On Fri, Mar 12, 2010 at 09:36:41AM +0200, Avi Kivity wrote: > On 03/11/2010 10:58 PM, Marcelo Tosatti wrote: > > > >>>Can't you translate l2_gpa -> l1_gpa walking the current l1 nested > >>>pagetable, and pass that to the kvm tdp fault path (with the correct > >>>context setup)? > >>If I understand your suggestion correctly, I think thats exactly whats > >>done in the patches. Some words about the design: > >> > >>For nested-nested we need to shadow the l1-nested-ptable on the host. > >>This is done using the vcpu->arch.mmu context which holds the l1 paging > >>modes while the l2 is running. On a npt-fault from the l2 we just > >>instrument the shadow-ptable code. This is the common case. because it > >>happens all the time while the l2 is running. > >OK, makes sense now, I was missing the fact that the l1-nested-ptable > >needs to be shadowed and l1 translations to it must be write protected. > > Shadow converts (gva -> gpa -> hpa) to (gva -> hpa) or (ngpa -> gpa > -> hpa) to (ngpa -> hpa) equally well. In the second case npt still > does (ngva -> ngpa). > > >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. > Unsync makes just as much sense for nnpt. Think of khugepaged in > the guest eating a page table and spitting out a PDE. > > >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. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
