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);
}
