From: Douglas Gilbert <dgilbert@interlog.com>
To: Logan Gunthorpe <logang@deltatee.com>, Christoph Hellwig <hch@lst.de>
Cc: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>,
Sagi Grimberg <sagi@grimberg.me>,
linux-nvme@lists.infradead.org
Subject: Re: [PATCH] nvmet-passthru: Cleanup nvmet_passthru_map_sg()
Date: Thu, 15 Oct 2020 13:24:34 -0400 [thread overview]
Message-ID: <7913172f-0125-e327-562a-aa6b842ab193@interlog.com> (raw)
In-Reply-To: <bc51aadc-eee3-cf52-0623-b3f82e1958f4@deltatee.com>
On 2020-10-15 12:01 p.m., Logan Gunthorpe wrote:
>
>
> On 2020-10-15 1:56 a.m., Christoph Hellwig wrote:
>> On Fri, Oct 09, 2020 at 05:18:16PM -0600, Logan Gunthorpe wrote:
>>> static int nvmet_passthru_map_sg(struct nvmet_req *req, struct request *rq)
>>> {
>>> - int sg_cnt = req->sg_cnt;
>>> struct scatterlist *sg;
>>> int op_flags = 0;
>>> struct bio *bio;
>>> int i, ret;
>>>
>>> + if (req->sg_cnt > BIO_MAX_PAGES)
>>> + return -EINVAL;
>>
>> Don't you need to handle larger requests as well? Or at least
>> limit MDTS?
>
> No and Yes: there is already code in nvmet_passthru_override_id_ctrl()
> to limit MDTS based on max_segments and max_hw_sectors. So any request
> that doesn't pass this check should be from a misbehaving client and an
> error should be appropriate.
Running the numbers: with PAGE_SIZE of 4096 bytes and BIO_MAX_PAGES at
256 gives 1 MiB. From memory the block layer won't accept single requests
bigger than 4 MiB (or 8 MiB). Then it is possible that the sgl was
built with sgl_alloc_order(order > 0, chainable=false) in which case
the maximum (unchained) bio carrying size goes up to:
PAGE_SIZE * (2^order) * 256
I'm using order=3 by default in my driver. So one (unchained) bio will
hold as much (or more) than the block layer will take.
Doug Gilbert
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next prev parent reply other threads:[~2020-10-15 17:24 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-09 23:18 [PATCH] nvmet-passthru: Cleanup nvmet_passthru_map_sg() Logan Gunthorpe
2020-10-13 22:26 ` Sagi Grimberg
2020-10-13 22:38 ` Douglas Gilbert
2020-10-14 0:16 ` Chaitanya Kulkarni
2020-10-14 0:20 ` Logan Gunthorpe
2020-10-14 0:25 ` Chaitanya Kulkarni
2020-10-14 15:47 ` Logan Gunthorpe
2020-10-15 7:56 ` Christoph Hellwig
2020-10-15 16:01 ` Logan Gunthorpe
2020-10-15 17:24 ` Douglas Gilbert [this message]
2020-10-15 18:01 ` Christoph Hellwig
2020-10-15 18:40 ` Logan Gunthorpe
2020-10-16 13:57 ` Christoph Hellwig
2020-10-16 16:49 ` Logan Gunthorpe
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