linux-kernel - Re: [PATCH for-next 2/4] RDMA/hns: Add IOMMU enable support in hip08

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Date:   Tue, 7 Nov 2017 07:58:05 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     Jason Gunthorpe <jgg@...pe.ca>
Cc:     "Wei Hu (Xavier)" <xavier.huwei@...wei.com>,
        Robin Murphy <robin.murphy@....com>,
        Leon Romanovsky <leon@...nel.org>, shaobo.xu@...el.com,
        xavier.huwei@....com, lijun_nudt@....com, oulijun@...wei.com,
        linux-rdma@...r.kernel.org, charles.chenxin@...wei.com,
        linuxarm@...wei.com, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        dledford@...hat.com, liuyixian@...wei.com, zhangxiping3@...wei.com,
        shaoboxu@....com
Subject: Re: [PATCH for-next 2/4] RDMA/hns: Add IOMMU enable support in hip08

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.