linux-kernel - Re: [PATCH 3/5] hyperv/IOMMU: Enable swiotlb bounce buffer for Isolation VM

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Message-ID: <f7fcb4d5-fcdd-0d24-60ed-62c27ed8e2d9@gmail.com>
Date:   Fri, 19 Nov 2021 22:23:45 +0800
From:   Tianyu Lan <ltykernel@...il.com>
To:     Christoph Hellwig <hch@....de>
Cc:     dave.hansen@...ux.intel.com, luto@...nel.org, peterz@...radead.org,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, x86@...nel.org,
        hpa@...or.com, jgross@...e.com, sstabellini@...nel.org,
        boris.ostrovsky@...cle.com, kys@...rosoft.com,
        haiyangz@...rosoft.com, sthemmin@...rosoft.com, wei.liu@...nel.org,
        decui@...rosoft.com, joro@...tes.org, will@...nel.org,
        davem@...emloft.net, kuba@...nel.org, jejb@...ux.ibm.com,
        martin.petersen@...cle.com, m.szyprowski@...sung.com,
        robin.murphy@....com, xen-devel@...ts.xenproject.org,
        michael.h.kelley@...rosoft.com,
        Tianyu Lan <Tianyu.Lan@...rosoft.com>,
        iommu@...ts.linux-foundation.org, linux-hyperv@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org,
        netdev@...r.kernel.org, vkuznets@...hat.com, brijesh.singh@....com,
        konrad.wilk@...cle.com, parri.andrea@...il.com,
        thomas.lendacky@....com, dave.hansen@...el.com
Subject: Re: [PATCH 3/5] hyperv/IOMMU: Enable swiotlb bounce buffer for
 Isolation VM

On 11/17/2021 10:00 PM, Tianyu Lan wrote:
> On 11/17/2021 6:01 PM, Christoph Hellwig wrote:
>> This doesn't really have much to do with normal DMA mapping,
>> so why does this direct through the dma ops?
>>
> 
> According to the previous discussion, dma_alloc_noncontigous()
> and dma_vmap_noncontiguous() may be used to handle the noncontigous
> memory alloc/map in the netvsc driver. So add alloc/free and vmap/vunmap
> callbacks here to handle the case. The previous patch v4 & v5 handles
> the allocation and map in the netvsc driver. If this should not go 
> though dma ops, We also may make it as vmbus specific function and keep
> the function in the vmbus driver.
> 
> https://lkml.org/lkml/2021/9/28/51


Hi Christoph:
       Sorry to bother you. Could you have a look? Which solution do you
prefer? If we need to call dma_alloc/map_noncontigous() function in the
netvsc driver what patch 4 does. The Hyper-V specific implementation
needs to be hided in some callbacks and call these callback in the
dma_alloc/map_noncontigous(). I used dma ops here. If the allocation and
map operation should be Hyper-V specific function, we may put these
functions in the vmbus driver and other vmbus device drivers also may
reuse these functions if necessary.

Thanks.