Re: [PATCHv2 3/6] io_uring: add support for kernel registered bvecs

[Keith Busch <kbusch@kernel.org>]

On Fri, Feb 14, 2025 at 11:30:11AM +0800, Ming Lei wrote:
> On Mon, Feb 10, 2025 at 04:56:43PM -0800, Keith Busch wrote:
> > +
> > +	node->release = release;
> > +	node->priv = rq;
> > +
> > +	nr_bvecs = blk_rq_nr_phys_segments(rq);
> > +	imu = kvmalloc(struct_size(imu, bvec, nr_bvecs), GFP_KERNEL);
> > +	if (!imu) {
> > +		kfree(node);
> > +		return -ENOMEM;
> > +	}
> > +
> > +	imu->ubuf = 0;
> > +	imu->len = blk_rq_bytes(rq);
> > +	imu->acct_pages = 0;
> > +	imu->nr_bvecs = nr_bvecs;
> > +	refcount_set(&imu->refs, 1);
> > +	node->buf = imu;
> 
> request buffer direction needs to be stored in `imu`, for READ,
> the buffer is write-only, and for WRITE, the buffer is read-only,
> which isn't different with user mapped buffer.
> 
> Meantime in read_fixed/write_fixed side or buffer lookup abstraction
> helper, the buffer direction needs to be validated.

I suppose we could add that check, but the primary use case doesn't even
use those operations. They're using uring_cmd with the FIXED flag, and
io_uring can't readily validate the data direction from that interface.