Re: [PATCH v5 4/7] kvm, mem-hotplug: Reload L1' apic access page on migration in vcpu_enter_guest().

[Gleb Natapov <gleb@kernel.org>]

On Thu, Sep 11, 2014 at 04:37:39PM +0200, Paolo Bonzini wrote:
> Il 11/09/2014 16:31, Gleb Natapov ha scritto:
> >> > What if the page being swapped out is L1's APIC access page?  We don't
> >> > run prepare_vmcs12 in that case because it's an L2->L0->L2 entry, so we
> >> > need to "do something".
> > We will do something on L2->L1 exit. We will call kvm_reload_apic_access_page().
> > That is what patch 5 of this series is doing.
> 
> Sorry, I meant "the APIC access page prepared by L1" for L2's execution.
> 
> You wrote:
> 
> > if (!is_guest_mode() || !(vmcs12->secondary_vm_exec_control & ECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES))
> >     write(PIC_ACCESS_ADDR)
> > 
> > In other words if L2 shares L1 apic access page then reload, otherwise do nothing.
> 
> but in that case you have to redo nested_get_page, so "do nothing"
> doesn't work.
> 
Ah, 7/7 is new in this submission. Before that this page was still
pinned.  Looking at 7/7 now I do not see how it can work since it has no
code for mmu notifier to detect that it deals with such page and call
kvm_reload_apic_access_page().  I said to Tang previously that nested
kvm has a bunch of pinned page that are hard to deal with and suggested
to iron out non nested case first :(

--
			Gleb.