Re: [PATCH] KVM: MMU: Replace role.glevels with role.cr4_pae

[Avi Kivity <avi@redhat.com>]

On 04/14/2010 07:20 PM, Avi Kivity wrote:
> There is no real distinction between glevels=3 and glevels=4; both have
> exactly the same format and the code is treated exactly the same way.  Drop
> role.glevels and replace is with role.cr4_pae (which is meaningful).  This
> simplifies the code a bit.
>
> As a side effect, it allows sharing shadow page tables between pae and
> longmode guest page tables at the same guest page.
>    

>
>   static int kvm_sync_page(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp)
>   {
> -	if (sp->role.glevels != vcpu->arch.mmu.root_level) {
> +	if (sp->role.cr4_pae != !!is_pae(vcpu)) {
>   		kvm_mmu_zap_page(vcpu->kvm, sp);
>   		return 1;
>   	}
>    

This bit confuses me a little.  Why is it needed?  It will never hit 
from mmu_sync_children(), and as for kvm_mmu_get_page(), it will simply 
zap unrelated pages?

Is it related to the restriction that we can only unsync if we have just 
one shadow page for a gfn?  That's somewhat artificial (and hurts nonpae 
guests, and guests with linear page tables).

-- 
error compiling committee.c: too many arguments to function