Add dump-state command to write WinDbg-compatible .vmrs dump files

[jstarks]

This adds the ability to dump a running VM's processor state and memory to a .vmrs file that can be opened with WinDbg via VmSavedStateDumpProvider.dll. This is useful for offline debugging of guest crashes without needing a live debugger attached.

The implementation is split across three layers:

hvs_file is a new standalone crate that implements the HyperV Storage binary key-value file format used by .vmrs, .vmcx, and .vsv files. It provides both a reader and writer, with no VMM dependencies. The format is documented in FORMAT.md.

hyperv_dump builds on hvs_file to assemble complete .vmrs dump files. It constructs the hypervisor save/restore chunk stream from virt register types then wraps it with memory block metadata and streams guest RAM through a caller-provided GuestMemoryReader trait. Tests validate that this crate produces files that are compatible with the Hyper-V dump provider DLL.

vmm_core / openvmm integration exposes dump generation through VmRpc::DumpState and a dump-state REPL command. The partition unit stops VPs and builds the partition state blob; the worker streams guest memory to disk. The hyperv_dump dependency in vmm_core is gated behind a dump cargo feature, enabled for OpenVMM but not OpenHCL.

New hypervisor save/restore chunk definitions are added to hvdef::save_restore for the on-disk structures (chunk headers, register chunks for x64 and ARM64, VTL markers, etc.).

[Copilot]

Pull request overview

Copilot reviewed 25 out of 26 changed files in this pull request and generated 5 comments.

[Copilot]

Pull request overview

Copilot reviewed 26 out of 27 changed files in this pull request and generated 8 comments.

Comments suppressed due to low confidence (2)

vmm_core/hyperv_dump/src/vmrs_writer.rs:116

• RamBlock* values are written with block_len = min(1MiB, remaining), so the final block of a range can be < 1MiB. Per support/hvs_file/FORMAT.md, sizes < 1MiB are interpreted as XPRESS-compressed, so emitting a short uncompressed tail block will likely be misread by consumers. Consider always writing exactly 1 MiB per RamBlock (zero-fill the remainder when remaining < 1MiB) or implement XPRESS compression for short blocks.

            while gpa < gpa_end {
                let block_len = DATA_BLOCK_SIZE.min((gpa_end - gpa) as usize);
                let buf = &mut block_buf[..block_len];
                reader.read_gpa(gpa, buf)?;

                key_buf.clear();
                write!(key_buf, "/savedstate/RamBlock{data_block_idx}").unwrap();
                self.hvs.add_array(&key_buf, buf)?;
                data_block_idx += 1;

vmm_core/hyperv_dump/src/vmrs_writer.rs:90

• finish() can produce a .vmrs with zero RamMemoryBlock* entries when no memory ranges are added. The format doc in this PR (support/hvs_file/FORMAT.md) states /savedstate/RamMemoryBlock0 is a minimum required key for the dump provider to open the file. Either enforce at least one memory range (return InvalidInput) or write the required minimal memory metadata so the writer can’t generate an unloadable file.

    /// Writes the complete `.vmrs` file, reading guest memory on demand.
    ///
    /// `partition_state` is the blob from [`crate::PartitionStateBuilder::finish`].
    /// Memory is streamed through a reusable 1 MiB buffer — at no point
    /// is the entire guest address space materialized in memory.
    pub fn finish(
        mut self,
        partition_state: &[u8],
        reader: &mut dyn GuestMemoryReader,
    ) -> io::Result<W> {
        // VM version
        self.hvs.add_int("/savedstate/VmVersion", VM_VERSION);
        self.hvs
            .add_int("/configuration/properties/version", VM_VERSION);

        // Partition state
        self.hvs
            .add_array("/savedstate/savedVM/partition_state", partition_state)?;

        // Memory layout: split ranges into 1 MiB blocks, streaming each
        // block through a reusable buffer.
        let mut data_block_idx = 0u64;
        let mut block_buf = vec![0u8; DATA_BLOCK_SIZE];
        let mut key_buf = String::new();

        for (i, range) in self.ranges.iter().enumerate() {

[Copilot]

Pull request overview

Copilot reviewed 28 out of 29 changed files in this pull request and generated 6 comments.

[github-actions]

3 Petri tests failed (3 unstable)

[Copilot]

Pull request overview

Copilot reviewed 28 out of 29 changed files in this pull request and generated 7 comments.