[PATCH 09/27] drm/i915/gvt: Protect gfn hash table with dedicated mutex

[Sean Christopherson]

Add and use a new mutex, gfn_lock, to protect accesses to the hash table
used to track which gfns are write-protected when shadowing the guest's
GTT.  This fixes a bug where kvmgt_page_track_write(), which doesn't hold
kvm->mmu_lock, could race with intel_gvt_page_track_remove() and trigger
a use-after-free.

Fixing kvmgt_page_track_write() by taking kvm->mmu_lock is not an option
as mmu_lock is a r/w spinlock, and intel_vgpu_page_track_handler() might
sleep when acquiring vgpu->cache_lock deep down the callstack:

  intel_vgpu_page_track_handler()
  |
  |->  page_track->handler / ppgtt_write_protection_handler()
       |
       |-> ppgtt_handle_guest_write_page_table_bytes()
           |
           |->  ppgtt_handle_guest_write_page_table()
                |
                |-> ppgtt_handle_guest_entry_removal()
                    |
                    |-> ppgtt_invalidate_pte()
                        |
                        |-> intel_gvt_dma_unmap_guest_page()
                            |
                            |-> mutex_lock(&vgpu->cache_lock);

Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
 drivers/gpu/drm/i915/gvt/gvt.h   |  1 +
 drivers/gpu/drm/i915/gvt/kvmgt.c | 65 ++++++++++++++++++++------------
 drivers/gpu/drm/i915/gvt/vgpu.c  |  1 +
 3 files changed, 43 insertions(+), 24 deletions(-)

diff --git a/drivers/gpu/drm/i915/gvt/gvt.h b/drivers/gpu/drm/i915/gvt/gvt.h
index dbf8d7470b2c..fbfd7eafec14 100644
--- a/drivers/gpu/drm/i915/gvt/gvt.h
+++ b/drivers/gpu/drm/i915/gvt/gvt.h
@@ -176,6 +176,7 @@ struct intel_vgpu {
 	struct vfio_device vfio_device;
 	struct intel_gvt *gvt;
 	struct mutex vgpu_lock;
+	struct mutex gfn_lock;
 	int id;
 	bool active;
 	bool attached;
diff --git a/drivers/gpu/drm/i915/gvt/kvmgt.c b/drivers/gpu/drm/i915/gvt/kvmgt.c
index ca9926061cd8..a4747e153dad 100644
--- a/drivers/gpu/drm/i915/gvt/kvmgt.c
+++ b/drivers/gpu/drm/i915/gvt/kvmgt.c
@@ -366,6 +366,8 @@ __kvmgt_protect_table_find(struct intel_vgpu *info, gfn_t gfn)
 {
 	struct kvmgt_pgfn *p, *res = NULL;
 
+	lockdep_assert_held(&info->gfn_lock);
+
 	hash_for_each_possible(info->ptable, p, hnode, gfn) {
 		if (gfn == p->gfn) {
 			res = p;
@@ -388,6 +390,8 @@ static void kvmgt_protect_table_add(struct intel_vgpu *info, gfn_t gfn)
 {
 	struct kvmgt_pgfn *p;
 
+	lockdep_assert_held(&info->gfn_lock);
+
 	if (kvmgt_gfn_is_write_protected(info, gfn))
 		return;
 
@@ -1563,60 +1567,68 @@ int intel_gvt_page_track_add(struct intel_vgpu *info, u64 gfn)
 {
 	struct kvm *kvm = info->vfio_device.kvm;
 	struct kvm_memory_slot *slot;
-	int idx;
+	int idx, ret = 0;
 
 	if (!info->attached)
 		return -ESRCH;
 
+	mutex_lock(&info->gfn_lock);
+
+	if (kvmgt_gfn_is_write_protected(info, gfn))
+		goto out;
+
 	idx = srcu_read_lock(&kvm->srcu);
 	slot = gfn_to_memslot(kvm, gfn);
 	if (!slot) {
 		srcu_read_unlock(&kvm->srcu, idx);
-		return -EINVAL;
+		ret = -EINVAL;
+		goto out;
 	}
 
 	write_lock(&kvm->mmu_lock);
-
-	if (kvmgt_gfn_is_write_protected(info, gfn))
-		goto out;
-
 	kvm_slot_page_track_add_page(kvm, slot, gfn, KVM_PAGE_TRACK_WRITE);
+	write_unlock(&kvm->mmu_lock);
+
+	srcu_read_unlock(&kvm->srcu, idx);
+
 	kvmgt_protect_table_add(info, gfn);
-
 out:
-	write_unlock(&kvm->mmu_lock);
-	srcu_read_unlock(&kvm->srcu, idx);
-	return 0;
+	mutex_unlock(&info->gfn_lock);
+	return ret;
 }
 
 int intel_gvt_page_track_remove(struct intel_vgpu *info, u64 gfn)
 {
 	struct kvm *kvm = info->vfio_device.kvm;
 	struct kvm_memory_slot *slot;
-	int idx;
+	int idx, ret = 0;
 
 	if (!info->attached)
 		return 0;
 
-	idx = srcu_read_lock(&kvm->srcu);
-	slot = gfn_to_memslot(kvm, gfn);
-	if (!slot) {
-		srcu_read_unlock(&kvm->srcu, idx);
-		return -EINVAL;
-	}
-
-	write_lock(&kvm->mmu_lock);
+	mutex_lock(&info->gfn_lock);
 
 	if (!kvmgt_gfn_is_write_protected(info, gfn))
 		goto out;
 
+	idx = srcu_read_lock(&kvm->srcu);
+	slot = gfn_to_memslot(kvm, gfn);
+	if (!slot) {
+		srcu_read_unlock(&kvm->srcu, idx);
+		ret = -EINVAL;
+		goto out;
+	}
+
+	write_lock(&kvm->mmu_lock);
 	kvm_slot_page_track_remove_page(kvm, slot, gfn, KVM_PAGE_TRACK_WRITE);
+	write_unlock(&kvm->mmu_lock);
+	srcu_read_unlock(&kvm->srcu, idx);
+
 	kvmgt_protect_table_del(info, gfn);
 
 out:
-	write_unlock(&kvm->mmu_lock);
-	srcu_read_unlock(&kvm->srcu, idx);
-	return 0;
+	mutex_unlock(&info->gfn_lock);
+	return ret;
 }
 
 static void kvmgt_page_track_write(struct kvm_vcpu *vcpu, gpa_t gpa,
@@ -1627,11 +1639,13 @@ static void kvmgt_page_track_write(struct kvm_vcpu *vcpu, gpa_t gpa,
 		container_of(node, struct intel_vgpu, track_node);
 
 	mutex_lock(&info->vgpu_lock);
+	mutex_lock(&info->gfn_lock);
 
 	if (kvmgt_gfn_is_write_protected(info, gpa_to_gfn(gpa)))
 		intel_vgpu_page_track_handler(info, gpa,
 						     (void *)val, len);
 
+	mutex_unlock(&info->gfn_lock);
 	mutex_unlock(&info->vgpu_lock);
 }
 
@@ -1644,16 +1658,19 @@ static void kvmgt_page_track_flush_slot(struct kvm *kvm,
 	struct intel_vgpu *info =
 		container_of(node, struct intel_vgpu, track_node);
 
-	write_lock(&kvm->mmu_lock);
+	mutex_lock(&info->gfn_lock);
 	for (i = 0; i < slot->npages; i++) {
 		gfn = slot->base_gfn + i;
 		if (kvmgt_gfn_is_write_protected(info, gfn)) {
+			write_lock(&kvm->mmu_lock);
 			kvm_slot_page_track_remove_page(kvm, slot, gfn,
 						KVM_PAGE_TRACK_WRITE);
+			write_unlock(&kvm->mmu_lock);
+
 			kvmgt_protect_table_del(info, gfn);
 		}
 	}
-	write_unlock(&kvm->mmu_lock);
+	mutex_unlock(&info->gfn_lock);
 }
 
 void intel_vgpu_detach_regions(struct intel_vgpu *vgpu)
diff --git a/drivers/gpu/drm/i915/gvt/vgpu.c b/drivers/gpu/drm/i915/gvt/vgpu.c
index 56c71474008a..f2479781b770 100644
--- a/drivers/gpu/drm/i915/gvt/vgpu.c
+++ b/drivers/gpu/drm/i915/gvt/vgpu.c
@@ -277,6 +277,7 @@ struct intel_vgpu *intel_gvt_create_idle_vgpu(struct intel_gvt *gvt)
 	vgpu->id = IDLE_VGPU_IDR;
 	vgpu->gvt = gvt;
 	mutex_init(&vgpu->vgpu_lock);
+	mutex_init(&vgpu->gfn_lock);
 
 	for (i = 0; i < I915_NUM_ENGINES; i++)
 		INIT_LIST_HEAD(&vgpu->submission.workload_q_head[i]);
-- 
2.39.0.314.g84b9a713c41-goog