KVM: Initialize gfn_to_pfn_cache locks in dedicated helper

Move the gfn_to_pfn_cache lock initialization to another helper and
call the new helper during VM/vCPU creation.  There are race
conditions possible due to kvm_gfn_to_pfn_cache_init()'s
ability to re-initialize the cache's locks.

For example: a race between ioctl(KVM_XEN_HVM_EVTCHN_SEND) and
kvm_gfn_to_pfn_cache_init() leads to a corrupted shinfo gpc lock.

                (thread 1)                |           (thread 2)
                                          |
 kvm_xen_set_evtchn_fast                  |
  read_lock_irqsave(&gpc->lock, ...)      |
                                          | kvm_gfn_to_pfn_cache_init
                                          |  rwlock_init(&gpc->lock)
  read_unlock_irqrestore(&gpc->lock, ...) |

Rename "cache_init" and "cache_destroy" to activate+deactivate to
avoid implying that the cache really is destroyed/freed.

Note, there more races in the newly named kvm_gpc_activate() that will
be addressed separately.

Fixes: 982ed0de4753 ("KVM: Reinstate gfn_to_pfn_cache with invalidation support")
Cc: stable@vger.kernel.org
Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Michal Luczaj <mhal@rbox.co>
[sean: call out that this is a bug fix]
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20221013211234.1318131-2-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 17 insertions, 7 deletions

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 00c3448ba7f8..18592bdf4c1b 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -1240,8 +1240,18 @@ int kvm_vcpu_write_guest(struct kvm_vcpu *vcpu, gpa_t gpa, const void *data,
 void kvm_vcpu_mark_page_dirty(struct kvm_vcpu *vcpu, gfn_t gfn);
 
 /**
- * kvm_gfn_to_pfn_cache_init - prepare a cached kernel mapping and HPA for a
- *                             given guest physical address.
+ * kvm_gpc_init - initialize gfn_to_pfn_cache.
+ *
+ * @gpc:	   struct gfn_to_pfn_cache object.
+ *
+ * This sets up a gfn_to_pfn_cache by initializing locks.  Note, the cache must
+ * be zero-allocated (or zeroed by the caller before init).
+ */
+void kvm_gpc_init(struct gfn_to_pfn_cache *gpc);
+
+/**
+ * kvm_gpc_activate - prepare a cached kernel mapping and HPA for a given guest
+ *                    physical address.
  *
  * @kvm:	   pointer to kvm instance.
  * @gpc:	   struct gfn_to_pfn_cache object.
@@ -1265,9 +1275,9 @@ void kvm_vcpu_mark_page_dirty(struct kvm_vcpu *vcpu, gfn_t gfn);
  * kvm_gfn_to_pfn_cache_check() to ensure that the cache is valid before
  * accessing the target page.
  */
-int kvm_gfn_to_pfn_cache_init(struct kvm *kvm, struct gfn_to_pfn_cache *gpc,
-			      struct kvm_vcpu *vcpu, enum pfn_cache_usage usage,
-			      gpa_t gpa, unsigned long len);
+int kvm_gpc_activate(struct kvm *kvm, struct gfn_to_pfn_cache *gpc,
+		     struct kvm_vcpu *vcpu, enum pfn_cache_usage usage,
+		     gpa_t gpa, unsigned long len);
 
 /**
  * kvm_gfn_to_pfn_cache_check - check validity of a gfn_to_pfn_cache.
@@ -1324,7 +1334,7 @@ int kvm_gfn_to_pfn_cache_refresh(struct kvm *kvm, struct gfn_to_pfn_cache *gpc,
 void kvm_gfn_to_pfn_cache_unmap(struct kvm *kvm, struct gfn_to_pfn_cache *gpc);
 
 /**
- * kvm_gfn_to_pfn_cache_destroy - destroy and unlink a gfn_to_pfn_cache.
+ * kvm_gpc_deactivate - deactivate and unlink a gfn_to_pfn_cache.
  *
  * @kvm:	   pointer to kvm instance.
  * @gpc:	   struct gfn_to_pfn_cache object.
@@ -1332,7 +1342,7 @@ void kvm_gfn_to_pfn_cache_unmap(struct kvm *kvm, struct gfn_to_pfn_cache *gpc);
  * This removes a cache from the @kvm's list to be processed on MMU notifier
  * invocation.
  */
-void kvm_gfn_to_pfn_cache_destroy(struct kvm *kvm, struct gfn_to_pfn_cache *gpc);
+void kvm_gpc_deactivate(struct kvm *kvm, struct gfn_to_pfn_cache *gpc);
 
 void kvm_sigset_activate(struct kvm_vcpu *vcpu);
 void kvm_sigset_deactivate(struct kvm_vcpu *vcpu);