linux-kernel - Re: [PATCH V3 13/13] HV/Storvsc: Add Isolation VM support for storvsc driver

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Message-ID: <9ae704a9-838c-0a54-9c16-f0f10eaaaefe@gmail.com>
Date:   Fri, 20 Aug 2021 23:37:56 +0800
From:   Tianyu Lan <ltykernel@...il.com>
To:     Michael Kelley <mikelley@...rosoft.com>,
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Subject: Re: [PATCH V3 13/13] HV/Storvsc: Add Isolation VM support for storvsc
 driver

On 8/20/2021 11:20 PM, Tianyu Lan wrote:
>> The whole approach here is to do dma remapping on each individual page
>> of the I/O buffer.  But wouldn't it be possible to use dma_map_sg() to 
>> map
>> each scatterlist entry as a unit?  Each scatterlist entry describes a 
>> range of
>> physically contiguous memory.  After dma_map_sg(), the resulting dma
>> address must also refer to a physically contiguous range in the swiotlb
>> bounce buffer memory.   So at the top of the "for" loop over the 
>> scatterlist
>> entries, do dma_map_sg() if we're in an isolated VM.  Then compute the
>> hvpfn value based on the dma address instead of sg_page().  But 
>> everything
>> else is the same, and the inner loop for populating the pfn_arry is 
>> unmodified.
>> Furthermore, the dma_range array that you've added is not needed, since
>> scatterlist entries already have a dma_address field for saving the 
>> mapped
>> address, and dma_unmap_sg() uses that field.
> 
> I don't use dma_map_sg() here in order to avoid introducing one more 
> loop(e,g dma_map_sg()). We already have a loop to populate 
> cmd_request->dma_range[] and so do the dma map in the same loop.

Sorry for a typo. s/cmd_request->dma_range[]/payload->range.pfn_array[]/