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

[Vincent Donnefort]

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 at 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");
+		}
+
 	}
 
 	return 0;
-- 
2.55.0.rc2.803.g1fd1e6609c-goog