# FlatView FlatView，从字面上看意思就是 扁平视图。那是谁的偏平视图呢？ 从大了说是地址空间的偏平视图，但是仔细想想它是对应MemoryRegion的。因为MemoryRegion是一颗树，那相应的就可以有一个偏平空间。 说到这儿，其实已经没有什么花头了。不就是一个偏平视图么？但是为了充数，还是要展开讲讲的。突然想到了《三体》世界中的低纬展开，这个MemoryRegion到FlatView的过程还真有点像。 这个过程在qemu中分成了两步： * generate\_memory\_topology() * address\_space\_set\_flatview() 后者是将AddressSpace和FlatView进行关联。 而前者的工作又分成两部分： * render\_memory\_region * flatview\_add\_to\_dispatch ## render\_memory\_region 这个函数的作用就是将树状的MemoryRegion展开成一维的FlatView。 因为确实没啥多说的，还是用张图来表示AddressSpace，MemoryRegion和FlatView之间的关系。 ``` AddressSpace +-------------------------+ |name | | (char *) | FlatView (An array of FlatRange) +-------------------------+ +----------------------+ |current_map | -------->|nr | | (FlatView *) | |nr_allocated | +-------------------------+ | (unsigned) | FlatRange FlatRange | | +----------------------+ | | |ranges | ------> +---------------------+---------------------+ | | | (FlatRange *) | |offset_in_region |offset_in_region | | | +----------------------+ | (hwaddr) | (hwaddr) | | | +---------------------+---------------------+ | | |addr(AddrRange) |addr(AddrRange) | | | | +----------------| +----------------+ | | | |start (Int128) | |start (Int128) | | | | |size (Int128) | |size (Int128) | | | +----+----------------+----+----------------+ | | |mr |mr | | | | (MemoryRegion *) | (MemoryRegion *) | | | +---------------------+---------------------+ | | | | | | | | MemoryRegion(system_memory/system_io) +-------------------------+ +----------------------+ |root | | | root of a MemoryRegion | (MemoryRegion *) | -------->| | tree +-------------------------+ +----------------------+ ``` 在AddressSpace中，root和current\_map分别指向了树状的地址空间和对应的一维展开。 至于为什么要使用这样两种数据结构，暂时还不知道这样做的好处。等我想明白了再回来解释。 ## flatview\_add\_to\_dispatch 这个函数的主要任务就是构建AddressSpaceDispatch这个结构了。让人吃惊的是，这是一个庞然大物。 恐怕大家是要缩小了才能看清楚的吧。 ``` AddressSpaceDispatch +-------------------------+ |as | | (AddressSpace *) | +-------------------------+ |mru_section | | (MemoryRegionSection*)| | | | | | | | | | | +-------------------------+ |map(PhysPageMap) | MemoryRegionSection[] | +---------------------+ +---------------------------+---------------------------+---------------------------+---------------------------+---------------------------+---------------------------+ | |sections |-------->|mr = io_mem_unassigned |mr = io_mem_notdirty |mr = io_mem_rom |mr = io_mem_watch |mr = one mr in tree |mr = subpage_t->iomem | | | MemoryRegionSection*| | (MemoryRegion *) | (MemoryRegion *) | (MemoryRegion *) | (MemoryRegion *) | (MemoryRegion *) | (MemoryRegion *) | | | | | | | | | | | | +---------------------+ +---------------------------+---------------------------+---------------------------+---------------------------+---------------------------+---------------------------+ | |sections_nb | |fv |fv |fv |fv |fv |fv | | |sections_nb_alloc | | (FlatView *) | (FlatView *) | (FlatView *) | (FlatView *) | (FlatView *) | (FlatView *) | | | (unsigned) | +---------------------------+---------------------------+---------------------------+---------------------------+---------------------------+---------------------------+ | +---------------------+ |size (Int128) |size (Int128) |size (Int128) |size (Int128) |size (Int128) |size (Int128) | | | | +---------------------------+---------------------------+---------------------------+---------------------------+---------------------------+---------------------------+ | | | |offset_within_region |offset_within_region |offset_within_region |offset_within_region |offset_within_region |offset_within_region | | | | | (hwaddr) | (hwaddr) | (hwaddr) | (hwaddr) | (hwaddr) | (hwaddr) | | | | |offset_within_address_space|offset_within_address_space|offset_within_address_space|offset_within_address_space|offset_within_address_space|offset_within_address_space| | | | | (hwaddr) GPA | (hwaddr) GPA | (hwaddr) GPA | (hwaddr) GPA | (hwaddr) | (hwaddr) | | | | +---------------------------+---------------------------+---------------------------+---------------------------+---------------------------+---------------------------+ | | | ^ | | | nodes[1] | | | | +---->+------------------+ | | | | | |u32 skip:6 | = 0 | | | | | |u32 ptr:26 | = 4 -----------------------------------------+ | | | P_L2_LEVELS = 6 | +------------------+ | | | nodes[0] = PhysPageEntry[P_L2_SIZE = 2^9] | | | | +---------------------+ +------------------+ | | ... | | |nodes | ------->|u32 skip:6 | = 1 | | | | | (Node *) | |u32 ptr:26 | = 1 -------------+ +------------------+ | +---------------------+ +------------------+ |u32 skip:6 | = 0 | |nodes_nb | | | |u32 ptr:26 | = PHYS_SECTION_UNASSIGNED | |nodes_nb_alloc | | ... | +------------------+ | | (unsigned) | | | | +---------------------+ +------------------+ | | | |u32 skip:6 | = 1 | | | |u32 ptr:26 | = PHYS_MAP_NODE_NIL nodes[2] | | | +------------------+ +---->+------------------+ | | | |u32 skip:6 | = 1 | |u32 skip:6 | | | | |u32 ptr:26 | = 2 -------------+ |u32 ptr:26 | | | | +------------------+ +------------------+ | | | ^ | | | | | | | ... | | | | | | | +---+---------------------+ | +------------------+ |phys_map(PhysPageEntry) | | |u32 skip:6 | | +---------------------+ | |u32 ptr:26 | | |u32 skip:6 | = 1 | +------------------+ | |u32 ptr:26 | = 0 --------+ +---+---------------------+ ``` 简单来说 * phys\_map 像是CR3 * nodes 是一个用链表存储了的页表 * sections 是nodes的叶子ptr指向的内容，其中包含了MemoryRegion 希望这么解释能够在一定程度上帮助理解。 --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. 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