Re: [PATCH 0/18][RFC] Nested Paging support for Nested SVM (aka NPT-Virtualization)

[Avi Kivity]

On 03/15/2010 08:27 AM, Marcelo Tosatti wrote:
> > > You should disable out of sync shadow so that l1 guest writes to
> > > l1-nested-ptables always trap.
> > >        
> > Why?  The guest is under obligation to flush the tlb if it writes to
> > a page table, and we will resync on that tlb flush.
> >      
> The guests hypervisor will not flush the tlb with invlpg for updates of
> its NPT pagetables. It'll create a new ASID, and KVM will not trap
> that.
>    

We'll get a kvm_set_cr3() on the next vmrun.

> > > And in the trap case, you'd have to
> > > invalidate l2 shadow pagetable entries that used the (now obsolete)
> > > l1-nested-ptable entry. Does that happen automatically?
> > >        
> > What do you mean by 'l2 shadow ptable entries'?  There are the
> > guest's page tables (ordinary direct mapped, unless the guest's
> > guest is also running an npt-enabled hypervisor), and the host page
> > tables.  When the guest writes to each page table, we invalidate the
> > shadows.
> >      
> With 'l2 shadow ptable entries' i mean the shadow pagetables that
> translate GPA-L2 ->  HPA.
>    

kvm_mmu_pte_write() will invalidate those sptes and will also install 
new translations if possible.

Beautiful, isn't it?

--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.

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