diff options
| -rw-r--r-- | Documentation/virt/kvm/locking.rst | 5 | ||||
| -rw-r--r-- | include/linux/kvm_host.h | 9 | ||||
| -rw-r--r-- | virt/kvm/kvm_main.c | 54 |
3 files changed, 62 insertions, 6 deletions
diff --git a/Documentation/virt/kvm/locking.rst b/Documentation/virt/kvm/locking.rst index 1fc860c007a3..35eca377543d 100644 --- a/Documentation/virt/kvm/locking.rst +++ b/Documentation/virt/kvm/locking.rst @@ -16,6 +16,11 @@ The acquisition orders for mutexes are as follows: - kvm->slots_lock is taken outside kvm->irq_lock, though acquiring them together is quite rare. +- Unlike kvm->slots_lock, kvm->slots_arch_lock is released before + synchronize_srcu(&kvm->srcu). Therefore kvm->slots_arch_lock + can be taken inside a kvm->srcu read-side critical section, + while kvm->slots_lock cannot. + 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 8583ed3ff344..11b9b11a5e9b 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -523,6 +523,15 @@ struct kvm { #endif /* KVM_HAVE_MMU_RWLOCK */ struct mutex slots_lock; + + /* + * Protects the arch-specific fields of struct kvm_memory_slots in + * use by the VM. To be used under the slots_lock (above) or in a + * kvm->srcu critical section where acquiring the slots_lock would + * lead to deadlock with the synchronize_srcu in + * install_new_memslots. + */ + struct mutex slots_arch_lock; struct mm_struct *mm; /* userspace tied to this vm */ struct kvm_memslots __rcu *memslots[KVM_ADDRESS_SPACE_NUM]; struct kvm_vcpu *vcpus[KVM_MAX_VCPUS]; diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index d65be9461493..fa7e7ebefc79 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -909,6 +909,7 @@ static struct kvm *kvm_create_vm(unsigned long type) mutex_init(&kvm->lock); mutex_init(&kvm->irq_lock); mutex_init(&kvm->slots_lock); + mutex_init(&kvm->slots_arch_lock); INIT_LIST_HEAD(&kvm->devices); BUILD_BUG_ON(KVM_MEM_SLOTS_NUM > SHRT_MAX); @@ -1281,6 +1282,14 @@ static struct kvm_memslots *install_new_memslots(struct kvm *kvm, slots->generation = gen | KVM_MEMSLOT_GEN_UPDATE_IN_PROGRESS; rcu_assign_pointer(kvm->memslots[as_id], slots); + + /* + * Acquired in kvm_set_memslot. Must be released before synchronize + * SRCU below in order to avoid deadlock with another thread + * acquiring the slots_arch_lock in an srcu critical section. + */ + mutex_unlock(&kvm->slots_arch_lock); + synchronize_srcu_expedited(&kvm->srcu); /* @@ -1352,9 +1361,27 @@ static int kvm_set_memslot(struct kvm *kvm, struct kvm_memslots *slots; int r; + /* + * Released in install_new_memslots. + * + * Must be held from before the current memslots are copied until + * after the new memslots are installed with rcu_assign_pointer, + * then released before the synchronize srcu in install_new_memslots. + * + * When modifying memslots outside of the slots_lock, must be held + * before reading the pointer to the current memslots until after all + * changes to those memslots are complete. + * + * These rules ensure that installing new memslots does not lose + * changes made to the previous memslots. + */ + mutex_lock(&kvm->slots_arch_lock); + slots = kvm_dup_memslots(__kvm_memslots(kvm, as_id), change); - if (!slots) + if (!slots) { + mutex_unlock(&kvm->slots_arch_lock); return -ENOMEM; + } if (change == KVM_MR_DELETE || change == KVM_MR_MOVE) { /* @@ -1365,10 +1392,9 @@ static int kvm_set_memslot(struct kvm *kvm, slot->flags |= KVM_MEMSLOT_INVALID; /* - * We can re-use the old memslots, the only difference from the - * newly installed memslots is the invalid flag, which will get - * dropped by update_memslots anyway. We'll also revert to the - * old memslots if preparing the new memory region fails. + * We can re-use the memory from the old memslots. + * It will be overwritten with a copy of the new memslots + * after reacquiring the slots_arch_lock below. */ slots = install_new_memslots(kvm, as_id, slots); @@ -1380,6 +1406,17 @@ static int kvm_set_memslot(struct kvm *kvm, * - kvm_is_visible_gfn (mmu_check_root) */ kvm_arch_flush_shadow_memslot(kvm, slot); + + /* Released in install_new_memslots. */ + mutex_lock(&kvm->slots_arch_lock); + + /* + * The arch-specific fields of the memslots could have changed + * between releasing the slots_arch_lock in + * install_new_memslots and here, so get a fresh copy of the + * slots. + */ + kvm_copy_memslots(slots, __kvm_memslots(kvm, as_id)); } r = kvm_arch_prepare_memory_region(kvm, new, mem, change); @@ -1395,8 +1432,13 @@ static int kvm_set_memslot(struct kvm *kvm, return 0; out_slots: - if (change == KVM_MR_DELETE || change == KVM_MR_MOVE) + if (change == KVM_MR_DELETE || change == KVM_MR_MOVE) { + slot = id_to_memslot(slots, old->id); + slot->flags &= ~KVM_MEMSLOT_INVALID; slots = install_new_memslots(kvm, as_id, slots); + } else { + mutex_unlock(&kvm->slots_arch_lock); + } kvfree(slots); return r; } |