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

[Tianyu Lan]

On 11/26/2021 3:40 PM, Christoph Hellwig wrote:
> On Wed, Nov 17, 2021 at 10:00:08PM +0800, 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.
>
> But that only makes sense if they can actually use the normal DMA ops.
> If you implement your own incomplete ops and require to use them you
> do nothing but adding indirect calls to your fast path and making the
> code convoluted.

Because the generic part implementation can't meet the netvsc driver
requests that allocate 16M memory and map pages via vmap_pfn(). So add 
Hyperv alloc_noncontiguous and vmap_noncontiguous callbacks. If this is
not a right way. we should call these hyper-V functions in the netvsc
driver directly, right?

Could you have a look at Michael summary about this series we made and
give some guides?

https://www.mail-archive.com/xen-devel@xxxxxxxxxxxxxxxxxxxx/msg109284.html

Thanks.