[RFC PATCH 04/17] KVM: arm64: Protect page table traversal with RCU

[Oliver Upton]

Use RCU to safely traverse the page tables in parallel; the tables
themselves will only be freed from an RCU synchronized context. Don't
even bother with adding support to hyp, and instead just assume
exclusive access of the page tables.

Signed-off-by: Oliver Upton <oupton at google.com>
---
 arch/arm64/kvm/hyp/pgtable.c | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index 5b64fbca8a93..d4699f698d6e 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -132,9 +132,28 @@ static kvm_pte_t kvm_phys_to_pte(u64 pa)
 	return pte;
 }
 
+
+#if defined(__KVM_NVHE_HYPERVISOR__)
+static inline void kvm_pgtable_walk_begin(void)
+{}
+
+static inline void kvm_pgtable_walk_end(void)
+{}
+
+#define kvm_dereference_ptep	rcu_dereference_raw
+#else
+#define kvm_pgtable_walk_begin	rcu_read_lock
+
+#define kvm_pgtable_walk_end	rcu_read_unlock
+
+#define kvm_dereference_ptep	rcu_dereference
+#endif
+
 static kvm_pte_t *kvm_pte_follow(kvm_pte_t pte, struct kvm_pgtable_mm_ops *mm_ops)
 {
-	return mm_ops->phys_to_virt(kvm_pte_to_phys(pte));
+	kvm_pte_t __rcu *ptep = mm_ops->phys_to_virt(kvm_pte_to_phys(pte));
+
+	return kvm_dereference_ptep(ptep);
 }
 
 static void kvm_clear_pte(kvm_pte_t *ptep)
@@ -288,7 +307,9 @@ int kvm_pgtable_walk(struct kvm_pgtable *pgt, u64 addr, u64 size,
 		.walker	= walker,
 	};
 
+	kvm_pgtable_walk_begin();
 	return _kvm_pgtable_walk(&walk_data);
+	kvm_pgtable_walk_end();
 }
 
 struct leaf_walk_data {
-- 
2.36.0.rc0.470.gd361397f0d-goog