Patch "drm/i915/gvt: Fix possible recursive locking issue" has been added to the 4.12-stable tree

From 62d02fd1f807bf5a259a242c483c9fb98a242630 Mon Sep 17 00:00:00 2001

From 7f56c30bd0a232822aca38d288da475613bdff9b Mon Sep 17 00:00:00 2001

-----Original Message-----
From: [email protected] [mailto:[email protected]]
Sent: Tuesday, July 25, 2017 12:39 PM
To: Dong, Chuanxiao <[email protected]>
Cc: [email protected]; [email protected]
Subject: Patch "drm/i915/gvt: Fix possible recursive locking issue" has been added to the 4.12-stable tree

This is a note to let you know that I've just added the patch titled

drm/i915/gvt: Fix possible recursive locking issue

to the 4.12-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-
queue.git;a=summary

The filename of the patch is:
drm-i915-gvt-fix-possible-recursive-locking-issue.patch
and it can be found in the queue-4.12 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From 62d02fd1f807bf5a259a242c483c9fb98a242630 Mon Sep 17 00:00:00 2001
From: Chuanxiao Dong <[email protected]>
Date: Mon, 26 Jun 2017 15:20:49 +0800
Subject: drm/i915/gvt: Fix possible recursive locking issue

From: Chuanxiao Dong <[email protected]>

commit 62d02fd1f807bf5a259a242c483c9fb98a242630 upstream.

vfio_unpin_pages will hold a read semaphore however it is already hold in the same thread by vfio ioctl. It will cause below warning:

[ 5102.127454] ============================================
[ 5102.133379] WARNING: possible recursive locking detected [ 5102.139304]
4.12.0-rc4+ #3 Not tainted [ 5102.143483] -----------------------------------------
---
[ 5102.149407] qemu-system-x86/1620 is trying to acquire lock:
[ 5102.155624]  (&container->group_lock){++++++}, at: [<ffffffff817768c6>]
vfio_unpin_pages+0x96/0xf0 [ 5102.165626] but task is already holding lock:
[ 5102.172134]  (&container->group_lock){++++++}, at: [<ffffffff8177728f>]
vfio_fops_unl_ioctl+0x5f/0x280 [ 5102.182522] other info that might help us
debug this:
[ 5102.189806]  Possible unsafe locking scenario:

[ 5102.196411]        CPU0
[ 5102.199136]        ----
[ 5102.201861]   lock(&container->group_lock);
[ 5102.206527]   lock(&container->group_lock);
[ 5102.211191]
---
 drivers/gpu/drm/i915/gvt/gvt.h   |    3 ++
 drivers/gpu/drm/i915/gvt/kvmgt.c |   55
+++++++++++++++++++++++++++++++--------
 2 files changed, 48 insertions(+), 10 deletions(-)

drivers/gpu/drm/i915/gvt/gvt.h +3 -0

@@ -183,6 +183,9 @@ struct intel_vgpu {
 		struct kvm *kvm;
 		struct work_struct release_work;
 		atomic_t released;
+		struct work_struct unpin_work;
+		spinlock_t unpin_lock; /* To protect unpin_list */
+		struct list_head unpin_list;
 	} vdev;
 #endif
 };

drivers/gpu/drm/i915/gvt/kvmgt.c +1 -0

@@ -78,6 +78,7 @@ struct gvt_dma {
 	struct rb_node node;
 	gfn_t gfn;
 	unsigned long iova;
+	struct list_head list;
 };
 
 static inline bool handle_valid(unsigned long handle) @@ -166,6 +167,7 @@

static void gvt_cache_add(struct intel_v

drivers/gpu/drm/i915/gvt/kvmgt.c +35 -9

 	new->gfn = gfn;
 	new->iova = iova;
+	INIT_LIST_HEAD(&new->list);
 
 	mutex_lock(&vgpu->vdev.cache_lock);
 	while (*link) {

@@ -197,26 +199,52 @@ static void __gvt_cache_remove_entry(str
 	kfree(entry);
 }
 
-static void gvt_cache_remove(struct intel_vgpu *vgpu, gfn_t gfn)
+static void intel_vgpu_unpin_work(struct work_struct *work)
 {
+	struct intel_vgpu *vgpu = container_of(work, struct intel_vgpu,
+					       vdev.unpin_work);
 	struct device *dev = mdev_dev(vgpu->vdev.mdev);
 	struct gvt_dma *this;
-	unsigned long g1;
-	int rc;
+	unsigned long gfn;
+
+	for (;;) {
+		spin_lock(&vgpu->vdev.unpin_lock);
+		if (list_empty(&vgpu->vdev.unpin_list)) {
+			spin_unlock(&vgpu->vdev.unpin_lock);
+			break;
+		}
+		this = list_first_entry(&vgpu->vdev.unpin_list,
+					struct gvt_dma, list);
+		list_del(&this->list);
+		spin_unlock(&vgpu->vdev.unpin_lock);
+
+		gfn = this->gfn;
+		vfio_unpin_pages(dev, &gfn, 1);
+		kfree(this);
+	}
+}
+
+static bool gvt_cache_mark_remove(struct intel_vgpu *vgpu, gfn_t gfn) {
+	struct gvt_dma *this;
 
 	mutex_lock(&vgpu->vdev.cache_lock);
 	this  = __gvt_cache_find(vgpu, gfn);
 	if (!this) {
 		mutex_unlock(&vgpu->vdev.cache_lock);
-		return;
+		return false;
 	}
-
-	g1 = gfn;
 	gvt_dma_unmap_iova(vgpu, this->iova);
-	rc = vfio_unpin_pages(dev, &g1, 1);
-	WARN_ON(rc != 1);
-	__gvt_cache_remove_entry(vgpu, this);
+	/* remove this from rb tree */
+	rb_erase(&this->node, &vgpu->vdev.cache);
 	mutex_unlock(&vgpu->vdev.cache_lock);
+
+	/* put this to the unpin_list */
+	spin_lock(&vgpu->vdev.unpin_lock);
+	list_move_tail(&this->list, &vgpu->vdev.unpin_list);
+	spin_unlock(&vgpu->vdev.unpin_lock);
+
+	return true;
 }
 
 static void gvt_cache_init(struct intel_vgpu *vgpu) @@ -453,6 +481,9 @@

static int intel_vgpu_create(struct kobj

drivers/gpu/drm/i915/gvt/kvmgt.c +5 -2

 	}
 
 	INIT_WORK(&vgpu->vdev.release_work, intel_vgpu_release_work);
+	INIT_WORK(&vgpu->vdev.unpin_work, intel_vgpu_unpin_work);
+	spin_lock_init(&vgpu->vdev.unpin_lock);
+	INIT_LIST_HEAD(&vgpu->vdev.unpin_list);
 
 	vgpu->vdev.mdev = mdev;
 	mdev_set_drvdata(mdev, vgpu);

@@ -482,6 +513,7 @@ static int intel_vgpu_iommu_notifier(str
 	struct intel_vgpu *vgpu = container_of(nb,
 					struct intel_vgpu,
 					vdev.iommu_notifier);
+	bool sched_unmap = false;
 
 	if (action == VFIO_IOMMU_NOTIFY_DMA_UNMAP) {
 		struct vfio_iommu_type1_dma_unmap *unmap = data; @@
-491,7 +523,10 @@ static int intel_vgpu_iommu_notifier(str
 		end_gfn = gfn + unmap->size / PAGE_SIZE;
 
 		while (gfn < end_gfn)
-			gvt_cache_remove(vgpu, gfn++);
+			sched_unmap |= gvt_cache_mark_remove(vgpu,

gfn++);

drivers/gpu/drm/i915/gvt/kvmgt.c +3 -0

+
+		if (sched_unmap)
+			schedule_work(&vgpu->vdev.unpin_work);
 	}
 
 	return NOTIFY_OK;

Patches currently in stable-queue which might be from [email protected] are

queue-4.12/drm-i915-gvt-fix-possible-recursive-locking-issue.patch queue-4.12/drm-i915-gvt-fix-inconsistent-locks-holding-sequence.patch queue-4.12/vfio-remove-unnecessary-uses-of- vfio_container.group_lock.patch

Hi Greg,

This fix is not needed and the issue is actually fixed by below which you just picked for 4.12-stable tree.

Quoted 1 line

From 7f56c30bd0a232822aca38d288da475613bdff9b Mon Sep 17 00:00:00 2001

From: Alex Williamson <[email protected]>
Date: Fri, 7 Jul 2017 15:37:38 -0600
Subject: vfio: Remove unnecessary uses of vfio_container.group_lock

From: Alex Williamson <[email protected]>

commit 7f56c30bd0a232822aca38d288da475613bdff9b upstream.

And this patch is already reverted. So please drop this one.