[PATCH rdma-next 1/2] RDMA/uverbs: expose CoCo DMA bounce requirement to userspace

[Jiri Pirko <jiri@resnulli.us>]

From: Jiri Pirko <jiri@nvidia.com>

In CoCo guests, device DMA to regular userspace memory does not work
because the DMA mapping layer redirects all mappings through swiotlb
bounce buffers. Since RDMA devices access registered memory directly
without CPU involvement, there is no opportunity for swiotlb to
synchronize between the bounce buffer and the original pages.

Expose this condition to userspace as IB_UVERBS_DEVICE_CC_DMA_BOUNCE
in device_cap_flags_exi.

Signed-off-by: Jiri Pirko <jiri@nvidia.com>
---
 drivers/infiniband/core/device.c     | 6 ++++++
 drivers/infiniband/core/uverbs_cmd.c | 2 ++
 include/rdma/ib_verbs.h              | 3 +++
 include/uapi/rdma/ib_user_verbs.h    | 2 ++
 4 files changed, 13 insertions(+)

diff --git a/drivers/infiniband/core/device.c b/drivers/infiniband/core/device.c
index b89efaaa81ec..ad3da92c9318 100644
--- a/drivers/infiniband/core/device.c
+++ b/drivers/infiniband/core/device.c
@@ -42,6 +42,8 @@
 #include <linux/security.h>
 #include <linux/notifier.h>
 #include <linux/hashtable.h>
+#include <linux/cc_platform.h>
+#include <linux/swiotlb.h>
 #include <rdma/rdma_netlink.h>
 #include <rdma/ib_addr.h>
 #include <rdma/ib_cache.h>
@@ -1419,6 +1421,10 @@ int ib_register_device(struct ib_device *device, const char *name,
 	 */
 	WARN_ON(dma_device && !dma_device->dma_parms);
 	device->dma_device = dma_device;
+	if (dma_device &&
+	    cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT) &&
+	    is_swiotlb_force_bounce(dma_device))
+		device->cc_dma_bounce = 1;
 
 	ret = setup_device(device);
 	if (ret)
diff --git a/drivers/infiniband/core/uverbs_cmd.c b/drivers/infiniband/core/uverbs_cmd.c
index 240f8a0cfd86..2a70774c639a 100644
--- a/drivers/infiniband/core/uverbs_cmd.c
+++ b/drivers/infiniband/core/uverbs_cmd.c
@@ -3655,6 +3655,8 @@ static int ib_uverbs_ex_query_device(struct uverbs_attr_bundle *attrs)
 	resp.timestamp_mask = attr.timestamp_mask;
 	resp.hca_core_clock = attr.hca_core_clock;
 	resp.device_cap_flags_ex = attr.device_cap_flags;
+	if (ib_dev->cc_dma_bounce)
+		resp.device_cap_flags_ex |= IB_UVERBS_DEVICE_CC_DMA_BOUNCE;
 	resp.rss_caps.supported_qpts = attr.rss_caps.supported_qpts;
 	resp.rss_caps.max_rwq_indirection_tables =
 		attr.rss_caps.max_rwq_indirection_tables;
diff --git a/include/rdma/ib_verbs.h b/include/rdma/ib_verbs.h
index 167fb924f0cf..d06071b87d96 100644
--- a/include/rdma/ib_verbs.h
+++ b/include/rdma/ib_verbs.h
@@ -275,6 +275,7 @@ enum ib_device_cap_flags {
 	IB_DEVICE_FLUSH_GLOBAL = IB_UVERBS_DEVICE_FLUSH_GLOBAL,
 	IB_DEVICE_FLUSH_PERSISTENT = IB_UVERBS_DEVICE_FLUSH_PERSISTENT,
 	IB_DEVICE_ATOMIC_WRITE = IB_UVERBS_DEVICE_ATOMIC_WRITE,
+	IB_DEVICE_CC_DMA_BOUNCE = IB_UVERBS_DEVICE_CC_DMA_BOUNCE,
 };
 
 enum ib_kernel_cap_flags {
@@ -2950,6 +2951,8 @@ struct ib_device {
 	u16                          kverbs_provider:1;
 	/* CQ adaptive moderation (RDMA DIM) */
 	u16                          use_cq_dim:1;
+	/* CoCo guest with DMA bounce buffering required */
+	u16                          cc_dma_bounce:1;
 	u8                           node_type;
 	u32			     phys_port_cnt;
 	struct ib_device_attr        attrs;
diff --git a/include/uapi/rdma/ib_user_verbs.h b/include/uapi/rdma/ib_user_verbs.h
index 3b7bd99813e9..d2aeadb6d2f9 100644
--- a/include/uapi/rdma/ib_user_verbs.h
+++ b/include/uapi/rdma/ib_user_verbs.h
@@ -1368,6 +1368,8 @@ enum ib_uverbs_device_cap_flags {
 	IB_UVERBS_DEVICE_FLUSH_PERSISTENT = 1ULL << 39,
 	/* Atomic write attributes */
 	IB_UVERBS_DEVICE_ATOMIC_WRITE = 1ULL << 40,
+	/* CoCo guest with DMA bounce buffering required */
+	IB_UVERBS_DEVICE_CC_DMA_BOUNCE = 1ULL << 41,
 };
 
 enum ib_uverbs_raw_packet_caps {
-- 
2.53.0