[PATCH v2 23/27] KVM: x86/mmu: Assert that correct locks are held for page write-tracking

[Sean Christopherson <seanjc@xxxxxxxxxx>]

When adding/removing gfns to/from write-tracking, assert that mmu_lock
is held for write, and that either slots_lock or kvm->srcu is held.
mmu_lock must be held for write to protect gfn_write_track's refcount,
and SRCU or slots_lock must be held to protect the memslot itself.

Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
 arch/x86/kvm/mmu/page_track.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/mmu/page_track.c b/arch/x86/kvm/mmu/page_track.c
index 1993db4578e5..ffcd7ac66f9e 100644
--- a/arch/x86/kvm/mmu/page_track.c
+++ b/arch/x86/kvm/mmu/page_track.c
@@ -12,6 +12,7 @@
  */
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
+#include <linux/lockdep.h>
 #include <linux/kvm_host.h>
 #include <linux/rculist.h>
 
@@ -77,9 +78,6 @@ static void update_gfn_write_track(struct kvm_memory_slot *slot, gfn_t gfn,
  * add guest page to the tracking pool so that corresponding access on that
  * page will be intercepted.
  *
- * It should be called under the protection both of mmu-lock and kvm->srcu
- * or kvm->slots_lock.
- *
  * @kvm: the guest instance we are interested in.
  * @slot: the @gfn belongs to.
  * @gfn: the guest page.
@@ -87,6 +85,11 @@ static void update_gfn_write_track(struct kvm_memory_slot *slot, gfn_t gfn,
 void kvm_write_track_add_gfn(struct kvm *kvm, struct kvm_memory_slot *slot,
 			     gfn_t gfn)
 {
+	lockdep_assert_held_write(&kvm->mmu_lock);
+
+	lockdep_assert_once(lockdep_is_held(&kvm->slots_lock) ||
+			    srcu_read_lock_held(&kvm->srcu));
+
 	if (WARN_ON(!kvm_page_track_write_tracking_enabled(kvm)))
 		return;
 
@@ -107,9 +110,6 @@ EXPORT_SYMBOL_GPL(kvm_write_track_add_gfn);
  * remove the guest page from the tracking pool which stops the interception
  * of corresponding access on that page.
  *
- * It should be called under the protection both of mmu-lock and kvm->srcu
- * or kvm->slots_lock.
- *
  * @kvm: the guest instance we are interested in.
  * @slot: the @gfn belongs to.
  * @gfn: the guest page.
@@ -117,6 +117,11 @@ EXPORT_SYMBOL_GPL(kvm_write_track_add_gfn);
 void kvm_write_track_remove_gfn(struct kvm *kvm,
 				struct kvm_memory_slot *slot, gfn_t gfn)
 {
+	lockdep_assert_held_write(&kvm->mmu_lock);
+
+	lockdep_assert_once(lockdep_is_held(&kvm->slots_lock) ||
+			    srcu_read_lock_held(&kvm->srcu));
+
 	if (WARN_ON(!kvm_page_track_write_tracking_enabled(kvm)))
 		return;
 
-- 
2.40.0.rc1.284.g88254d51c5-goog