Re: [PATCH] KVM: MMU: Disassociate direct maps from guest levels

[Marcelo Tosatti <mtosatti@redhat.com>]

On Tue, Mar 23, 2010 at 01:02:35PM +0200, Avi Kivity wrote:
> On 03/23/2010 12:51 PM, Avi Kivity wrote:
> >On 03/17/2010 08:16 PM, Marcelo Tosatti wrote:
> >>On Sun, Mar 14, 2010 at 10:22:52AM +0200, Avi Kivity wrote:
> >>>Direct maps are linear translations for a section of memory, used for
> >>>real mode or with large pages.  As such, they are independent
> >>>of the guest
> >>>levels.
> >>>
> >>>Teach the mmu about this by making page->role.glevels = 0 for
> >>>direct maps.
> >>>This allows direct maps to be shared among real mode and the
> >>>various paging
> >>>modes.
> >>>
> >>>@@ -1328,6 +1328,8 @@ static struct kvm_mmu_page
> >>>*kvm_mmu_get_page(struct kvm_vcpu *vcpu,
> >>>      role = vcpu->arch.mmu.base_role;
> >>>      role.level = level;
> >>>      role.direct = direct;
> >>>+    if (role.direct)
> >>>+        role.glevels = 0;
> >>>      role.access = access;
> >>>      if (vcpu->arch.mmu.root_level<= PT32_ROOT_LEVEL) {
> >>>          quadrant = gaddr>>  (PAGE_SHIFT + (PT64_PT_BITS * level));
> >>>-- 
> >>>1.7.0.2
> >>Isnt this what happens already, since for tdp base_role.glevels is not
> >>initialized?
> >
> >Correct.  I was thinking about the nested npt case, which will use
> >role.glevels.  Joerg, please incorporate this into your nnpt
> >patchset.
> >
> 
> Actually, incorrect.  This patch is also applicable to non-tdp
> (which is the same case as nnpt).  It will allow reusing real-mode
> direct maps and large page mappings from the various modes.  It
> won't make any performance difference, it's more a documentation aid
> that direct maps aren't dependent on the guest at all, except for
> permissions.

Sure, makes sense.