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RDMA/umem: Block plain userspace memory registration under CoCo bounce

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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 <jiri@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
This commit is contained in:
Jiri Pirko 2026-05-17 16:13:11 +02:00 committed by Jason Gunthorpe
parent d7a40b5194
commit 3b6384dac1
1 changed files with 3 additions and 0 deletions
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3
drivers/infiniband/core/umem.c
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@ -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.