[PATCH 5.10 114/145] KVM: x86/mmu: Ensure TDP MMU roots are freed after yield

Greg Kroah-Hartman
2021-01-11T13:23:20Z

From: Ben Gardon <bgardon@google.com>

commit a889ea54b3daa63ee1463dc19ed699407d61458b upstream.

Many TDP MMU functions which need to perform some action on all TDP MMU
roots hold a reference on that root so that they can safely drop the MMU
lock in order to yield to other threads. However, when releasing the
reference on the root, there is a bug: the root will not be freed even
if its reference count (root_count) is reduced to 0.

To simplify acquiring and releasing references on TDP MMU root pages, and
to ensure that these roots are properly freed, move the get/put operations
into another TDP MMU root iterator macro.

Moving the get/put operations into an iterator macro also helps
simplify control flow when a root does need to be freed. Note that using
the list_for_each_entry_safe macro would not have been appropriate in
this situation because it could keep a pointer to the next root across
an MMU lock release + reacquire, during which time that root could be
freed.

Reported-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Fixes: faaf05b00aec ("kvm: x86/mmu: Support zapping SPTEs in the TDP MMU")
Fixes: 063afacd8730 ("kvm: x86/mmu: Support invalidate range MMU notifier for TDP MMU")
Fixes: a6a0b05da9f3 ("kvm: x86/mmu: Support dirty logging for the TDP MMU")
Fixes: 14881998566d ("kvm: x86/mmu: Support disabling dirty logging for the tdp MMU")
Signed-off-by: Ben Gardon <bgardon@google.com>
Message-Id: <20210107001935.3732070-1-bgardon@google.com>
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/x86/kvm/mmu/tdp_mmu.c | 104 ++++++++++++++++++++-------------------------
1 file changed, 48 insertions(+), 56 deletions(-)

--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -42,7 +42,48 @@ void kvm_mmu_uninit_tdp_mmu(struct kvm *
WARN_ON(!list_empty(&kvm->arch.tdp_mmu_roots));
}

-#define for_each_tdp_mmu_root(_kvm, _root) \
+static void tdp_mmu_put_root(struct kvm *kvm, struct kvm_mmu_page *root)
+{
+ if (kvm_mmu_put_root(kvm, root))
+ kvm_tdp_mmu_free_root(kvm, root);
+}
+
+static inline bool tdp_mmu_next_root_valid(struct kvm *kvm,
+ struct kvm_mmu_page *root)
+{
+ lockdep_assert_held(&kvm->mmu_lock);
+
+ if (list_entry_is_head(root, &kvm->arch.tdp_mmu_roots, link))
+ return false;
+
+ kvm_mmu_get_root(kvm, root);
+ return true;
+
+}
+
+static inline struct kvm_mmu_page *tdp_mmu_next_root(struct kvm *kvm,
+ struct kvm_mmu_page *root)
+{
+ struct kvm_mmu_page *next_root;
+
+ next_root = list_next_entry(root, link);
+ tdp_mmu_put_root(kvm, root);
+ return next_root;
+}
+
+/*
+ * Note: this iterator gets and puts references to the roots it iterates over.
+ * This makes it safe to release the MMU lock and yield within the loop, but
+ * if exiting the loop early, the caller must drop the reference to the most
+ * recent root. (Unless keeping a live reference is desirable.)
+ */
+#define for_each_tdp_mmu_root_yield_safe(_kvm, _root) \
+ for (_root = list_first_entry(&_kvm->arch.tdp_mmu_roots, \
+ typeof(*_root), link); \
+ tdp_mmu_next_root_valid(_kvm, _root); \
+ _root = tdp_mmu_next_root(_kvm, _root))
+
+#define for_each_tdp_mmu_root(_kvm, _root) \
list_for_each_entry(_root, &_kvm->arch.tdp_mmu_roots, link)

bool is_tdp_mmu_root(struct kvm *kvm, hpa_t hpa)
@@ -439,18 +480,9 @@ bool kvm_tdp_mmu_zap_gfn_range(struct kv
struct kvm_mmu_page *root;
bool flush = false;

- for_each_tdp_mmu_root(kvm, root) {
- /*
- * Take a reference on the root so that it cannot be freed if
- * this thread releases the MMU lock and yields in this loop.
- */
- kvm_mmu_get_root(kvm, root);
-
+ for_each_tdp_mmu_root_yield_safe(kvm, root)
flush |= zap_gfn_range(kvm, root, start, end, true);

- kvm_mmu_put_root(kvm, root);
- }
-
return flush;
}

@@ -609,13 +641,7 @@ static int kvm_tdp_mmu_handle_hva_range(
int ret = 0;
int as_id;

- for_each_tdp_mmu_root(kvm, root) {
- /*
- * Take a reference on the root so that it cannot be freed if
- * this thread releases the MMU lock and yields in this loop.
- */
- kvm_mmu_get_root(kvm, root);
-
+ for_each_tdp_mmu_root_yield_safe(kvm, root) {
as_id = kvm_mmu_page_as_id(root);
slots = __kvm_memslots(kvm, as_id);
kvm_for_each_memslot(memslot, slots) {
@@ -637,8 +663,6 @@ static int kvm_tdp_mmu_handle_hva_range(
ret |= handler(kvm, memslot, root, gfn_start,
gfn_end, data);
}
-
- kvm_mmu_put_root(kvm, root);
}

return ret;
@@ -826,21 +850,13 @@ bool kvm_tdp_mmu_wrprot_slot(struct kvm
int root_as_id;
bool spte_set = false;

- for_each_tdp_mmu_root(kvm, root) {
+ for_each_tdp_mmu_root_yield_safe(kvm, root) {
root_as_id = kvm_mmu_page_as_id(root);
if (root_as_id != slot->as_id)
continue;

- /*
- * Take a reference on the root so that it cannot be freed if
- * this thread releases the MMU lock and yields in this loop.
- */
- kvm_mmu_get_root(kvm, root);
-
spte_set |= wrprot_gfn_range(kvm, root, slot->base_gfn,
slot->base_gfn + slot->npages, min_level);
-
- kvm_mmu_put_root(kvm, root);
}

return spte_set;
@@ -894,21 +910,13 @@ bool kvm_tdp_mmu_clear_dirty_slot(struct
int root_as_id;
bool spte_set = false;

- for_each_tdp_mmu_root(kvm, root) {
+ for_each_tdp_mmu_root_yield_safe(kvm, root) {
root_as_id = kvm_mmu_page_as_id(root);
if (root_as_id != slot->as_id)
continue;

- /*
- * Take a reference on the root so that it cannot be freed if
- * this thread releases the MMU lock and yields in this loop.
- */
- kvm_mmu_get_root(kvm, root);
-
spte_set |= clear_dirty_gfn_range(kvm, root, slot->base_gfn,
slot->base_gfn + slot->npages);
-
- kvm_mmu_put_root(kvm, root);
}

return spte_set;
@@ -1017,21 +1025,13 @@ bool kvm_tdp_mmu_slot_set_dirty(struct k
int root_as_id;
bool spte_set = false;

- for_each_tdp_mmu_root(kvm, root) {
+ for_each_tdp_mmu_root_yield_safe(kvm, root) {
root_as_id = kvm_mmu_page_as_id(root);
if (root_as_id != slot->as_id)
continue;

- /*
- * Take a reference on the root so that it cannot be freed if
- * this thread releases the MMU lock and yields in this loop.
- */
- kvm_mmu_get_root(kvm, root);
-
spte_set |= set_dirty_gfn_range(kvm, root, slot->base_gfn,
slot->base_gfn + slot->npages);
-
- kvm_mmu_put_root(kvm, root);
}
return spte_set;
}
@@ -1077,21 +1077,13 @@ void kvm_tdp_mmu_zap_collapsible_sptes(s
struct kvm_mmu_page *root;
int root_as_id;

- for_each_tdp_mmu_root(kvm, root) {
+ for_each_tdp_mmu_root_yield_safe(kvm, root) {
root_as_id = kvm_mmu_page_as_id(root);
if (root_as_id != slot->as_id)
continue;

- /*
- * Take a reference on the root so that it cannot be freed if
- * this thread releases the MMU lock and yields in this loop.
- */
- kvm_mmu_get_root(kvm, root);
-
zap_collapsible_spte_range(kvm, root, slot->base_gfn,
slot->base_gfn + slot->npages);
-
- kvm_mmu_put_root(kvm, root);
}
}