Merge pull request #58 from lrowe/fix-accessed-pages

Open existing snapshot file readonly and include size of accessed pages

Author: fwsGonzo

lib/tinykvm/amd64/paging.cpp

@@ -531,13 +531,13 @@ void foreach_page_makecow(vMemory& mem, uint64_t kernel_end, uint64_t shared_mem
 		entry &= ~PDE64_ACCESSED;
 	});
 }
-std::vector<uint64_t> get_accessed_pages(const vMemory& memory)
+std::vector<std::pair<uint64_t, uint64_t>> get_accessed_pages(const vMemory& memory)
 {
-	std::vector<uint64_t> accessed_pages;
+	std::vector<std::pair<uint64_t, uint64_t>> accessed_pages;
 	foreach_page(memory,
-	[&accessed_pages] (uint64_t addr, uint64_t& entry, size_t /*size*/) {
-		if ((entry & (PDE64_ACCESSED | PDE64_PRESENT)) == (PDE64_ACCESSED | PDE64_PRESENT)) {
-			accessed_pages.push_back(addr & PDE64_ADDR_MASK);
+	[&accessed_pages] (uint64_t addr, uint64_t& entry, size_t size) {
+		if ((entry & (PDE64_PS | PDE64_ACCESSED | PDE64_PRESENT)) == (PDE64_PS | PDE64_ACCESSED | PDE64_PRESENT)) {
+			accessed_pages.push_back({addr & PDE64_ADDR_MASK, size});
 		}
 	}, false);
 	return accessed_pages;

lib/tinykvm/amd64/paging.hpp

@@ -14,7 +14,7 @@ using foreach_page_t = std::function<void(uint64_t, uint64_t&, size_t)>;
 extern void foreach_page(vMemory&, foreach_page_t callback, bool skip_oob_addresses = true);
 extern void foreach_page(const vMemory&, foreach_page_t callback, bool skip_oob_addresses = true);
 extern void foreach_page_makecow(vMemory&, uint64_t kernel_end, uint64_t shared_memory_boundary);
-extern std::vector<uint64_t> get_accessed_pages(const vMemory& memory);
+extern std::vector<std::pair<uint64_t, uint64_t>> get_accessed_pages(const vMemory& memory);
 
 extern void page_at(vMemory&, uint64_t addr, foreach_page_t, bool ignore_missing = false);
 struct WritablePage {

lib/tinykvm/machine.hpp

@@ -245,7 +245,7 @@ struct Machine
 	void set_main_memory_writable(bool v) { memory.main_memory_writes = v; }
 	bool is_forked() const noexcept { return m_forked; }
 	bool uses_cow_memory() const noexcept { return m_forked || m_prepped; }
-	std::vector<uint64_t> get_accessed_pages() const;
+	std::vector<std::pair<uint64_t, uint64_t>> get_accessed_pages() const;
 
 	/* Remote VM through address space merging */
 	void remote_connect(Machine& other, bool connect_now = false);
@@ -299,7 +299,7 @@ struct Machine
 	/* Store non-memory VM state to the already existing cold
 	   start state area in memory. Any failure will throw an
 	   exception. The memory must have been pre-allocated. */
-	void save_snapshot_state_now(const std::vector<uint64_t>& populate_pages = {}) const;
+	void save_snapshot_state_now(const std::vector<std::pair<uint64_t, uint64_t>>& populate_pages = {}) const;
 	/* Check if the VM was loaded from a snapshot state. */
 	bool has_snapshot_state() const noexcept { return m_loaded_from_snapshot; }
 	/* Get pointer to user area in snapshot state memory, or nullptr

lib/tinykvm/machine_state.cpp

@@ -208,7 +208,7 @@ bool Machine::load_snapshot_state()
 	}
 	return true;
 }
-void Machine::save_snapshot_state_now(const std::vector<uint64_t>& populate_pages) const
+void Machine::save_snapshot_state_now(const std::vector<std::pair<uint64_t, uint64_t>>& populate_pages) const
 {
 	if (this->is_forked()) {
 		throw std::runtime_error("Cannot save snapshot state of a forked VM");
@@ -242,12 +242,12 @@ void Machine::save_snapshot_state_now(const std::vector<uint64_t>& populate_page
 		if (!populate_pages.empty()) {
 			uint64_t current_begin = 0;
 			uint64_t current_end = 0;
-			for (uint64_t page_addr : populate_pages) {
+			for (const auto& [page_addr, size] : populate_pages) {
 				if (page_addr >= MemoryBanks::ARENA_BASE_ADDRESS || page_addr < kernel_end_address())
 					continue;
 				// Merge contiguous ranges
 				if (current_end == page_addr) {
-					current_end += vMemory::PageSize();
+					current_end += size;
 					continue;
 				}
 				// Store previous range
@@ -259,7 +259,7 @@ void Machine::save_snapshot_state_now(const std::vector<uint64_t>& populate_page
 				}
 				// Start new range
 				current_begin = page_addr;
-				current_end = page_addr;
+				current_end = page_addr + size;
 			}
 			// Store last range
 			if (current_end != current_begin) {

lib/tinykvm/memory.cpp

@@ -397,9 +397,15 @@ vMemory::AllocationResult
 	if (filename.empty()) {
 		throw std::runtime_error("No VM snapshot file specified");
 	}
-	const int fd = open(filename.c_str(), O_RDWR | O_CREAT | O_CLOEXEC, 0600);
+	int fd = open(filename.c_str(), O_RDONLY | O_CLOEXEC);
 	if (fd < 0) {
-		throw std::runtime_error("Failed to open VM snapshot file: " + filename);
+		if (errno != ENOENT) {
+			throw std::runtime_error("Failed to open VM snapshot file: " + filename);
+		}
+		fd = open(filename.c_str(), O_RDWR | O_CREAT | O_CLOEXEC, 0600);
+		if (fd < 0) {
+			throw std::runtime_error("Failed to create VM snapshot file: " + filename);
+		}
 	}
 	struct stat st;
 	if (fstat(fd, &st) != 0) {
@@ -512,7 +518,7 @@ char* vMemory::get_userpage_at(uint64_t addr) const
 #endif
 }
 
-std::vector<uint64_t> Machine::get_accessed_pages() const
+std::vector<std::pair<uint64_t, uint64_t>> Machine::get_accessed_pages() const
 {
 	return tinykvm::get_accessed_pages(this->main_memory());
 }