Re: Where is the entry of hypercalls in kvm?

Balachandar
2010-06-30T15:02:31Z

On Wed, Jun 30, 2010 at 10:59 AM, Balachandar <bala1486@gmail.com> wrote:
> On Wed, Jun 30, 2010 at 4:17 AM, Peter Teoh <htmldeveloper@gmail.com> wrote:
>> Your questioned is answered here:
>>
>> http://www.spinics.net/lists/kvm/msg37526.html
>>
>> And check this paper out:
>>
>> http://ozlabs.org/~rusty/virtio-spec/virtio-paper.pdf
>>
>> The general concept to remember is that QEMU and KVM just execute the
>> input as binary stream....it does not know what "functions" it is
>> executing...so the binary stream can be any OS (windows / Linux
>> etc)....QEMU just setup the basic block (call basic blocks
>> translation) mechanism, and then execute it block by block.   Each
>> block by definition is demarcated by a branch/jump etc.   Within the
>> block if there is any privilege instruction, (eg, write MSR registers,
>> load LDT registers etc), then a transition will be made from guest in
>> QEMU into KVM to update the VMCB/VMCS information.   (these terms are
>> from Intel/AMD manual).
>>
>> I have not seen any IOCTL calls in QEMU, but I suspect ultimately it
>> should drop to a VMRUN (for AMD, Intel called it VMLAUNCH or VMRESUME)
>> calls inside KVM, which can be found here:
>>
>> arch/x86/kvm/
>>
>> And the AMD specific virtualization is done in svm.c whereas that of
>> vmx.c is for Intel.
>>
>> Copying the remark in vmx.c:
>>
>> /*
>>  * The exit handlers return 1 if the exit was handled fully and guest execution
>>  * may resume.  Otherwise they set the kvm_run parameter to indicate what needs
>>  * to be done to userspace and return 0.
>>  */
>> static int (*kvm_vmx_exit_handlers[])(struct kvm_vcpu *vcpu) = {
>>        [EXIT_REASON_EXCEPTION_
>>
>> And after reading the Intel manual, u will understand that "exit" here
>> actually refers to the special set of privilege intel instructions,
>> which upon being executed by the guest OS, will immediately caused and
>> VMEXIT condition, and these are handled by the above handler in
>> kvm.ko.
>>
>> To know the entry point INTO the guest OS (ie, when the guest code
>> will first be run) first must understand that all these VMX operation
>> are a state machine (3, VMLAUNCH, VMRESUME and VMEXIT).   Once inside
>> the VMRESUME state, there is no way for it to access any of the hosts
>> resources, only accessible after VMEXIT is triggered.
>>
>> All key APIs are defined here (for Intel) (this is KVM specific, Xen
>> has another mechanism, :
>>
>> static struct kvm_x86_ops vmx_x86_ops = {
>>        .cpu_has_kvm_support = cpu_has_kvm_support,
>>        .disabled_by_bios = vmx_disabled_by_bios,
>>        .hardware_setup = hardware_setup,
>>        .hardware_unsetup = hardware_unsetup,
>> ...
>>        .run = vmx_vcpu_run,
>>        .handle_exit = vmx_handle_exit,
>>        .skip_emulated_instruction = skip_emulated_instruction,
>>        .set_interrupt_shadow = vmx_set_interrupt_shadow,
>>
>> and vmx_vcpu_run() is the the answer to your question.....i supposed?
>>
>> Perhaps another summary resource:
>>
>> http://download.microsoft.com/download/9/8/f/98f3fe47-dfc3-4e74-92a3-088782200fe7/TWAR05015_WinHEC05.ppt
>>
>> As for virtio_net.....it is implemented in
>> drivers/net/virtio_net.c......not sure what is your question?
>>
> Thank you for your elaborate answer. My question is what is the code
> in qemu-kvm that is called when kick function is called in virtio_net?
> The kick function does some ioport write and this will be trapped by
> the hypervisor into kvm. Then kvm will call some function in qemu-kvm
> userspace for io emulation. So for this particular case virtio_net
> what is the function in qemu-kvm that will be called when kick is
> encountered in the guest?
>
I already got the answer from Alexander. If anyone is looking the
function is virtio_net_write in hw/virtio_pci.c