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If this is wrong, there is no advantages this changes.. >>> I don't know what the dmabuf folks did, but yes, it is wrong. >>> >>> IOMEM must be touched using only special accessors, some platforms >>> crash if you don't do this. Even x86 will crash if you touch it with >>> something like an XMM optimized memcpy. >>> >>> Christian? If the vmap succeeds what rules must the caller use to >>> access the memory? >> See dma-buf-map.h and especially struct dma_buf_map. >> >> MMIO memory is perfectly supported here and actually the most common case. > Okay that looks sane, but this rxe RFC seems to ignore this > completely. It stuffs the vaddr directly into a umem which goes to all > manner of places in the driver. > > ?? Well, yes that can go boom pretty quickly. Not sure what they want to use this for. 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header.from=amd.com; Received: from MWHPR1201MB0192.namprd12.prod.outlook.com (2603:10b6:301:5a::14) by MWHPR12MB1453.namprd12.prod.outlook.com (2603:10b6:301:e::22) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4755.16; Fri, 10 Dec 2021 13:29:00 +0000 Received: from MWHPR1201MB0192.namprd12.prod.outlook.com ([fe80::d16c:a6d5:5d2e:f9d4]) by MWHPR1201MB0192.namprd12.prod.outlook.com ([fe80::d16c:a6d5:5d2e:f9d4%12]) with mapi id 15.20.4755.027; Fri, 10 Dec 2021 13:29:00 +0000 Subject: Re: [RFC PATCH v4 0/2] RDMA/rxe: Add dma-buf support To: Jason Gunthorpe References: <20211122110817.33319-1-mie@igel.co.jp> <20211207171447.GA6467@ziepe.ca> <20211210124204.GG6467@ziepe.ca> <880e25ad-4fe9-eacd-a971-993eaea37fc4@amd.com> <20211210132656.GH6467@ziepe.ca> From: =?UTF-8?Q?Christian_K=c3=b6nig?= Message-ID: Date: Fri, 10 Dec 2021 14:28:50 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.14.0 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Hayama , Leon Romanovsky , linux-rdma , Daniel Vetter , Linux Kernel Mailing List , dri-devel@lists.freedesktop.org, Tomohito Esaki , linaro-mm-sig@lists.linaro.org, Doug Ledford , Zhu Yanjun , Shunsuke Mie , Alex Deucher , Sean Hefty , Maor Gottlieb , Jianxin Xiong , linux-media@vger.kernel.org Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" Am 10.12.21 um 14:26 schrieb Jason Gunthorpe: > On Fri, Dec 10, 2021 at 01:47:37PM +0100, Christian König wrote: >> Am 10.12.21 um 13:42 schrieb Jason Gunthorpe: >>> On Fri, Dec 10, 2021 at 08:29:24PM +0900, Shunsuke Mie wrote: >>>> Hi Jason, >>>> Thank you for replying. >>>> >>>> 2021年12月8日(水) 2:14 Jason Gunthorpe : >>>>> On Fri, Dec 03, 2021 at 12:51:44PM +0900, Shunsuke Mie wrote: >>>>>> Hi maintainers, >>>>>> >>>>>> Could you please review this patch series? >>>>> Why is it RFC? >>>>> >>>>> I'm confused why this is useful? >>>>> >>>>> This can't do copy from MMIO memory, so it shouldn't be compatible >>>>> with things like Gaudi - does something prevent this? >>>> I think if an export of the dma-buf supports vmap, CPU is able to access the >>>> mmio memory. >>>> >>>> Is it wrong? If this is wrong, there is no advantages this changes.. >>> I don't know what the dmabuf folks did, but yes, it is wrong. >>> >>> IOMEM must be touched using only special accessors, some platforms >>> crash if you don't do this. Even x86 will crash if you touch it with >>> something like an XMM optimized memcpy. >>> >>> Christian? If the vmap succeeds what rules must the caller use to >>> access the memory? >> See dma-buf-map.h and especially struct dma_buf_map. >> >> MMIO memory is perfectly supported here and actually the most common case. > Okay that looks sane, but this rxe RFC seems to ignore this > completely. It stuffs the vaddr directly into a umem which goes to all > manner of places in the driver. > > ?? Well, yes that can go boom pretty quickly. Not sure what they want to use this for. Christian. > > Jason