[PATCH RESEND rdma-rc] RDMA/mlx5: Add dummy umem to IB_MR_TYPE_DM

[Leon Romanovsky]

From: Alaa Hleihel <alaa@xxxxxxxxxx>

After the cited patch, and for the case of IB_MR_TYPE_DM that doesn't
have a umem (even though it is a user MR), function mlx5_free_priv_descs()
will think that it's a kernel MR, leading to wrongly accessing mr->descs
that will get wrong values in the union which leads to attempting to
release resources that were not allocated in the first place.

For example:
 DMA-API: mlx5_core 0000:08:00.1: device driver tries to free DMA memory it has not allocated [device address=0x0000000000000000] [size=0 bytes]
 WARNING: CPU: 8 PID: 1021 at kernel/dma/debug.c:961 check_unmap+0x54f/0x8b0
 RIP: 0010:check_unmap+0x54f/0x8b0
 Call Trace:
  debug_dma_unmap_page+0x57/0x60
  mlx5_free_priv_descs+0x57/0x70 [mlx5_ib]
  mlx5_ib_dereg_mr+0x1fb/0x3d0 [mlx5_ib]
  ib_dereg_mr_user+0x60/0x140 [ib_core]
  uverbs_destroy_uobject+0x59/0x210 [ib_uverbs]
  uobj_destroy+0x3f/0x80 [ib_uverbs]
  ib_uverbs_cmd_verbs+0x435/0xd10 [ib_uverbs]
  ? uverbs_finalize_object+0x50/0x50 [ib_uverbs]
  ? lock_acquire+0xc4/0x2e0
  ? lock_acquired+0x12/0x380
  ? lock_acquire+0xc4/0x2e0
  ? lock_acquire+0xc4/0x2e0
  ? ib_uverbs_ioctl+0x7c/0x140 [ib_uverbs]
  ? lock_release+0x28a/0x400
  ib_uverbs_ioctl+0xc0/0x140 [ib_uverbs]
  ? ib_uverbs_ioctl+0x7c/0x140 [ib_uverbs]
  __x64_sys_ioctl+0x7f/0xb0
  do_syscall_64+0x38/0x90

Fix it by adding a dummy umem to IB_MR_TYPE_DM MRs.

Fixes: f18ec4223117 ("RDMA/mlx5: Use a union inside mlx5_ib_mr")
Signed-off-by: Alaa Hleihel <alaa@xxxxxxxxxx>
Signed-off-by: Leon Romanovsky <leonro@xxxxxxxxxx>
---
RESEND: https://lore.kernel.org/all/9c6478b70dc23cfec3a7bfc345c30ff817e7e799.1631660866.git.leonro@xxxxxxxxxx

Our request to drop that original patch was because mr-->umem pointer is checked
in rereg flow for the DM MRs with expectation to have NULL there. However DM is
blocked for the rereg path in the commit 5ccbf63f87a3 ("IB/uverbs: Prevent
reregistration of DM_MR to regular MR"), and the checks in mlx5_ib are redundant.

Thanks
---
 drivers/infiniband/core/umem.c  | 21 +++++++++++++++++++++
 drivers/infiniband/hw/mlx5/mr.c |  5 +++++
 include/rdma/ib_umem.h          |  5 +++++
 3 files changed, 31 insertions(+)

diff --git a/drivers/infiniband/core/umem.c b/drivers/infiniband/core/umem.c
index 86d479772fbc..a2f9c922bdd9 100644
--- a/drivers/infiniband/core/umem.c
+++ b/drivers/infiniband/core/umem.c
@@ -260,6 +260,27 @@ struct ib_umem *ib_umem_get(struct ib_device *device, unsigned long addr,
 }
 EXPORT_SYMBOL(ib_umem_get);
 
+/**
+ * ib_umem_get_dummy - Create an empty umem
+ *
+ * @device: IB device to connect UMEM
+ */
+struct ib_umem *ib_umem_get_dummy(struct ib_device *device)
+{
+	struct ib_umem *umem;
+
+	umem = kzalloc(sizeof(*umem), GFP_KERNEL);
+	if (!umem)
+		return ERR_PTR(-ENOMEM);
+
+	umem->ibdev = device;
+	umem->owning_mm = current->mm;
+	mmgrab(umem->owning_mm);
+
+	return umem;
+}
+EXPORT_SYMBOL(ib_umem_get_dummy);
+
 /**
  * ib_umem_release - release memory pinned with ib_umem_get
  * @umem: umem struct to release
diff --git a/drivers/infiniband/hw/mlx5/mr.c b/drivers/infiniband/hw/mlx5/mr.c
index 3be36ebbf67a..6fbc281a8881 100644
--- a/drivers/infiniband/hw/mlx5/mr.c
+++ b/drivers/infiniband/hw/mlx5/mr.c
@@ -1389,6 +1389,11 @@ static struct ib_mr *mlx5_ib_get_dm_mr(struct ib_pd *pd, u64 start_addr,
 	kfree(in);
 
 	set_mr_fields(dev, mr, length, acc);
+	mr->umem = ib_umem_get_dummy(&dev->ib_dev);
+	if (IS_ERR(mr->umem)) {
+		err = PTR_ERR(mr->umem);
+		goto err_free;
+	}
 
 	return &mr->ibmr;
 
diff --git a/include/rdma/ib_umem.h b/include/rdma/ib_umem.h
index 5ae9dff74dac..fd20b1610050 100644
--- a/include/rdma/ib_umem.h
+++ b/include/rdma/ib_umem.h
@@ -98,6 +98,7 @@ static inline void __rdma_umem_block_iter_start(struct ib_block_iter *biter,
 
 struct ib_umem *ib_umem_get(struct ib_device *device, unsigned long addr,
 			    size_t size, int access);
+struct ib_umem *ib_umem_get_dummy(struct ib_device *device);
 void ib_umem_release(struct ib_umem *umem);
 int ib_umem_copy_from(void *dst, struct ib_umem *umem, size_t offset,
 		      size_t length);
@@ -153,6 +154,10 @@ static inline struct ib_umem *ib_umem_get(struct ib_device *device,
 {
 	return ERR_PTR(-EOPNOTSUPP);
 }
+static struct ib_umem *ib_umem_get_dummy(struct ib_device *device)
+{
+	return ERR_PTR(-EOPNOTSUPP);
+}
 static inline void ib_umem_release(struct ib_umem *umem) { }
 static inline int ib_umem_copy_from(void *dst, struct ib_umem *umem, size_t offset,
 		      		    size_t length) {
-- 
2.31.1