KVM run and exit

• http://blog.csdn.net/dashulu/article/details/17090293

Qemu run vcpu:

kvm_cpu_exec()

- kvm_vcpu_ioctl(cpu, KVM_RUN, 0)
- switch (run->exit_reason) ...

KVM_RUN vcpu_ioctl:

[x86]

   kvm_vcpu_ioctl()
=> kvm_arch_vcpu_ioctl_run() // x86 version
=> vcpu_run()                // infinite loop for VM
=> vcpu_enter_guest()

   - kvm_x86_op->run() = vmx_vcpu_run()

     - run guest OS. // inline asm, VMLAUNCH
     - vmx->exit_reason = vmcs_read32(VM_EXIT_REASON);

   - kvm_x86_op->handle_exit() = vmx_handle_exit()

     - kvm_vmx_exit_handlers[vmx->exit_reason]

[arm64]

   kvm_vcpu_ioctl()
=> kvm_arch_vcpu_ioctl_run()

   [1] ret = kvm_call_hyp(__kvm_vcpu_run, vcpu);

       [ ] kvm_call_hyp == __kvm_call_hyp // kvm_call_hyp at ``arch/arm64/include/asm/kvm_host.h``
       [ ] __kvm_vcpu_run == __guest_run
       [2] __guest_run() // at ``arch/arm64/kvm/hyp/switch.c``

           [3] vcpu = kern_hyp_va(vcpu);
           [3] host_ctxt = kern_hyp_va(vcpu->arch.host_cpu_context);
           [3] again: exit_code = __guest_enter(vcpu, host_ctxt); // at ``arch/arm64/kvm/hyp/entry.S``

               [4] run guest OS by exception return instruction (ERET) // PC = ELR_hyp, CPSR = SPSR_hyp

           [3] if (exit_code == ARM_EXCEPTION_TRAP && !__populate_fault_info(vcpu)) goto again

   [1] handle_exit() // arm64/kvm/handle_exit.c , arm/kvm/handle_exit.c

       [2] arm_exit_handlers[]

---

• QEMU / KVM interface

  • enter: kvm_vcpu_ioctl(KVM_RUN)

  • exit: ioctl syscall return, struct kvm_run (shared memory, mmap vcpu_fd)

    • struct kvm_run: Documentation/virtual/kvm/api.txt ch5 The kvm_run structure

    • QEMU use kvm_run->exit_reason to do device emulation and … etc. (kvm_cpu_exec)

    • shared memory, mmap vcpu_fd: env->kvm_run = mmap(NULL, mmap_size, PROT_READ | PROT_WRITE, MAP_SHARED, env->kvm_fd, 0); at kvm_init_vcpu()

• KVM / Guest interface

  • [x86] enter: vmlaunch instruction

  • [x86] exit: vmexit, VMCS exit_reason field

  • [arm64] enter: ERET or ?? instruction

  • [arm64] exit: HSR register

---

MMIO:

-  arm_exit_handlers[ESR_ELx_EC_IABT_LOW, ESR_ELx_EC_DABT_LOW] = kvm_handle_guest_abort()
=> kvm_handle_guest_abort() // at ``arch/arm/mmu.c``

   - io_mem_abort()         // at ``arch/arm/mmio.c``

     - kvm_io_bus_write() (or read)                // at ``virt/kvm/kvm_main.c``
     - kvm_handle_mmio_return()
     - run->exit_reason = KVM_EXIT_MMIO; return 0; // handled in userland, QEMU emulation

   - user_mem_abort()       // at ``arch/arm/mmu.c``

MMIO2

• kvm_io_bus_write() // at virt/kvm/kvm_main.c

  • kvm_iodevice_write()

IO device and bus

• struct kvm_io_device at include/kvm/iodev.h

  • struct kvm_io_device_op has read, write, destructor 3 function pointers

  • kvm_iodevice_write() = dev->op->write() // kvm_iodevice_read/destructor also

• struct kvm_io_bus at include/linux/kvm_host.h

  • example:

    • (struct kvm_io_bus) bus->range[idx].dev

    • struct kvm_io_bus => struct kvm_io_range => struct kvm_io_device