From 3b6384dac14a306fd3d8e4357b5191a6f2b7f52e Mon Sep 17 00:00:00 2001 From: Jiri Pirko Date: Sun, 17 May 2026 16:13:11 +0200 Subject: [PATCH] RDMA/umem: Block plain userspace memory registration under CoCo bounce 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. Link: https://patch.msgid.link/r/20260517141311.2409230-3-jiri@resnulli.us Signed-off-by: Jiri Pirko Signed-off-by: Jason Gunthorpe --- 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 89311fe65619..e424a9de66c1 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.