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

Gleb Natapov
2014-07-15T12:09:21Z

On Tue, Jul 15, 2014 at 01:52:40PM +0200, Jan Kiszka wrote:
> On 2014-07-14 16:58, Gleb Natapov wrote:
> >>>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> >>>> index ffbe557..7080eda 100644
> >>>> --- a/arch/x86/kvm/x86.c
> >>>> +++ b/arch/x86/kvm/x86.c
> >>>> @@ -5929,6 +5929,18 @@ static void vcpu_scan_ioapic(struct kvm_vcpu *vcpu)
> >>>> kvm_apic_update_tmr(vcpu, tmr);
> >>>> }
> >>>>
> >>>> +static void vcpu_reload_apic_access_page(struct kvm_vcpu *vcpu)
> >>>> +{
> >>>> + /*
> >>>> + * When the page is being migrated, GUP will wait till the migrate
> >>>> + * entry is replaced with the new pte entry pointing to the new page.
> >>>> + */
> >>>> + struct page *page = gfn_to_page_no_pin(vcpu->kvm,
> >>>> + APIC_DEFAULT_PHYS_BASE>> PAGE_SHIFT);
> >>> If you do not use kvm->arch.apic_access_page to get current address why not drop it entirely?
> >>>
> >>
> >> I should also update kvm->arch.apic_access_page here. It is used in other
> >> places
> >> in kvm, so I don't think we should drop it. Will update the patch.
> > What other places? The only other place I see is in nested kvm code and you can call
> > gfn_to_page_no_pin() there instead of using kvm->arch.apic_access_page directly. But
> > as far as I see nested kvm code cannot handle change of APIC_ACCESS_ADDR phys address.
> > If APIC_ACCESS_ADDR changes during nested guest run, non nested vmcs will still have old
> > physical address. One way to fix that is to set KVM_REQ_APIC_PAGE_RELOAD during nested exit.
>
> I cannot follow your concerns yet. Specifically, how should
> APIC_ACCESS_ADDR (the VMCS field, right?) change while L2 is running? We
> currently pin/unpin on L1->L2/L2->L1, respectively. Or what do you mean?
>
I am talking about this case:
if (cpu_has_secondary_exec_ctrls()) {a
} else {
exec_control |=
SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES;
vmcs_write64(APIC_ACCESS_ADDR,
page_to_phys(vcpu->kvm->arch.apic_access_page));
}
We do not pin here.

--
Gleb.