Subject: Re: [RFC PATCH V3 10/11] HV/Netvsc: Add Isolation VM support for netvsc driver

From: Christoph Hellwig <[email-masked]>
Date: Mon, 14 Jun 2021 09:09:03 +0200

On Mon, Jun 07, 2021 at 11:21:20PM +0800, Tianyu Lan wrote:
>> dma_map_single can only be used on page baked memory, and if this is
>> using page backed memory you wouldn't need to do thee phys_to_virt
>> tricks.  Can someone explain the mess here in more detail?
>
> Sorry. Could you elaborate the issue? These pages in the pb array are not 
> allocated by DMA API and using dma_map_single() here is to map these pages' 
> address to bounce buffer physical address.

dma_map_single just calls dma_map_page using virt_to_page.  So this
can't work on addresses not in the kernel linear mapping.