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[121.45.221.81]) by smtp.gmail.com with ESMTPSA id a185sm15138421pfa.27.2020.03.23.20.38.01 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 23 Mar 2020 20:38:05 -0700 (PDT) Subject: Re: [PATCH 1/2] dma-mapping: add a dma_ops_bypass flag to struct device To: Christoph Hellwig Cc: iommu@lists.linux-foundation.org, linuxppc-dev@lists.ozlabs.org, Lu Baolu , Greg Kroah-Hartman , Joerg Roedel , Robin Murphy , linux-kernel@vger.kernel.org, "Aneesh Kumar K.V" References: <20200320141640.366360-1-hch@lst.de> <20200320141640.366360-2-hch@lst.de> <2f31d0dd-aa7e-8b76-c8a1-5759fda5afc9@ozlabs.ru> <20200323083705.GA31245@lst.de> <37ce1b7e-264d-292d-32b1-093b24b3525c@ozlabs.ru> <20200323172014.GA31269@lst.de> From: Alexey Kardashevskiy Autocrypt: addr=aik@ozlabs.ru; keydata= mQINBE+rT0sBEADFEI2UtPRsLLvnRf+tI9nA8T91+jDK3NLkqV+2DKHkTGPP5qzDZpRSH6mD EePO1JqpVuIow/wGud9xaPA5uvuVgRS1q7RU8otD+7VLDFzPRiRE4Jfr2CW89Ox6BF+q5ZPV 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Zd44XWqUu7FzVOYaSgIvTP0hNrBYm/E6M7yrLbs3JY74fGzPWGRbBUHTZXQEqQnZglXaVB5V ZhSFtHopZnBSCUSNDbB+QGy4B/E++Bb02IBTGl/JxmOwG+kZUnymsPvTtnNIeTLHxN/H/ae0 c7E5M+/NpslPCmYnDjs5qg0/3ihh6XuOGggZQOqrYPC3PnsNs3NxirwOkVPQgO6mXxpuifvJ DG9EMkK8IBXnLulqVk54kf7fE0jT/d8RTtJIA92GzsgdK2rpT1MBKKVffjRFGwN7nQVOzi4T XrB5p+6ML7Bd84xOEGsj/vdaXmz1esuH7BOZAGEZfLRCHJ0GVCSssg== Message-ID: Date: Tue, 24 Mar 2020 14:37:59 +1100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <20200323172014.GA31269@lst.de> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 24/03/2020 04:20, Christoph Hellwig wrote: > On Mon, Mar 23, 2020 at 07:58:01PM +1100, Alexey Kardashevskiy wrote: >>>> 0x100.0000.0000 .. 0x101.0000.0000 >>>> >>>> 2x4G, each is 1TB aligned. And we can map directly only the first 4GB >>>> (because of the maximum IOMMU table size) but not the other. And 1:1 on >>>> that "pseries" is done with offset=0x0800.0000.0000.0000. >>>> >>>> So we want to check every bus address against dev->bus_dma_limit, not >>>> dev->coherent_dma_mask. In the example above I'd set bus_dma_limit to >>>> 0x0800.0001.0000.0000 and 1:1 mapping for the second 4GB would not be >>>> tried. Does this sound reasonable? Thanks, >>> >>> bus_dma_limit is just another limiting factor applied on top of >>> coherent_dma_mask or dma_mask respectively. >> >> This is not enough for the task: in my example, I'd set bus limit to >> 0x0800.0001.0000.0000 but this would disable bypass for all RAM >> addresses - the first and the second 4GB blocks. > > So what about something like the version here: > > http://git.infradead.org/users/hch/misc.git/shortlog/refs/heads/dma-bypass.3 dma_alloc_direct() and dma_map_direct() do the same thing now which is good, did I miss anything else? This lets us disable bypass automatically if this weird memory appears in the system but does not let us have 1:1 after that even for normal RAM. Thanks, -- Alexey