Re: [PATCH v3 2/3] KVM: arm64: Distinct pKVM teardown memcache for stage-2

[Vincent Donnefort <vdonnefort@google.com>]

On Wed, Mar 12, 2025 at 08:59:15AM +0000, Marc Zyngier wrote:
> On Fri, 07 Mar 2025 11:34:10 +0000,
> Vincent Donnefort <vdonnefort@google.com> wrote:
> > 
> > In order to account for memory dedicated to the stage-2 page-tables, use
> > a separated memcache when tearing down the VM.
> > 
> > Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
> > 
> > diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> > index 12691ae23d4c..ace3969e8106 100644
> > --- a/arch/arm64/include/asm/kvm_host.h
> > +++ b/arch/arm64/include/asm/kvm_host.h
> > @@ -246,6 +246,7 @@ typedef unsigned int pkvm_handle_t;
> >  struct kvm_protected_vm {
> >  	pkvm_handle_t handle;
> >  	struct kvm_hyp_memcache teardown_mc;
> > +	struct kvm_hyp_memcache stage2_teardown_mc;
> >  	bool enabled;
> >  };
> >  
> > diff --git a/arch/arm64/kvm/hyp/nvhe/pkvm.c b/arch/arm64/kvm/hyp/nvhe/pkvm.c
> > index 3927fe52a3dd..15f8d5315959 100644
> > --- a/arch/arm64/kvm/hyp/nvhe/pkvm.c
> > +++ b/arch/arm64/kvm/hyp/nvhe/pkvm.c
> > @@ -678,7 +678,7 @@ teardown_donated_memory(struct kvm_hyp_memcache *mc, void *addr, size_t size)
> >  
> >  int __pkvm_teardown_vm(pkvm_handle_t handle)
> >  {
> > -	struct kvm_hyp_memcache *mc;
> > +	struct kvm_hyp_memcache *mc, *stage2_mc;
> >  	struct pkvm_hyp_vm *hyp_vm;
> >  	struct kvm *host_kvm;
> >  	unsigned int idx;
> > @@ -706,7 +706,8 @@ int __pkvm_teardown_vm(pkvm_handle_t handle)
> >  
> >  	/* Reclaim guest pages (including page-table pages) */
> >  	mc = &host_kvm->arch.pkvm.teardown_mc;
> > -	reclaim_guest_pages(hyp_vm, mc);
> > +	stage2_mc = &host_kvm->arch.pkvm.stage2_teardown_mc;
> > +	reclaim_guest_pages(hyp_vm, stage2_mc);
> 
> This looks odd. What counts as stage-2 pages here? Or is it that
> reclaim_guest_pages() is very badly named?

Yes, this is a naming issue here. How about 

  reclaim_pgtable_pages(hyp_vm, stage2_mc);

Then I can probably drop that /* Push the metadata pages to the teardown
memcache */  comment as it is clear what is pgtable and what is meta-data?

> 
> Thanks,
> 
> 	M.
> 
> -- 
> Without deviation from the norm, progress is not possible.