IB/mthca: Avoid changing userspace ABI to handle DMA write barrier attribute

Commit cb9fbc5c ("IB: expand ib_umem_get() prototype") changed the
mthca userspace ABI to provide a way for userspace to indicate which
memory regions need the DMA write barrier attribute.  However, it is
possible to handle this without breaking existing userspace, by having
the mthca kernel driver recognize whether it is talking to old or new
userspace, depending on the size of the register MR structure passed in.

The only potential drawback of this is that is allows old userspace
(which has a bug with DMA ordering on large SGI Altix systems) to
continue to run on new kernels, but the advantage of allowing old
userspace to continue to work on unaffected systems seems to outweigh
this, and we can print a warning to push people to upgrade their
userspace.

Signed-off-by: Roland Dreier <rolandd@cisco.com>

1 files changed, 13 insertions, 1 deletions

diff --git a/drivers/infiniband/hw/mthca/mthca_provider.c b/drivers/infiniband/hw/mthca/mthca_provider.c
index 2a9f460cf061..be34f99ca625 100644
--- a/drivers/infiniband/hw/mthca/mthca_provider.c
+++ b/drivers/infiniband/hw/mthca/mthca_provider.c
@@ -39,6 +39,8 @@
 #include <rdma/ib_smi.h>
 #include <rdma/ib_umem.h>
 #include <rdma/ib_user_verbs.h>
+
+#include <linux/sched.h>
 #include <linux/mm.h>
 
 #include "mthca_dev.h"
@@ -367,6 +369,8 @@ static struct ib_ucontext *mthca_alloc_ucontext(struct ib_device *ibdev,
 		return ERR_PTR(-EFAULT);
 	}
 
+	context->reg_mr_warned = 0;
+
 	return &context->ibucontext;
 }
 
@@ -1013,7 +1017,15 @@ static struct ib_mr *mthca_reg_user_mr(struct ib_pd *pd, u64 start, u64 length,
 	int err = 0;
 	int write_mtt_size;
 
-	if (ib_copy_from_udata(&ucmd, udata, sizeof ucmd))
+	if (udata->inlen - sizeof (struct ib_uverbs_cmd_hdr) < sizeof ucmd) {
+		if (!to_mucontext(pd->uobject->context)->reg_mr_warned) {
+			mthca_warn(dev, "Process '%s' did not pass in MR attrs.\n",
+				   current->comm);
+			mthca_warn(dev, "  Update libmthca to fix this.\n");
+		}
+		++to_mucontext(pd->uobject->context)->reg_mr_warned;
+		ucmd.mr_attrs = 0;
+	} else if (ib_copy_from_udata(&ucmd, udata, sizeof ucmd))
 		return ERR_PTR(-EFAULT);
 
 	mr = kmalloc(sizeof *mr, GFP_KERNEL);