linux-kernel - Re: [PATCH v12 1/9] nvme-core: Clear any SGL flags in passthru commands

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Message-ID: <20200420222646.GA11115@redsun51.ssa.fujisawa.hgst.com>
Date:   Tue, 21 Apr 2020 07:26:46 +0900
From:   Keith Busch <kbusch@...nel.org>
To:     Logan Gunthorpe <logang@...tatee.com>
Cc:     linux-kernel@...r.kernel.org, linux-nvme@...ts.infradead.org,
        Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>, Jens Axboe <axboe@...com>,
        Chaitanya Kulkarni <Chaitanya.Kulkarni@....com>,
        Max Gurtovoy <maxg@...lanox.com>,
        Stephen Bates <sbates@...thlin.com>
Subject: Re: [PATCH v12 1/9] nvme-core: Clear any SGL flags in passthru
 commands

On Mon, Apr 20, 2020 at 10:46:52AM -0600, Logan Gunthorpe wrote:
> The host driver should decide whether to use SGLs or PRPs and they
> currently assume the flags are cleared after the call to
> nvme_setup_cmd(). However, passed-through commands may erroneously
> set these bits; so clear them for all cases.
> 
> Signed-off-by: Logan Gunthorpe <logang@...tatee.com>
> Reviewed-by: Sagi Grimberg <sagi@...mberg.me>
> ---
>  drivers/nvme/host/core.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> index 91c1bd659947..f5283b300e87 100644
> --- a/drivers/nvme/host/core.c
> +++ b/drivers/nvme/host/core.c
> @@ -756,6 +756,8 @@ blk_status_t nvme_setup_cmd(struct nvme_ns *ns, struct request *req,
>  	case REQ_OP_DRV_IN:
>  	case REQ_OP_DRV_OUT:
>  		memcpy(cmd, nvme_req(req)->cmd, sizeof(*cmd));
> +		/* passthru commands should let the driver set the SGL flags */
> +		cmd->common.flags &= ~NVME_CMD_SGL_ALL;
>  		break;

Is this really necessary? The passthrough handler currently rejects user
commands that set command flags:

static int nvme_user_cmd(struct nvme_ctrl *ctrl, struct nvme_ns *ns,
			struct nvme_passthru_cmd __user *ucmd)
{
	...
	if (cmd.flags)
		return -EINVAL;