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Date: Tue, 7 Nov 2017 07:58:05 -0800
From: Christoph Hellwig <hch@infradead.org>
Subject: Re: [PATCH for-next 2/4] RDMA/hns: Add IOMMU enable support in hip08
Message-ID: <20171107155805.GA24082@infradead.org>
References: <1506763741-81429-1-git-send-email-xavier.huwei@huawei.com>
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Sender: owner-linux-mm@kvack.org
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To: Jason Gunthorpe <jgg@ziepe.ca>
Cc: "Wei Hu (Xavier)" <xavier.huwei@huawei.com>, Robin Murphy <robin.murphy@arm.com>, Leon Romanovsky <leon@kernel.org>, shaobo.xu@intel.com, xavier.huwei@tom.com, lijun_nudt@163.com, oulijun@huawei.com, linux-rdma@vger.kernel.org, charles.chenxin@huawei.com, linuxarm@huawei.com, iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, dledford@redhat.com, liuyixian@huawei.com, zhangxiping3@huawei.com, shaoboxu@tom.com

On Tue, Nov 07, 2017 at 08:48:38AM -0700, Jason Gunthorpe wrote:
> Can't you just use vmalloc and dma_map that? Other drivers follow that
> approach..

You can't easily due to the flushing requirements.  We used to do that
in XFS and it led to problems.  You need the page allocator + vmap +
invalidate_kernel_vmap_range + flush_kernel_vmap_range to get the
cache flushing right.

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