[PATCH rdma-next v2 2/2] RDMA/umem: block plain userspace memory registration under CoCo bounce

[Jiri Pirko <jiri@resnulli.us>]

From: Jiri Pirko <jiri@nvidia.com>

When a device requires DMA bounce buffering inside a Confidential
Computing guest, __ib_umem_get_va() cannot work. The DMA mapping layer
redirects all mappings through swiotlb bounce buffers, so the device
receives DMA addresses pointing to bounce buffer memory rather than
the user's pages. 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.

The registration would already fail later on, since the umem mapping
is requested with DMA_ATTR_REQUIRE_COHERENT and gets rejected under
is_swiotlb_force_bounce() with -EIO. Fail early with -EOPNOTSUPP
instead, so the user gets a specific error code to react to.

Signed-off-by: Jiri Pirko <jiri@nvidia.com>
---
v1->v2:
- updated patch description with mention of DMA_ATTR_REQUIRE_COHERENT
---
 drivers/infiniband/core/umem.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/infiniband/core/umem.c b/drivers/infiniband/core/umem.c
index 611d693eb9a2..b1877b83b021 100644
--- a/drivers/infiniband/core/umem.c
+++ b/drivers/infiniband/core/umem.c
@@ -167,6 +167,9 @@ static struct ib_umem *__ib_umem_get_va(struct ib_device *device,
 	int pinned, ret;
 	unsigned int gup_flags = FOLL_LONGTERM;
 
+	if (device->cc_dma_bounce)
+		return ERR_PTR(-EOPNOTSUPP);
+
 	/*
 	 * If the combination of the addr and size requested for this memory
 	 * region causes an integer overflow, return error.
-- 
2.53.0