Re: [PATCH 0/4] kvm, mem-hotplug: Do not pin ept identity pagetable and apic access page.

[Tang Chen]

Hi Gleb,

On 07/03/2014 02:04 PM, Gleb Natapov wrote:
> On Thu, Jul 03, 2014 at 09:17:59AM +0800, Tang Chen wrote:
> > Hi Gleb,
> >
> > On 07/02/2014 05:00 PM, Tang Chen wrote:
> > > Hi Gleb, Marcelo,
> > >
> > > Please help to review this patch-set.
> > >
> > > NOTE: This patch-set doesn't work properly.
> > >
> > >
> > > ept identity pagetable and apic access page in kvm are pinned in memory.
> > > As a result, they cannot be migrated/hot-removed.
> > >
> > > But actually they don't need to be pinned in memory.
> > >
> > > This patch-set introduces two new vcpu requests: KVM_REQ_MIGRATE_EPT and KVM_REQ_MIGRATE_APIC.
> > > These two requests are made when the two pages are migrated by the mmu_notifier
> > > to reset the related variable to unusable value. And will also be made when
> > > ept violation happens to reset new pages.
> > >
> > >
> > > [Known problem]
> > > After this patch-set applied, the two pages can be migrated/hot-removed.
> > > But after migrating apic access page, the guest died.
> > >
> > > The host physical address of apic access page is stored in VMCS. I reset
> > > it to 0 to stop guest from accessing it when it is unmapped by
> > > kvm_mmu_notifier_invalidate_page(). And reset it to new page's host physical
> > > address in tdp_page_fault(). But it seems that guest will access apic page
> > > directly by the host physical address.
> >
> > Would you please to give some advice about this problem ?
> I haven't reviewed third patch yet, will do ASAP.

I printed some info in the kernel, and I found that mmu_notifier 
unmapped the
apic page and set VMCS APIC_ACCESS_ADDR to 0. But apic page ept 
violation didn't
happen. And the guest stopped running.

I think when guest tried to access apic page, there was no ept violation 
happened.
And as a result, VMCS APIC_ACCESS_ADDR was not correctly set.

Referring to Intel Software Developer's Manuel Vol 3B, when accessing 
apic page
using translation with a large page (2M, 4M, 1G), APIC VM_exit will not 
happen.

How do you think about this ?

Thanks. :)




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