Protect the contents of the TDP MMU roots list with RCU in preparation
for a future patch which will allow the iterator macro to be used under
the MMU lock in read mode.
Signed-off-by: Ben Gardon <bgardon@xxxxxxxxxx>
---
arch/x86/kvm/mmu/tdp_mmu.c | 64 +++++++++++++++++++++-----------------
1 file changed, 36 insertions(+), 28 deletions(-)
diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 1f0b2d6124a2..d255125059c4 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -50,6 +50,22 @@ static void tdp_mmu_free_sp(struct kvm_mmu_page *sp)
kmem_cache_free(mmu_page_header_cache, sp);
}
+/*
+ * This is called through call_rcu in order to free TDP page table memory
+ * safely with respect to other kernel threads that may be operating on
+ * the memory.
+ * By only accessing TDP MMU page table memory in an RCU read critical
+ * section, and freeing it after a grace period, lockless access to that
+ * memory won't use it after it is freed.
+ */
+static void tdp_mmu_free_sp_rcu_callback(struct rcu_head *head)
+{
+ struct kvm_mmu_page *sp = container_of(head, struct kvm_mmu_page,
+ rcu_head);
+
+ tdp_mmu_free_sp(sp);
+}
+
void kvm_tdp_mmu_put_root(struct kvm *kvm, struct kvm_mmu_page *root)
{
gfn_t max_gfn = 1ULL << (shadow_phys_bits - PAGE_SHIFT);
@@ -61,11 +77,13 @@ void kvm_tdp_mmu_put_root(struct kvm *kvm, struct kvm_mmu_page *root)
WARN_ON(!root->tdp_mmu_page);
- list_del(&root->link);
+ spin_lock(&kvm->arch.tdp_mmu_pages_lock);
+ list_del_rcu(&root->link);
+ spin_unlock(&kvm->arch.tdp_mmu_pages_lock);
zap_gfn_range(kvm, root, 0, max_gfn, false);
- tdp_mmu_free_sp(root);
+ call_rcu(&root->rcu_head, tdp_mmu_free_sp_rcu_callback);
}
/*
@@ -82,18 +100,21 @@ static struct kvm_mmu_page *tdp_mmu_next_root(struct kvm *kvm,
lockdep_assert_held_write(&kvm->mmu_lock);
+ rcu_read_lock();
+
if (prev_root)
- next_root = list_next_entry(prev_root, link);
+ next_root = list_next_or_null_rcu(&kvm->arch.tdp_mmu_roots,
+ &prev_root->link,
+ typeof(*prev_root), link);
else
- next_root = list_first_entry(&kvm->arch.tdp_mmu_roots,
- typeof(*next_root), link);
+ next_root = list_first_or_null_rcu(&kvm->arch.tdp_mmu_roots,
+ typeof(*next_root), link);
- while (!list_entry_is_head(next_root, &kvm->arch.tdp_mmu_roots, link) &&
- !kvm_tdp_mmu_get_root(kvm, next_root))
- next_root = list_next_entry(next_root, link);
+ while (next_root && !kvm_tdp_mmu_get_root(kvm, next_root))
+ next_root = list_next_or_null_rcu(&kvm->arch.tdp_mmu_roots,
+ &next_root->link, typeof(*next_root), link);
- if (list_entry_is_head(next_root, &kvm->arch.tdp_mmu_roots, link))
- next_root = NULL;
+ rcu_read_unlock();
if (prev_root)
kvm_tdp_mmu_put_root(kvm, prev_root);
@@ -114,7 +135,8 @@ static struct kvm_mmu_page *tdp_mmu_next_root(struct kvm *kvm,
/* Only safe under the MMU lock in write mode, without yielding. */
#define for_each_tdp_mmu_root(_kvm, _root) \
- list_for_each_entry(_root, &_kvm->arch.tdp_mmu_roots, link)
+ list_for_each_entry_rcu(_root, &_kvm->arch.tdp_mmu_roots, link, \
+ lockdep_is_held_write(&kvm->mmu_lock))
static union kvm_mmu_page_role page_role_for_level(struct kvm_vcpu *vcpu,
int level)
@@ -168,28 +190,14 @@ hpa_t kvm_tdp_mmu_get_vcpu_root_hpa(struct kvm_vcpu *vcpu)
root = alloc_tdp_mmu_page(vcpu, 0, vcpu->arch.mmu->shadow_root_level);
refcount_set(&root->tdp_mmu_root_count, 1);
- list_add(&root->link, &kvm->arch.tdp_mmu_roots);
+ spin_lock(&kvm->arch.tdp_mmu_pages_lock);
+ list_add_rcu(&root->link, &kvm->arch.tdp_mmu_roots);
+ spin_unlock(&kvm->arch.tdp_mmu_pages_lock);
out:
return __pa(root->spt);
}
-/*
- * This is called through call_rcu in order to free TDP page table memory
- * safely with respect to other kernel threads that may be operating on
- * the memory.
- * By only accessing TDP MMU page table memory in an RCU read critical
- * section, and freeing it after a grace period, lockless access to that
- * memory won't use it after it is freed.
- */
-static void tdp_mmu_free_sp_rcu_callback(struct rcu_head *head)
-{
- struct kvm_mmu_page *sp = container_of(head, struct kvm_mmu_page,
- rcu_head);
-
- tdp_mmu_free_sp(sp);
-}
-
static void handle_changed_spte(struct kvm *kvm, int as_id, gfn_t gfn,
u64 old_spte, u64 new_spte, int level,
bool shared);
--
2.31.0.291.g576ba9dcdaf-goog
