Qemu process in Guest

Qemu process in Guest

[Kumar, Venkat]

1. How does Qemu process start running in Guest?
2. How does a guest's I/O request get trapped into the user mode qemu process?

Thx,

Venkat

Re: Qemu process in Guest

[Avi Kivity]

Kumar, Venkat wrote:
> 1. How does Qemu process start running in Guest?
>   

qemu doesn't run in the guest.  Unless you log into the guest and start 
qemu.

But I don't think that's what you were asking?

> 2. How does a guest's I/O request get trapped into the user mode qemu process?
>   

kvm traps the I/O and returns back to userspace.

Look in libkvm/libkvm.c's handle_io() and handle_mmio().  These 
eventually call into qemu/qemu-kvm.c kvm_inb() and friends, and 
kvm_mmio_read() and kvm_mmio_write().

-- 
error compiling committee.c: too many arguments to function

Re: Qemu process in Guest

[Avi Kivity]

Kumar, Venkat wrote:
>
> Thanks for the reply.
>
>  
>
> I had wrong understanding that Qemu runs in Guest.
>
> But now I understand that *ioctl(fd, KVM_RUN, 0);* will tell KVM to 
> load the guest and whenever there is an exception in the guest, KVM 
> traps it and executes the host code post ioctl depending on the reason 
> for exit.
>
>  
>
> Can you point me to the code where the KVM traps the exception and 
> loads the host to execute the post ioctl code?
>

That's what vmx.c and svm.c in the kernel are about, look at 
vmx_vcpu_run() and svm_vcpu_run().

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.