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

[tangchen]

Hi Gleb, Paolo,

On 09/11/2014 10:47 PM, Gleb Natapov wrote:
> 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().

Since L1 and L2 share one apic page, if the page is unmapped, 
mmu_notifier will
be called, and :

 - if vcpu is in L1, a L1->L0 exit is rised. apic page's pa will be 
updated in the next
   L0->L1 entry by making vcpu request.

 - if vcpu is in L2 (is_guest_mode, right?), a L2->L0 exit is rised. 
nested_vmx_vmexit()
   will not be called since it is called in L2->L1 exit. It returns 
from vmx_vcpu_run()
   directly, right ? So we should update apic page in L0->L2 entry. 
This is also done
   by making vcpu request, right ?.

   prepare_vmcs02() is called in L1->L2 entry, and nested_vmx_vmexit() 
is called in
   L2->L1 exit. So we also need to update L1's vmcs in 
nested_vmx_vmexit() in patch 5/7.

IIUC, I think patch 1~6 has done such things.

And yes, the is_guest_mode() check is not needed.

> 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 :(

Yes, and maybe adding patch 7 is not a good idea for now.

Thanks.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/