Re: [PATCH v2 5/5] kvm, mem-hotplug: Do not pin apic access page in memory.

Gleb Natapov
2014-07-15T14:04:20Z

On Tue, Jul 15, 2014 at 03:10:15PM +0200, Jan Kiszka wrote:
> On 2014-07-15 14:40, Gleb Natapov wrote:
> >>
> >> ......
> >> 7922 if (!vmx->nested.apic_access_page)
> >> 7923 exec_control &=
> >> 7924 ~SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES;
> >> 7925 else
> >> 7926 vmcs_write64(APIC_ACCESS_ADDR,
> >> 7927 page_to_phys(vmx->nested.apic_access_page));
> >> 7928 } else if
> >> (vm_need_virtualize_apic_accesses(vmx->vcpu.kvm)) {
> >> 7929 exec_control |=
> >> 7930 SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES;
> >> 7931 vmcs_write64(APIC_ACCESS_ADDR,
> >> 7932 page_to_phys(vcpu->kvm->arch.apic_access_page));
> >> 7933 }
> >>
> >> And yes, we have the problem you said here. We can migrate the page while L2
> >> vm is running.
> >> So I think we should enforce L2 vm to exit to L1. Right ?
> >>
> > We can request APIC_ACCESS_ADDR reload during L2->L1 vmexit emulation, so
> > if APIC_ACCESS_ADDR changes while L2 is running it will be reloaded for L1 too.
>
> How should this host-managed VMCS field possibly change while L2 is running?
>
That what "Do not pin apic access page in memory" patch is doing. It changes APIC_ACCESS_ADDR
of a current vmcs. It kicks vcpu out of a guest mode of course, but vcpu may still be in
L2 at this point, so only L2 vmcs will get new APIC_ACCESS_ADDR pointer, L1 vmcs will still have
an old one.

--
Gleb.