Re: [RFC] nvme: set block size during namespace validation

[Minwoo Im <minwoo.im.dev@gmail.com>]

Hello,

On 20-12-23 16:49:04, Christoph Hellwig wrote:
> set_blocksize just sets the block sise used for buffer heads and should
> not be called by the driver.  blkdev_get updates the block size, so
> you must already have the fd re-reading the partition table open?
> I'm not entirely sure how we can work around this except by avoiding
> buffer head I/O in the partition reread code.  Note that this affects
> all block drivers where the block size could change at runtime.

Thank you Christoph for your comment on this.

Agreed.  BLKRRPART leads us to block_read_full_page which takes buffer
heads for I/O.

Yes, __blkdev_get() sets i_blkbits of block device inode via
set_init_blocksize.  And Yes again as nvme-cli already opened the block
device fd and requests the BLKRRPART with that fd.  Also, __bdev_get()
only updates the i_blkbits(blocksize) in case bdev->bd_openers == 0 which
is the first time to open this block device.

Then, how about having NVMe driver prevent underflow case for the
request->__data_len is smaller than the logical block size like:

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index ce1b61519441..030353d203bf 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -803,7 +803,11 @@ static inline blk_status_t nvme_setup_rw(struct nvme_ns *ns,
        cmnd->rw.opcode = op;
        cmnd->rw.nsid = cpu_to_le32(ns->head->ns_id);
        cmnd->rw.slba = cpu_to_le64(nvme_sect_to_lba(ns, blk_rq_pos(req)));
-       cmnd->rw.length = cpu_to_le16((blk_rq_bytes(req) >> ns->lba_shift) - 1);
+
+       if (unlikely(blk_rq_bytes(req) < (1 << ns->lba_shift)))
+               cmnd->rw.length = 0;
+       else
+               cmnd->rw.length = cpu_to_le16((blk_rq_bytes(req) >> ns->lba_shift) - 1);
 
        if (req_op(req) == REQ_OP_WRITE && ctrl->nr_streams)
                nvme_assign_write_stream(ctrl, req, &control, &dsmgmt);

Thanks,