[PATCH v6 10/18] 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>
Tested-by: Fuad Tabba <fuad.tabba@linux.dev>
---
 arch/arm64/include/asm/kvm_hcall.h |  1 +
 arch/arm64/kvm/pkvm.c              | 50 +++++++++++++++++++++++++++---
 2 files changed, 47 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_hcall.h b/arch/arm64/include/asm/kvm_hcall.h
index 8a6c2506fdeb..9f09eb11193f 100644
--- a/arch/arm64/include/asm/kvm_hcall.h
+++ b/arch/arm64/include/asm/kvm_hcall.h
@@ -24,6 +24,7 @@ typedef u16 pkvm_handle_t;
 
 enum pkvm_topup_id {
 	PKVM_TOPUP_HYP_ALLOC,
+	NR_PKVM_TOPUP_HYP_IDS,
 	PKVM_TOPUP_HYP_ALLOC_SELFTEST,
 };
 
diff --git a/arch/arm64/kvm/pkvm.c b/arch/arm64/kvm/pkvm.c
index 7821f2592eba..ea96744f41fb 100644
--- a/arch/arm64/kvm/pkvm.c
+++ b/arch/arm64/kvm/pkvm.c
@@ -133,7 +133,7 @@ static unsigned long __pkvm_hyp_reclaim(enum pkvm_topup_id id, unsigned long tar
 	return reclaimed;
 }
 
-static __maybe_unused unsigned long pkvm_hyp_reclaim(enum pkvm_topup_id id, unsigned long target)
+static unsigned long pkvm_hyp_reclaim(enum pkvm_topup_id id, unsigned long target)
 {
 	unsigned long reclaimed = 0;
 
@@ -154,7 +154,7 @@ static __maybe_unused unsigned long pkvm_hyp_reclaim(enum pkvm_topup_id id, unsi
 	return reclaimed;
 }
 
-static __maybe_unused unsigned long pkvm_hyp_reclaimable(enum pkvm_topup_id id)
+static unsigned long pkvm_hyp_reclaimable(enum pkvm_topup_id id)
 {
 	return kvm_call_hyp_nvhe(__pkvm_hyp_reclaimable, id);
 }
@@ -360,8 +360,39 @@ void __init pkvm_selftests(void)
 #endif
 }
 
+static unsigned long pkvm_shrinker_count(struct shrinker *shrink, struct shrink_control *sc)
+{
+	unsigned long reclaimable = 0;
+	int id;
+
+	for (id = 0; id < NR_PKVM_TOPUP_HYP_IDS; id++)
+		reclaimable += pkvm_hyp_reclaimable(id);
+
+	return reclaimable ?: SHRINK_EMPTY;
+}
+
+static unsigned long pkvm_shrinker_scan(struct shrinker *shrink, struct shrink_control *sc)
+{
+	unsigned long reclaimed = 0;
+	int id;
+
+	sc->nr_scanned = 0;
+
+	for (id = 0; id < NR_PKVM_TOPUP_HYP_IDS; id++) {
+		unsigned long r = pkvm_hyp_reclaim(id, sc->nr_to_scan - sc->nr_scanned);
+
+		reclaimed += r;
+		sc->nr_scanned += r;
+		if (sc->nr_scanned >= sc->nr_to_scan)
+			break;
+	}
+
+	return reclaimed ?: SHRINK_STOP;
+}
+
 static int __init finalize_pkvm(void)
 {
+	struct shrinker *pkvm_shrinker;
 	int ret;
 
 	if (!is_protected_kvm_enabled() || !is_kvm_arm_initialised())
@@ -377,10 +408,21 @@ static int __init finalize_pkvm(void)
 	kmemleak_free_part_phys(hyp_mem_base, hyp_mem_size);
 
 	ret = pkvm_drop_host_privileges();
-	if (ret)
+	if (ret) {
 		pr_err("Failed to finalize Hyp protection: %d\n", ret);
+		return ret;
+	}
 
-	return ret;
+	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;
 }
 device_initcall_sync(finalize_pkvm);
 
-- 
2.56.0.rc1.315.gc6ed9934b7-goog