Re: [PATCH rdma-next 0/5] Cleanup of CONFIG_INFINIBAND_ON_DEMAND_PAGING usage

On Fri, Dec 21, 2018 at 03:59:54PM +0200, Leon Romanovsky wrote:

quoted

diff --git a/drivers/infiniband/core/umem.c b/drivers/infiniband/core/umem.c
index c6144df47ea47e..c2615b6bb68841 100644
+++ b/drivers/infiniband/core/umem.c

@@ -95,6 +95,9 @@ struct ib_umem *ib_umem_get(struct ib_ucontext *context, unsigned long addr,
 	struct scatterlist *sg, *sg_list_start;
 	unsigned int gup_flags = FOLL_WRITE;

+	if ((access & IB_ACCESS_ON_DEMAND) && !context->invalidate_range)
+		return ERR_PTR(-EOPNOTSUPP);
+

My expectation that we won't be in this state because it is too far away
from entry where we could check and prevent unsupported access.

uverbs entry point -> driver code -> ib_umem_get
  ^^^^ this is better place to check right flags.

I view umem as the proper core entry point here. We should never
allow to create an ODP umem without driver support.

quoted

@@ -3607,13 +3606,15 @@ static int ib_uverbs_ex_query_device(struct uverbs_attr_bundle *attrs)

 	copy_query_dev_fields(ucontext, &resp.base, &attr);

-	resp.odp_caps.general_caps = attr.odp_caps.general_caps;
-	resp.odp_caps.per_transport_caps.rc_odp_caps =
-		attr.odp_caps.per_transport_caps.rc_odp_caps;
-	resp.odp_caps.per_transport_caps.uc_odp_caps =
-		attr.odp_caps.per_transport_caps.uc_odp_caps;
-	resp.odp_caps.per_transport_caps.ud_odp_caps =
-		attr.odp_caps.per_transport_caps.ud_odp_caps;
+	if (ib_dev->attrs.device_cap_flags & IB_DEVICE_ON_DEMAND_PAGING) {
+		resp.odp_caps.general_caps = attr.odp_caps.general_caps;
+		resp.odp_caps.per_transport_caps.rc_odp_caps =
+			attr.odp_caps.per_transport_caps.rc_odp_caps;
+		resp.odp_caps.per_transport_caps.uc_odp_caps =
+			attr.odp_caps.per_transport_caps.uc_odp_caps;
+		resp.odp_caps.per_transport_caps.ud_odp_caps =
+			attr.odp_caps.per_transport_caps.ud_odp_caps;
+	}

"attr" is initialized to zero, there is no need to place those odp_caps under "if",

It is not zero, it is the result of query_device - and broken drivers
should not be allowed to put non-zero values here..

quoted

 	resp.timestamp_mask = attr.timestamp_mask;
 	resp.hca_core_clock = attr.hca_core_clock;

diff --git a/drivers/infiniband/hw/mlx5/main.c b/drivers/infiniband/hw/mlx5/main.c
index ff131e4c874ec5..df8366fb0142d6 100644
+++ b/drivers/infiniband/hw/mlx5/main.c

@@ -923,9 +923,11 @@ static int mlx5_ib_query_device(struct ib_device *ibdev,
 	props->hca_core_clock = MLX5_CAP_GEN(mdev, device_frequency_khz);
 	props->timestamp_mask = 0x7FFFFFFFFFFFFFFFULL;

-	if (MLX5_CAP_GEN(mdev, pg))
-		props->device_cap_flags |= IB_DEVICE_ON_DEMAND_PAGING;
-	props->odp_caps = dev->odp_caps;
+	if (IS_ENABLED(CONFIG_INFINIBAND_ON_DEMAND_PAGING)) {
+		if (MLX5_CAP_GEN(mdev, pg))
+			props->device_cap_flags |= IB_DEVICE_ON_DEMAND_PAGING;
+		props->odp_caps = dev->odp_caps;
+	}

I accepted your claim about odp_caps being SW properties, but why did
you place device_cap_flags under CONFIG_INFINIBAND_ON_DEMAND_PAGING?
Especially when it is set based on HW capability.

My claim was about device_cap_flags, it indicates the SW capability
for ODP, it has nothing to do with HW.

quoted

 	if (MLX5_CAP_GEN(mdev, cd))
 		props->device_cap_flags |= IB_DEVICE_CROSS_CHANNEL;

@@ -1761,7 +1763,8 @@ static struct ib_ucontext *mlx5_ib_alloc_ucontext(struct ib_device *ibdev,
 	if (err)
 		goto out_sys_pages;

-	context->ibucontext.invalidate_range = &mlx5_ib_invalidate_range;
+	if (ibdev->attrs.device_cap_flags & IB_DEVICE_ON_DEMAND_PAGING)
+		context->ibucontext.invalidate_range = &mlx5_ib_invalidate_range;

We are not supposed to call to invalidate_range() if umem is not ODP.
It means that the below "if" is redundant.

I want to see all function pointers the driver does not implement set
to NULL... I suppose this needs to have an IS_ENABLED too since
mlx5_ib_invalidate_range is in odp.c

quoted

diff --git a/drivers/infiniband/hw/mlx5/mem.c b/drivers/infiniband/hw/mlx5/mem.c
index 9f90be296ee0f7..22827ba4b6d8eb 100644
+++ b/drivers/infiniband/hw/mlx5/mem.c

@@ -150,7 +150,7 @@ void __mlx5_ib_populate_pas(struct mlx5_ib_dev *dev, struct ib_umem *umem,
 	struct scatterlist *sg;
 	int entry;

-	if (umem->is_odp) {
+	if (IS_ENABLED(CONFIG_INFINIBAND_ON_DEMAND_PAGING) && umem->is_odp) {

How can we have is_odp == True and CONFIG_INFINIBAND_ON_DEMAND_PAGING = n?
mlx5 code expects that if CONFIG_INFINIBAND_ON_DEMAND_PAGING is not set,
all occurrences of is_odp are false.

Whenver you see the IS_ENABLED it is just size optimizing code. The
compiler can't know that is_odp == FALSE, so the extra check is
needed.

quoted

diff --git a/drivers/infiniband/hw/mlx5/mr.c b/drivers/infiniband/hw/mlx5/mr.c
index 65d07c111d42a7..8183e94da5a1ea 100644
+++ b/drivers/infiniband/hw/mlx5/mr.c

@@ -1332,12 +1332,14 @@ struct ib_mr *mlx5_ib_reg_user_mr(struct ib_pd *pd, u64 start, u64 length,
 	mlx5_ib_dbg(dev, "start 0x%llx, virt_addr 0x%llx, length 0x%llx, access_flags 0x%x\n",
 		    start, virt_addr, length, access_flags);

-	if (IS_ENABLED(CONFIG_INFINIBAND_ON_DEMAND_PAGING) && !start &&
-	    length == U64_MAX) {
+	if (!start && length == U64_MAX) {
 		if (!(access_flags & IB_ACCESS_ON_DEMAND) ||
 		    !(dev->odp_caps.general_caps & IB_ODP_SUPPORT_IMPLICIT))
 			return ERR_PTR(-EINVAL);

+		if (!IS_ENABLED(CONFIG_INFINIBAND_ON_DEMAND_PAGING))
+			return ERR_PTR(-EOPNOTSUPP);
+

I tried to preserve previous behavior and that piece of code was simply
skipped if CONFIG_INFINIBAND_ON_DEMAND_PAGING is not set. You will
return -EOPNOTSUPP in new code. It can be right, it can be wrong, but
that change should be standalone.

Sure - it is a bug that it checks arguments differently depending on
compile options.

Jason