static void read_guest_memory(struct lg_cpu *cpu) { int i; struct file *memory; memory = file_open("/tmp/lgmemory", O_RDWR, 0644); for (i = 0; i < cpu->lg->pfn_limit; i++) { file_read(memory, i * PAGE_SIZE, page_buffer, PAGE_SIZE); __lgwrite(cpu, i * PAGE_SIZE, page_buffer, PAGE_SIZE); } file_close(memory); }
/* * Our hypercalls mechanism used to be based on direct software interrupts. * After Anthony's "Refactor hypercall infrastructure" kvm patch, we decided to * change over to using kvm hypercalls. * * KVM_HYPERCALL is actually a "vmcall" instruction, which generates an invalid * opcode fault (fault 6) on non-VT cpus, so the easiest solution seemed to be * an *emulation approach*: if the fault was really produced by an hypercall * (is_hypercall() does exactly this check), we can just call the corresponding * hypercall host implementation function. * * But these invalid opcode faults are notably slower than software interrupts. * So we implemented the *patching (or rewriting) approach*: every time we hit * the KVM_HYPERCALL opcode in Guest code, we patch it to the old "int 0x1f" * opcode, so next time the Guest calls this hypercall it will use the * faster trap mechanism. * * Matias even benchmarked it to convince you: this shows the average cycle * cost of a hypercall. For each alternative solution mentioned above we've * made 5 runs of the benchmark: * * 1) direct software interrupt: 2915, 2789, 2764, 2721, 2898 * 2) emulation technique: 3410, 3681, 3466, 3392, 3780 * 3) patching (rewrite) technique: 2977, 2975, 2891, 2637, 2884 * * One two-line function is worth a 20% hypercall speed boost! */ static void rewrite_hypercall(struct lg_cpu *cpu) { /* * This are the opcodes we use to patch the Guest. The opcode for "int * $0x1f" is "0xcd 0x1f" but vmcall instruction is 3 bytes long, so we * complete the sequence with a NOP (0x90). */ u8 insn[3] = {0xcd, 0x1f, 0x90}; __lgwrite(cpu, guest_pa(cpu, cpu->regs->eip), insn, sizeof(insn)); /* * The above write might have caused a copy of that page to be made * (if it was read-only). We need to make sure the Guest has * up-to-date pagetables. As this doesn't happen often, we can just * drop them all. */ guest_pagetable_clear_all(cpu); }