coverage of its
|
|
|
|
address range), then if this is a container with its own MMIO or RAM
|
|
|
|
backing the search terminates, returning the container itself. Otherwise
|
|
|
|
we continue with the next subregion in priority order
|
|
|
|
- if none of the subregions match the address then the search terminates
|
|
|
|
with no match found
|
2011-07-26 13:26:00 +02:00
|
|
|
|
|
|
|
Example memory map
|
|
|
|
------------------
|
|
|
|
|
|
|
|
system_memory: container@0-2^48-1
|
|
|
|
|
|
|
|
|
+---- lomem: alias@0-0xdfffffff ---> #ram (0-0xdfffffff)
|
|
|
|
|
|
|
|
|
+---- himem: alias@0x100000000-0x11fffffff ---> #ram (0xe0000000-0xffffffff)
|
|
|
|
|
|
2016-03-22 10:45:54 +01:00
|
|
|
+---- vga-window: alias@0xa0000-0xbffff ---> #pci (0xa0000-0xbffff)
|
2011-07-26 13:26:00 +02:00
|
|
|
| (prio 1)
|
|
|
|
|
|
|
|
|
+---- pci-hole: alias@0xe0000000-0xffffffff ---> #pci (0xe0000000-0xffffffff)
|
|
|
|
|
|
|
|
pci (0-2^32-1)
|
|
|
|
|
|
|
|
|
+--- vga-area: container@0xa0000-0xbffff
|
|
|
|
| |
|
|
|
|
| +--- alias@0x00000-0x7fff ---> #vram (0x010000-0x017fff)
|
|
|
|
| |
|
|
|
|
| +--- alias@0x08000-0xffff ---> #vram (0x020000-0x027fff)
|
|
|
|
|
|
|
|
|
+---- vram: ram@0xe1000000-0xe1ffffff
|
|
|
|
|
|
|
|
|
+---- vga-mmio: mmio@0xe2000000-0xe200ffff
|
|
|
|
|
|
|
|
ram: ram@0x00000000-0xffffffff
|
|
|
|
|
2011-12-05 20:54:14 +01:00
|
|
|
This is a (simplified) PC memory map. The 4GB RAM block is mapped into the
|
2011-07-26 13:26:00 +02:00
|
|
|
system address space via two aliases: "lomem" is a 1:1 mapping of the first
|
|
|
|
3.5GB; "himem" maps the last 0.5GB at address 4GB. This leaves 0.5GB for the
|
|
|
|
so-called PCI hole, that allows a 32-bit PCI bus to exist in a system with
|
|
|
|
4GB of memory.
|
|
|
|
|
|
|
|
The memory controller diverts addresses in the range 640K-768K to the PCI
|
2011-08-08 18:58:50 +02:00
|
|
|
address space. This is modelled using the "vga-window" alias, mapped at a
|
2011-07-26 13:26:00 +02:00
|
|
|
higher priority so it obscures the RAM at the same addresses. The vga window
|
|
|
|
can be removed by programming the memory controller; this is modelled by
|
|
|
|
removing the alias and exposing the RAM underneath.
|
|
|
|
|
|
|
|
The pci address space is not a direct child of the system address space, since
|
|
|
|
we only want parts of it to be visible (we accomplish this using aliases).
|
|
|
|
It has two subregions: vga-area models the legacy vga window and is occupied
|
|
|
|
by two 32K memory banks pointing at two sections of the framebuffer.
|
|
|
|
In addition the vram is mapped as a BAR at address e1000000, and an additional
|
|
|
|
BAR containing MMIO registers is mapped after it.
|
|
|
|
|
|
|
|
Note that if the guest maps a BAR outside the PCI hole, it would not be
|
|
|
|
visible as the pci-hole alias clips it to a 0.5GB range.
|
|
|
|
|
|
|
|
MMIO Operations
|
|
|
|
---------------
|
|
|
|
|
|
|
|
MMIO regions are provided with ->read() and ->write() callbacks; in addition
|
|
|
|
various constraints can be supplied to control how these callbacks are called:
|
|
|
|
|
|
|
|
- .valid.min_access_size, .valid.max_access_size define the access sizes
|
|
|
|
(in bytes) which the device accepts; accesses outside this range will
|
|
|
|
have device and bus specific behaviour (ignored, or machine check)
|
2016-02-26 09:40:51 +01:00
|
|
|
- .valid.unaligned specifies that the *device being modelled* supports
|
|
|
|
unaligned accesses; if false, unaligned accesses will invoke the
|
|
|
|
appropriate bus or CPU specific behaviour.
|
2011-07-26 13:26:00 +02:00
|
|
|
- .impl.min_access_size, .impl.max_access_size define the access sizes
|
|
|
|
(in bytes) supported by the *implementation*; other access sizes will be
|
|
|
|
emulated using the ones available. For example a 4-byte write will be
|
2011-12-05 20:54:14 +01:00
|
|
|
emulated using four 1-byte writes, if .impl.max_access_size = 1.
|
2014-05-05 09:53:41 +02:00
|
|
|
- .impl.unaligned specifies that the *implementation* supports unaligned
|
|
|
|
accesses; if false, unaligned accesses will be emulated by two aligned
|
|
|
|
accesses.
|