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Wed, 18 Apr 2018 10:07:55 -0400 Received: from p3plsmtpa11-03.prod.phx3.secureserver.net ([68.178.252.104]:59920 "EHLO p3plsmtpa11-03.prod.phx3.secureserver.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752687AbeDROHy (ORCPT ); Wed, 18 Apr 2018 10:07:54 -0400 Subject: Re: [Patch v3 2/6] cifs: Allocate validate negotiation request through kmalloc To: David Laight , "longli@microsoft.com" , Steve French , "linux-cifs@vger.kernel.org" , "samba-technical@lists.samba.org" , "linux-kernel@vger.kernel.org" , "linux-rdma@vger.kernel.org" Cc: "stable@vger.kernel.org" References: <20180418003358.25098-1-longli@linuxonhyperv.com> From: Tom Talpey Message-ID: Date: Wed, 18 Apr 2018 10:07:52 -0400 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-CMAE-Envelope: MS4wfNiT0LOFN6e1EYCziSDzy+NTJi+27YOwi1IgGnqj3WIJvKFMam0XAe068TMV64q5oF/RNikHXHe94nhCrAnhQpuJsr84dKajj537xIB6NRGU8/KcmU2n Lr7FE3nMQBIhy7F3fwlh0pvi0LaMd1yF0xN+q4kCRAMDx/H0KzO5ZNykmmn/CemRILwkjiRn7YBd65AY24qO+w4vC106IjxQ1PJYvuBxHgeekhGZjnEchBnS BVmwMvnRNXO3ylGxTC6TDcM8SJlq1Ey1OtgcoSaCnHHaItEEWwG5gTUFNTtvROl3UvutY+ZAs3GywGG4Rdp70bzQSB8zZ8ifq43xCnLP89g5K4WsoXUAIGJy iYZTEa2vOHdA57OK21m9xHuLfIWmwJDEJLCoQQa3rf7n3bw0iH/YvP+LMpt99heAvhKrWTz0uzxpgbupzziIv86BNsXfkQ== Sender: stable-owner@vger.kernel.org X-Mailing-List: stable@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On 4/18/2018 9:08 AM, David Laight wrote: > From: Tom Talpey >> Sent: 18 April 2018 12:32 > ... >> On 4/17/2018 8:33 PM, Long Li wrote: >>> From: Long Li >>> >>> 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). Memory registration does not requires pages to be physically contiguous. RDMA Regions can and do support very large physical page scatter/gather, and the adapter DMA's them readily. Is this the only reason? Tom.