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-rw-r--r--Documentation/virt/kvm/locking.rst6
-rw-r--r--include/linux/kvm_host.h5
-rw-r--r--virt/kvm/kvm_main.c58
3 files changed, 65 insertions, 4 deletions
diff --git a/Documentation/virt/kvm/locking.rst b/Documentation/virt/kvm/locking.rst
index 35eca377543d..8138201efb09 100644
--- a/Documentation/virt/kvm/locking.rst
+++ b/Documentation/virt/kvm/locking.rst
@@ -21,6 +21,12 @@ The acquisition orders for mutexes are as follows:
can be taken inside a kvm->srcu read-side critical section,
while kvm->slots_lock cannot.
+- kvm->mn_active_invalidate_count ensures that pairs of
+ invalidate_range_start() and invalidate_range_end() callbacks
+ use the same memslots array. kvm->slots_lock and kvm->slots_arch_lock
+ are taken on the waiting side in install_new_memslots, so MMU notifiers
+ must not take either kvm->slots_lock or kvm->slots_arch_lock.
+
On x86:
- vcpu->mutex is taken outside kvm->arch.hyperv.hv_lock
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index de58a0890b1a..5b6a69caccb5 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -548,6 +548,11 @@ struct kvm {
struct kvm_memslots __rcu *memslots[KVM_ADDRESS_SPACE_NUM];
struct kvm_vcpu *vcpus[KVM_MAX_VCPUS];
+ /* Used to wait for completion of MMU notifiers. */
+ spinlock_t mn_invalidate_lock;
+ unsigned long mn_active_invalidate_count;
+ struct rcuwait mn_memslots_update_rcuwait;
+
/*
* created_vcpus is protected by kvm->lock, and is incremented
* at the beginning of KVM_CREATE_VCPU. online_vcpus is only
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 5cc79373827f..8f9024d65866 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -604,11 +604,9 @@ static void kvm_mmu_notifier_change_pte(struct mmu_notifier *mn,
trace_kvm_set_spte_hva(address);
/*
- * .change_pte() must be surrounded by .invalidate_range_{start,end}(),
- * and so always runs with an elevated notifier count. This obviates
- * the need to bump the sequence count.
+ * .change_pte() must be surrounded by .invalidate_range_{start,end}().
*/
- WARN_ON_ONCE(!kvm->mmu_notifier_count);
+ WARN_ON_ONCE(!READ_ONCE(kvm->mn_active_invalidate_count));
kvm_handle_hva_range(mn, address, address + 1, pte, kvm_set_spte_gfn);
}
@@ -658,6 +656,18 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
trace_kvm_unmap_hva_range(range->start, range->end);
+ /*
+ * Prevent memslot modification between range_start() and range_end()
+ * so that conditionally locking provides the same result in both
+ * functions. Without that guarantee, the mmu_notifier_count
+ * adjustments will be imbalanced.
+ *
+ * Pairs with the decrement in range_end().
+ */
+ spin_lock(&kvm->mn_invalidate_lock);
+ kvm->mn_active_invalidate_count++;
+ spin_unlock(&kvm->mn_invalidate_lock);
+
__kvm_handle_hva_range(kvm, &hva_range);
return 0;
@@ -694,9 +704,22 @@ static void kvm_mmu_notifier_invalidate_range_end(struct mmu_notifier *mn,
.flush_on_ret = false,
.may_block = mmu_notifier_range_blockable(range),
};
+ bool wake;
__kvm_handle_hva_range(kvm, &hva_range);
+ /* Pairs with the increment in range_start(). */
+ spin_lock(&kvm->mn_invalidate_lock);
+ wake = (--kvm->mn_active_invalidate_count == 0);
+ spin_unlock(&kvm->mn_invalidate_lock);
+
+ /*
+ * There can only be one waiter, since the wait happens under
+ * slots_lock.
+ */
+ if (wake)
+ rcuwait_wake_up(&kvm->mn_memslots_update_rcuwait);
+
BUG_ON(kvm->mmu_notifier_count < 0);
}
@@ -977,6 +1000,9 @@ static struct kvm *kvm_create_vm(unsigned long type)
mutex_init(&kvm->irq_lock);
mutex_init(&kvm->slots_lock);
mutex_init(&kvm->slots_arch_lock);
+ spin_lock_init(&kvm->mn_invalidate_lock);
+ rcuwait_init(&kvm->mn_memslots_update_rcuwait);
+
INIT_LIST_HEAD(&kvm->devices);
BUILD_BUG_ON(KVM_MEM_SLOTS_NUM > SHRT_MAX);
@@ -1099,6 +1125,16 @@ static void kvm_destroy_vm(struct kvm *kvm)
kvm_coalesced_mmio_free(kvm);
#if defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER)
mmu_notifier_unregister(&kvm->mmu_notifier, kvm->mm);
+ /*
+ * At this point, pending calls to invalidate_range_start()
+ * have completed but no more MMU notifiers will run, so
+ * mn_active_invalidate_count may remain unbalanced.
+ * No threads can be waiting in install_new_memslots as the
+ * last reference on KVM has been dropped, but freeing
+ * memslots would deadlock without this manual intervention.
+ */
+ WARN_ON(rcuwait_active(&kvm->mn_memslots_update_rcuwait));
+ kvm->mn_active_invalidate_count = 0;
#else
kvm_arch_flush_shadow_all(kvm);
#endif
@@ -1360,7 +1396,21 @@ static struct kvm_memslots *install_new_memslots(struct kvm *kvm,
WARN_ON(gen & KVM_MEMSLOT_GEN_UPDATE_IN_PROGRESS);
slots->generation = gen | KVM_MEMSLOT_GEN_UPDATE_IN_PROGRESS;
+ /*
+ * Do not store the new memslots while there are invalidations in
+ * progress (preparatory change for the next commit).
+ */
+ spin_lock(&kvm->mn_invalidate_lock);
+ prepare_to_rcuwait(&kvm->mn_memslots_update_rcuwait);
+ while (kvm->mn_active_invalidate_count) {
+ set_current_state(TASK_UNINTERRUPTIBLE);
+ spin_unlock(&kvm->mn_invalidate_lock);
+ schedule();
+ spin_lock(&kvm->mn_invalidate_lock);
+ }
+ finish_rcuwait(&kvm->mn_memslots_update_rcuwait);
rcu_assign_pointer(kvm->memslots[as_id], slots);
+ spin_unlock(&kvm->mn_invalidate_lock);
/*
* Acquired in kvm_set_memslot. Must be released before synchronize