[PATCH 11/17] KVM: arm64: Add a shrinker for pKVM

[Vincent Donnefort <vdonnefort@google.com>]

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 8bb2c7422cc8..34e6fab29210 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -2677,6 +2677,18 @@ 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)
 {
@@ -2823,6 +2835,8 @@ static int __init init_hyp_mode(void)
 	kvm_hyp_init_symbols();
 
 	if (is_protected_kvm_enabled()) {
+		struct shrinker *shrinker;
+
 		if (IS_ENABLED(CONFIG_ARM64_PTR_AUTH_KERNEL) &&
 		    cpus_have_final_cap(ARM64_HAS_ADDRESS_AUTH))
 			pkvm_hyp_init_ptrauth();
@@ -2843,6 +2857,16 @@ static int __init init_hyp_mode(void)
 			kvm_err("Failed to init hyp memory protection\n");
 			goto out_err;
 		}
+
+		shrinker = shrinker_alloc(0, "pkvm");
+		if (shrinker) {
+			shrinker->count_objects = pkvm_shrinker_count;
+			shrinker->scan_objects = pkvm_shrinker_scan;
+			shrinker_register(shrinker);
+		} else {
+			kvm_err("Failed to register shrinker for pKVM\n");
+		}
+
 	}
 
 	return 0;
-- 
2.54.0.631.ge1b05301d1-goog