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Subject: Re: [PATCH 13/13] HV/Storvsc: Add Isolation VM support for storvsc
 driver
To:     Joerg Roedel <joro@8bytes.org>
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References: <20210728145232.285861-1-ltykernel@gmail.com>
 <20210728145232.285861-14-ltykernel@gmail.com> <YQfxA/AYfOqyqNh0@8bytes.org>
From:   Tianyu Lan <ltykernel@gmail.com>
Message-ID: <eaeb75b7-7e98-ad2d-0e2c-0565b9db79dd@gmail.com>
Date:   Mon, 2 Aug 2021 22:08:43 +0800
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On 8/2/2021 9:20 PM, Joerg Roedel wrote:
> On Wed, Jul 28, 2021 at 10:52:28AM -0400, Tianyu Lan wrote:
>> In Isolation VM, all shared memory with host needs to mark visible
>> to host via hvcall. vmbus_establish_gpadl() has already done it for
>> storvsc rx/tx ring buffer. The page buffer used by vmbus_sendpacket_
>> mpb_desc() still need to handle. Use DMA API to map/umap these
>> memory during sending/receiving packet and Hyper-V DMA ops callback
>> will use swiotlb function to allocate bounce buffer and copy data
>> from/to bounce buffer.
> 
> I am wondering why you dont't use DMA-API unconditionally? It provides
> enough abstraction to do the right thing for isolated and legacy VMs.
> 

In VMbus, there is already a similar bounce buffer design and so there 
is no need to call DMA-API for such buffer. Calling DMA-API is to use
swiotlb bounce buffer for those buffer which hasn't been covered. This
is why need to conditionally call DMA API.