linux-kernel - RE: [Patch v3 2/6] cifs: Allocate validate negotiation request through kmalloc

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Date:   Wed, 18 Apr 2018 13:08:53 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Tom Talpey' <tom@...pey.com>,
        "longli@...rosoft.com" <longli@...rosoft.com>,
        Steve French <sfrench@...ba.org>,
        "linux-cifs@...r.kernel.org" <linux-cifs@...r.kernel.org>,
        "samba-technical@...ts.samba.org" <samba-technical@...ts.samba.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>
CC:     "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: RE: [Patch v3 2/6] cifs: Allocate validate negotiation request
 through kmalloc

From: Tom Talpey
> Sent: 18 April 2018 12:32
...
> On 4/17/2018 8:33 PM, Long Li wrote:
> > From: Long Li <longli@...rosoft.com>
> >
> > The data buffer allocated on the stack can't be DMA'ed, and hence can't send
> > through RDMA via SMB Direct.
> 
> This comment is confusing. Any registered memory can be DMA'd, need to
> state the reason for the choice here more clearly.

The stack could be allocated with vmalloc().
In which case the pages might not be physically contiguous and there is no
(sensible) call to get the physical address required by the dma controller
(or other bus master).

	David