linux-kernel - Re: [PATCH 2/3] nvme: Pass pointers, not dma addresses, to nvme_get/set

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Message-ID: <20160830063651.GA32323@lst.de>
Date:   Tue, 30 Aug 2016 08:36:51 +0200
From:   Christoph Hellwig <hch@....de>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Keith Busch <keith.busch@...el.com>,
        Andy Lutomirski <luto@...nel.org>, Jens Axboe <axboe@...com>,
        linux-nvme@...ts.infradead.org, Christoph Hellwig <hch@....de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] nvme: Pass pointers, not dma addresses, to
        nvme_get/set_features()

On Mon, Aug 29, 2016 at 04:20:43PM -0700, Andy Lutomirski wrote:
> The "Set Features" command (section 5.15) Figure 103 says:
> 
> If using PRPs, this field shall not be a pointer to a PRP List as the
> data buffer may not cross more than one page boundary. If no data
> structure is used as part of the specified feature, then this field is
> not used.
> 
> Does the Linux driver use PRPs?

The Linux PCIe driver always uses PRPs - and for admin command only
Fabrics can use SGLs anyway.

> Do we need to worry about kmalloc
> returning a buffer that spans a 4k boundary but does not span a Linux
> page boundary?

Isn't kmalloc supposed to return naturally aligned buffers?