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

tangchen
2014-09-12T03:31:31Z

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.