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| -rw-r--r-- | docs/devel/memory.rst (renamed from docs/devel/memory.txt) | 132 |
1 files changed, 72 insertions, 60 deletions
diff --git a/docs/devel/memory.txt b/docs/devel/memory.rst index 42577e1d86..b6a4c37ea5 100644 --- a/docs/devel/memory.txt +++ b/docs/devel/memory.rst @@ -1,19 +1,20 @@ +============== 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 - to different destinations +- ordinary RAM +- memory-mapped I/O (MMIO) +- memory controllers that can dynamically reroute physical memory regions + to different destinations The memory model provides support for - - tracking RAM changes by the guest - - setting up coalesced memory for kvm - - setting up ioeventfd regions for kvm +- tracking RAM changes by the guest +- setting up coalesced memory for kvm +- setting up ioeventfd regions for kvm Memory is modelled as an acyclic graph of MemoryRegion objects. Sinks (leaves) are RAM and MMIO regions, while other nodes represent @@ -98,25 +99,30 @@ 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() + +- 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() + +- 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() + +- 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. @@ -218,7 +224,7 @@ For example, suppose we have a container A of size 0x8000 with two subregions 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 of its own subregions: D of size 0x1000 at offset 0 and E of size 0x1000 at -offset 0x2000. As a diagram: +offset 0x2000. As a diagram:: 0 1000 2000 3000 4000 5000 6000 7000 8000 |------|------|------|------|------|------|------|------| @@ -228,8 +234,9 @@ offset 0x2000. As a diagram: D: [DDDDD] E: [EEEEE] -The regions that will be seen within this address range then are: - [CCCCCCCCCCCC][DDDDD][CCCCC][EEEEE][CCCCC] +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 @@ -237,8 +244,9 @@ 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] +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. @@ -257,6 +265,7 @@ 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 - if the subregion is a leaf (RAM or MMIO), the search terminates, returning @@ -270,36 +279,39 @@ guest accesses an address: 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 Example memory map ------------------ -system_memory: container@0-2^48-1 - | - +---- lomem: alias@0-0xdfffffff ---> #ram (0-0xdfffffff) - | - +---- himem: alias@0x100000000-0x11fffffff ---> #ram (0xe0000000-0xffffffff) - | - +---- vga-window: alias@0xa0000-0xbffff ---> #pci (0xa0000-0xbffff) - | (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 +:: + + system_memory: container@0-2^48-1 + | + +---- lomem: alias@0-0xdfffffff ---> #ram (0-0xdfffffff) + | + +---- himem: alias@0x100000000-0x11fffffff ---> #ram (0xe0000000-0xffffffff) + | + +---- vga-window: alias@0xa0000-0xbffff ---> #pci (0xa0000-0xbffff) + | (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 This is a (simplified) PC memory map. The 4GB RAM block is mapped into the system address space via two aliases: "lomem" is a 1:1 mapping of the first @@ -336,16 +348,16 @@ rather than completing successfully; those devices can use the 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) - - .valid.unaligned specifies that the *device being modelled* supports - unaligned accesses; if false, unaligned accesses will invoke the - appropriate bus or CPU specific behaviour. - - .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 - emulated using four 1-byte writes, if .impl.max_access_size = 1. - - .impl.unaligned specifies that the *implementation* supports unaligned - accesses; if false, unaligned accesses will be emulated by two aligned - accesses. +- .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) +- .valid.unaligned specifies that the *device being modelled* supports + unaligned accesses; if false, unaligned accesses will invoke the + appropriate bus or CPU specific behaviour. +- .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 + emulated using four 1-byte writes, if .impl.max_access_size = 1. +- .impl.unaligned specifies that the *implementation* supports unaligned + accesses; if false, unaligned accesses will be emulated by two aligned + accesses. |