Update gigapage mappings during remote page faults

Author: fwsGonzo

lib/tinykvm/machine.hpp

@@ -320,6 +320,7 @@ struct Machine
 	void smp_vcpu_broadcast(std::function<void(vCPU&)>);
 	address_t remote_activate_now();
 	void remote_pfault_permanent_ipre(uint64_t return_stack, uint64_t return_address);
+	void remote_update_gigapage_mappings(Machine& other);
 	/* Prepare for resume with a pagetable reload */
 	void prepare_vmresume(address_t fsbase = 0, bool reload_pagetables = true);
 

lib/tinykvm/remote.cpp

@@ -30,6 +30,33 @@ void Machine::permanent_remote_connect(Machine& other)
 	other.remote_connect(*this, true);
 }
 
+void Machine::remote_update_gigapage_mappings(Machine& remote)
+{
+	auto& caller = *this;
+	const auto remote_vmem = remote.main_memory().vmem();
+	static constexpr uint64_t PDE64_ADDR_MASK = ~0x8000000000000FFF;
+	auto* main_pml4 = caller.main_memory().page_at(caller.main_memory().page_tables);
+	auto* main_pdpt = caller.main_memory().page_at(main_pml4[0] & PDE64_ADDR_MASK);
+
+	auto* remote_pml4 = remote.main_memory().page_at(remote.main_memory().page_tables);
+	auto* remote_pdpt = remote.main_memory().page_at(remote_pml4[0] & PDE64_ADDR_MASK);
+
+	// Gigabyte starting index and end index (rounded up)
+	const auto begin = remote_vmem.physbase >> 30;
+	const auto end   = (remote_vmem.remote_end + 0x3FFFFFFF) >> 30;
+
+	for (size_t i = begin; i < end; i++)
+	{
+		if (main_pdpt[i] != remote_pdpt[i]) {
+			if constexpr (VERBOSE_REMOTE) {
+				fprintf(stderr, "Updating remote PDPT entry %zu from 0x%lX to 0x%lX\n",
+					i, main_pdpt[i], remote_pdpt[i]);
+			}
+			main_pdpt[i] = remote_pdpt[i];
+		}
+	}
+
+}
 void Machine::remote_connect(Machine& remote, bool connect_now)
 {
 	const auto remote_vmem = remote.main_memory().vmem();
@@ -50,25 +77,7 @@ void Machine::remote_connect(Machine& remote, bool connect_now)
 	if (connect_now)
 	{
 		// Copy gigabyte entries covered by remote memory into these page tables
-		static constexpr uint64_t PDE64_ADDR_MASK = ~0x8000000000000FFF;
-		auto* main_pml4 = this->main_memory().page_at(this->main_memory().page_tables);
-		auto* main_pdpt = this->main_memory().page_at(main_pml4[0] & PDE64_ADDR_MASK);
-
-		auto* remote_pml4 = remote.main_memory().page_at(remote.main_memory().page_tables);
-		auto* remote_pdpt = remote.main_memory().page_at(remote_pml4[0] & PDE64_ADDR_MASK);
-
-		// Gigabyte starting index and end index (rounded up)
-		const auto begin = remote_vmem.physbase >> 30;
-		const auto end   = (remote_vmem.remote_end + 0x3FFFFFFF) >> 30;
-		if (UNLIKELY(begin >= 512 || end > 512 || begin >= end))
-			throw MachineException("Remote memory produced invalid indexes (>512GB?)");
-
-		// Install gigabyte entries from remote VM into this VM
-		// The VM and page tables technically support 2MB region alignments.
-		for (size_t i = begin; i < end; i++)
-		{
-			main_pdpt[i] = remote_pdpt[i]; // GB-page
-		}
+		this->remote_update_gigapage_mappings(remote);
 	}
 
 	// Finalize
@@ -118,7 +127,7 @@ void Machine::ipre_remote_resume_now(bool save_all, std::function<void(Machine&)
 
 	const auto remote_cow_counter = remote().memory.cow_written_pages.size();
 	bool do_prepare = false;
-	if (this->m_remote_cow_counter != remote_cow_counter) {
+	if (true || this->m_remote_cow_counter != remote_cow_counter) {
 		this->m_remote_cow_counter = remote_cow_counter;
 		// New working memory pages have been created in the remote,
 		// so we need to make sure we see the latest changes.

lib/tinykvm/vcpu_run.cpp

@@ -332,6 +332,11 @@ long vCPU::run_once()
 				WritablePageOptions zero_opts;
 				zero_opts.zeroes = false;
 				auto result = writable_page_at(memory, addr, PDE64_USER | PDE64_RW, zero_opts);
+				if (machine().has_remote() && machine().remote().is_foreign_address(addr) && machine().remote().is_remote_connected()) {
+					// If a new gigapage was created, we need to update the
+					// PML4[0] 512GB page table entry in the caller VM too
+					machine().remote().remote_update_gigapage_mappings(machine());
+				}
 				if constexpr (false) {
 					char buffer[256];
 					PRINTER(machine().m_printer, buffer,
@@ -341,6 +346,22 @@ long vCPU::run_once()
 					PRINTER(machine().m_printer, buffer,
 						"  Our bank arena: begin=0x%lX\n",
 						memory.banks.arena_begin());
+					static uint64_t last_reported = 0;
+					static int count = 0;
+					if (last_reported == addr) {
+						count++;
+						PRINTER(machine().m_printer, buffer,
+							"  Page fault repeats %d times, address=0x%lX\n",
+							count, last_reported);
+						if (count > 2) {
+							//this->handle_exception(intr);
+							print_pagetables(memory);
+							Machine::machine_exception("Too many page faults", intr);
+						}
+					} else {
+						last_reported = addr;
+						count = 0;
+					}
 				}
 				return KVM_EXIT_IO;
 			}