Re: [PATCH] KVM: arm: memcg awareness

[Paolo Bonzini]

On 17/03/21 11:53, Marc Zyngier wrote:
> On Wed, 17 Mar 2021 10:40:23 +0000,
> Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:
> > On 17/03/21 10:10, Marc Zyngier wrote:
> > > > @@ -366,7 +366,7 @@ static int hyp_map_walker(u64 addr, u64 end, u32 level, kvm_pte_t *ptep,
> > > >    	if (WARN_ON(level == KVM_PGTABLE_MAX_LEVELS - 1))
> > > >    		return -EINVAL;
> > > >    -	childp = (kvm_pte_t *)get_zeroed_page(GFP_KERNEL);
> > > > +	childp = (kvm_pte_t *)get_zeroed_page(GFP_KERNEL_ACCOUNT);
> > > No, this is wrong.
> > >
> > > You cannot account the hypervisor page tables to the guest because we
> > > don't ever unmap them, and that we can't distinguish two data
> > > structures from two different VMs occupying the same page.
> >
> > If you never unmap them, there should at least be a shrinker to get
> > rid of unused pages in the event of memory pressure.
>
> We don't track where these pages are coming from or whether they can
> safely be unmapped. Until we can track such ownership and deal with
> page sharing, these mappings have to stay,
>
> At most, this represent the amount of memory required to map the whole
> of the linear mapping.

Ah, these are the EL2 pages, not the stage2 page tables, right?  If so, 
sorry for the noise.

Paolo