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Diffstat (limited to 'docs/memory.txt')
| -rw-r--r-- | docs/memory.txt | 26 |
1 files changed, 25 insertions, 1 deletions
diff --git a/docs/memory.txt b/docs/memory.txt index 2ceb348942..8745f7603f 100644 --- a/docs/memory.txt +++ b/docs/memory.txt @@ -26,14 +26,28 @@ These represent memory as seen from the CPU or a device's viewpoint. Types of regions ---------------- -There are four types of memory regions (all represented by a single C type +There are multiple types of memory regions (all represented by a single C type MemoryRegion): - RAM: a RAM region is simply a range of host memory that can be made available to the guest. + 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(). - 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. + You initialize these with memory_region_io(), passing it a MemoryRegionOps + structure describing the callbacks. + +- ROM: a ROM 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(). + +- 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(). - container: a container simply includes other memory regions, each at a different offset. Containers are useful for grouping several regions @@ -45,12 +59,22 @@ MemoryRegion): can overlay a subregion of RAM with MMIO or ROM, or a PCI controller that does not prevent card from claiming overlapping BARs. + You initialize a pure container with memory_region_init(). + - 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. + 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 + handled by the host kernel when KVM is enabled. + You initialize these with memory_region_init_reservation(), or by + passing a NULL callback parameter to memory_region_init_io(). 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 |