On 19/01/2015 13:34, Wincy Van wrote:
>
> Actually, there is a race window between
> vmx_deliver_nested_posted_interrupt and nested_release_vmcs12
> since posted intr delivery is async:
>
> cpu 1
> cpu 2
> (nested posted intr) (dest vcpu,
> release vmcs12)
> vmcs12 = get_vmcs12(vcpu);
> if (!is_guest_mode(vcpu) || !vmcs12) {
> r = -1;
> goto out;
> }
>
>
> kunmap(vmx->nested.current_vmcs12_page);
>
> ......
>
>
> oops! current vmcs12 is invalid.
>
> However, we have already checked that the destination vcpu
> is_in_guest_mode, and if L1
> want to destroy vmcs12(in handle_vmptrld/clear, etc..), the dest vcpu
> must have done a nested
> vmexit and a non-nested vmexit(handle_vmptr***).
>
> Hence, we can disable local interrupts while delivering nested posted
> interrupts to make sure
> we are faster than the destination vcpu. This is a bit tricky but it
> an avoid that race. I think we
> do not need to add a spin lock here. RCU does not fit this case, since
> it will introduce a
> new race window between the rcu handler and handle_vmptr**.
>
> I am wondering that whether there is a better way : )
Why not just use a spinlock?
Paolo
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