Re: [PATCH v2 11/18] KVM: arm64: Add a shrinker for pKVM

[Vincent Donnefort <vdonnefort@google.com>]

On Wed, Jul 15, 2026 at 12:20:51PM +0100, Fuad Tabba wrote:
> On Mon, 6 Jul 2026 at 18:54, Vincent Donnefort <vdonnefort@google.com> wrote:
> >
> > Integrate the pKVM memory reclaim interface with the host's memory
> > management subsystem.
> >
> > This allows the host to automatically recover unused memory fom the
> > hypervisor's heap allocator when the host is under memory pressure.
> >
> > Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
> >
> > diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> > index 50adfff75be8..3dc2b9d2c322 100644
> > --- a/arch/arm64/kvm/arm.c
> > +++ b/arch/arm64/kvm/arm.c
> > @@ -122,6 +122,8 @@ static bool vgic_present, kvm_arm_initialised;
> >
> >  static DEFINE_PER_CPU(unsigned char, kvm_hyp_initialized);
> >
> > +static struct shrinker *pkvm_shrinker;
> > +
> >  bool is_kvm_arm_initialised(void)
> >  {
> >         return kvm_arm_initialised;
> > @@ -2526,8 +2528,8 @@ static void __init teardown_hyp_mode(void)
> >                 }
> >
> >                 free_pages(kvm_nvhe_sym(kvm_arm_hyp_percpu_base)[cpu], nvhe_percpu_order());
> > -
> >         }
> > +       shrinker_free(pkvm_shrinker);
> >  }
> >
> >  static int __init do_pkvm_init(u32 hyp_va_bits)
> > @@ -2713,6 +2715,18 @@ static void pkvm_hyp_init_ptrauth(void)
> >         }
> >  }
> >
> > +static unsigned long
> > +pkvm_shrinker_count(struct shrinker *shrink, struct shrink_control *sc)
> > +{
> > +       return pkvm_hyp_reclaimable(PKVM_TOPUP_HYP_ALLOC) ?: SHRINK_EMPTY;
> > +}
> > +
> > +static unsigned long
> > +pkvm_shrinker_scan(struct shrinker *shrink, struct shrink_control *sc)
> > +{
> > +       return pkvm_hyp_reclaim(PKVM_TOPUP_HYP_ALLOC, sc->nr_to_scan);
> > +}
> > +
> >  /* Inits Hyp-mode on all online CPUs */
> >  static int __init init_hyp_mode(void)
> >  {
> > @@ -2883,6 +2897,16 @@ static int __init init_hyp_mode(void)
> >                         kvm_err("Failed to init hyp memory protection\n");
> >                         goto out_err;
> >                 }
> > +
> > +               pkvm_shrinker = shrinker_alloc(0, "pkvm");
> > +               if (pkvm_shrinker) {
> > +                       pkvm_shrinker->count_objects = pkvm_shrinker_count;
> > +                       pkvm_shrinker->scan_objects = pkvm_shrinker_scan;
> > +                       shrinker_register(pkvm_shrinker);
> > +               } else {
> > +                       kvm_err("Failed to register shrinker for pKVM\n");
> > +               }
> > +
> >         }
> 
> Sashiko might be onto something here. The shrinker goes live in
> init_hyp_mode(), but kvm_protected_mode_initialized isn't set until
> finalize_pkvm()...

I doubt the shrinker can be triggered that early... BUT 

The hyp tracing is a user of this hyp allocator and I have been working on
enabling early tracing [1] so I shall move those HVCs as well!

[1] https://lore.kernel.org/all/20260708075435.47419-2-vdonnefort@google.com/

> 
> Cheers,
> /fuad
> 
> >
> >         return 0;
> > --
> > 2.55.0.rc2.803.g1fd1e6609c-goog
> >