KVM: mmu: Add slots_arch_lock for memslot arch fields

Add a new lock to protect the arch-specific fields of memslots if they
need to be modified in a kvm->srcu read critical section. A future
commit will use this lock to lazily allocate memslot rmaps for x86.

Signed-off-by: Ben Gardon <bgardon@google.com>
Message-Id: <20210518173414.450044-5-bgardon@google.com>
[Add Documentation/ hunk. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 9 insertions, 0 deletions

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];