Re: [PATCH 0/30] nVMX: Nested VMX, v9

[Avi Kivity <avi@redhat.com>]

On 05/16/2011 02:11 AM, Nadav Har'El wrote:
> On Thu, May 12, 2011, Avi Kivity wrote about "Re: [PATCH 0/30] nVMX: Nested VMX, v9":
> >  Ah, yes.  For live migration to work, all vmcb state must be accessible
> >  via vendor-independent accessors once an exit is completely handled.
> >  For example, GPRs are accessible via kvm_register_read(), and without
> >  nesting, interrupt state is stowed in the interrupt queue, but if you
> >  keep IDT_VECTORING_INFO live between exit and entry, you can lose it if
> >  you migrate at this point.
>
> Hi, I can quite easily save this state in a different place which is saved -
> The easiest will just be to use vmcs12, which has place for exactly the fields
> we want to save (and they are rewritten anyway when we exit to L1).

You would still need ->valid_idt_vectoring_info to know you need special 
handling, no?

> Avi, would you you like me use this sort of solution to avoid the extra
> state? Of course, considering that anyway, live migration with nested VMX
> probably still doesn't work for a dozen other reasons :(
>
> Or do you consider this not enough, and rather that it is necessary that
> nested VMX should use exactly the same logic as nested SVM does - namely,
> use tricks like SVM's "exit_required" instead of our different tricks?

I think svm is rather simple here using svm_complete_interrupts() to 
decode exit_int_info into the arch independent structures.  I don't 
think ->exit_required is a hack - it could probably be improved but I 
think it does the right thing essentially.  For example 
svm_nmi_allowed() will return true if in guest mode and NMI interception 
is enabled.

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