On Tue, Oct 10, 2023 at 07:09:54PM +0530, Kanchan Joshi wrote:
The case is for the single interleaved buffer with both data and metadata. When the driver sends this buffer to blk_rq_map_user_iov(), it may make a copy of it. This kernel buffer will be used for DMA rather than user buffer. If the user-buffer is short, the kernel buffer is also short.
Yes. Note that we'll corrupt memory either way, so user vs kernel does not matter.
Does this explanation help? I can move the part to a separate patch.
Definitively separate function please, not sure if a separate patch is required.
Yes, not io_uring specific. Just that I was not sure on (i) whether to go back that far in history, and (ii) what patch to tag.
I think the one that adds the original problem is:
63263d60e0f9f37bfd5e6a1e83a62f0e62fc459f Author: Keith Busch kbusch@kernel.org Date: Tue Aug 29 17:46:04 2017 -0400
nvme: Use metadata for passthrough commands
/* Exclude commands that do not have nlb in cdw12 */if (!nvme_nlb_in_cdw12(c->common.opcode))return true;So we can still get exactly the same corruption for all commands that are not known? That's not a very safe way to deal with the issue..
Given the way things are in NVMe, I do not find a better way. Maybe another day for commands that do (or can do) things very differently for nlb and PI representation.
Fixing just a subset of these problems is pointless. If people want to use metadata on vendor specific commands they need to work with NVMe to figure out a generic way to pass the length.