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Redesign frame allocation for easier formal verification (#1004)
* A single type `Frames` is now used to represent all physical memory frames. * Each `Frames` object is globally unique, and ownership of one represents the exclusive capability to access those frames, e.g., map pages to them. * The `Frames` struct is parameterized with a const generic enum that determines which state it is in, one of four `memory_structs::MemoryState`s: 1. Free: the range of frames is free and is owned by the frame allocator. * `Frames<{MemoryState::Free}>` is type aliased to `FreeFrames`. 2. Allocated: the range of frames has been allocated, and is owned by another entity outside of the frame allocator. * `Frames<{MemoryState::Allocated}>` is type aliased to `AllocatedFrames`, which replaces the previous struct of the same name. 3. Mapped: the range of frames has been mapped by a range of virtual pages. * `Frames<{MemoryState::Mapped}>` is type aliased to `MappedFrames`, which is not yet used in the Theseus codebase. 4. Unmapped: the range of frames has just been unmapped by a range of virtual pages, but has yet to be returned to the frame allocator. * `Frames<{MemoryState::Unmapped}>` is type aliased to `UnmappedFrames`, which is used as an intermediary step before transitioning back into `AllocatedFrames`. * See the documentation of `Frames` for more info on state transitions: (Free) <---> (Allocated) --> (Mapped) --> (Unmapped) --> (Allocated) <---> (Free) * `FreeFrames` is used in favor of `Chunk`. Note that the term "chunk" still appears in the code in order to minimize the sheer volume of tiny changes. * Added a few new APIs to frame-related types, mostly for convenience: `split_at`, `split_range`, `contains_range`. * Combined the `PhysicalMemoryRegion` and `Region` into a single type used across the entire frame allocator. * The core logic of the frame allocator has been changed to accommodate the new `Frames` type, which is a verified "true linear" type that cannot be cloned or have its inner fields mutated. * The entire point of this redesigns is to make the frame allocator amenable to formal verification based on typestate analysis combined with Prusti-verifiable pre- and post-conditions for key functions. * Actual verification code and proofs of frame allocation correctness are coming soon in future PRs. Co-authored-by: Kevin Boos <kevinaboos@gmail.com> 0dd9dc6
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<!DOCTYPE html><html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><meta name="generator" content="rustdoc"><meta name="description" content="List of all items in this crate"><title>List of all items in this crate</title><link rel="preload" as="font" type="font/woff2" crossorigin href="../static.files/SourceSerif4-Regular-46f98efaafac5295.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../static.files/FiraSans-Regular-018c141bf0843ffd.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../static.files/FiraSans-Medium-8f9a781e4970d388.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../static.files/SourceCodePro-Regular-562dcc5011b6de7d.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../static.files/SourceSerif4-Bold-a2c9cd1067f8b328.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin 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href="../frame_allocator/index.html"><img class="rust-logo" src="../static.files/rust-logo-151179464ae7ed46.svg" alt="logo"></a><h2 class="location"><a href="#">Crate frame_allocator</a></h2><div class="sidebar-elems"><section><ul class="block"><li><a href="#structs">Structs</a></li><li><a href="#enums">Enums</a></li><li><a href="#functions">Functions</a></li></ul></section></div></nav><main><div class="width-limiter"><nav class="sub"><form class="search-form"><span></span><input class="search-input" name="search" aria-label="Run search in the documentation" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"><div id="help-button" title="help" tabindex="-1"><a href="../help.html">?</a></div><div id="settings-menu" tabindex="-1"><a href="../settings.html" title="settings"><img width="22" height="22" alt="Change settings" src="../static.files/wheel-7b819b6101059cd0.svg"></a></div></form></nav><section id="main-content" class="content"><h1>List of all items</h1><h3 id="structs">Structs</h3><ul class="all-items"><li><a href="struct.AllocatedFrame.html">AllocatedFrame</a></li><li><a href="struct.AllocatedFrames.html">AllocatedFrames</a></li><li><a href="struct.AllocatedFramesIter.html">AllocatedFramesIter</a></li><li><a href="struct.DeferredAllocAction.html">DeferredAllocAction</a></li><li><a href="struct.PhysicalMemoryRegion.html">PhysicalMemoryRegion</a></li></ul><h3 id="enums">Enums</h3><ul class="all-items"><li><a href="enum.MemoryRegionType.html">MemoryRegionType</a></li></ul><h3 id="functions">Functions</h3><ul class="all-items"><li><a href="fn.allocate_frames.html">allocate_frames</a></li><li><a href="fn.allocate_frames_at.html">allocate_frames_at</a></li><li><a href="fn.allocate_frames_by_bytes.html">allocate_frames_by_bytes</a></li><li><a href="fn.allocate_frames_by_bytes_at.html">allocate_frames_by_bytes_at</a></li><li><a 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src="../static.files/wheel-7b819b6101059cd0.svg"></a></div></form></nav><section id="main-content" class="content"><h1>List of all items</h1><h3 id="structs">Structs</h3><ul class="all-items"><li><a href="struct.AllocatedFrame.html">AllocatedFrame</a></li><li><a href="struct.AllocatedFramesIter.html">AllocatedFramesIter</a></li><li><a href="struct.DeferredAllocAction.html">DeferredAllocAction</a></li><li><a href="struct.Frames.html">Frames</a></li><li><a href="struct.PhysicalMemoryRegion.html">PhysicalMemoryRegion</a></li><li><a href="struct.SplitFrames.html">SplitFrames</a></li></ul><h3 id="enums">Enums</h3><ul class="all-items"><li><a href="enum.MemoryRegionType.html">MemoryRegionType</a></li></ul><h3 id="functions">Functions</h3><ul class="all-items"><li><a href="fn.allocate_frames.html">allocate_frames</a></li><li><a href="fn.allocate_frames_at.html">allocate_frames_at</a></li><li><a href="fn.allocate_frames_by_bytes.html">allocate_frames_by_bytes</a></li><li><a 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