netdev - Re: [PATCH V3 11/13] HV/IOMMU: Enable swiotlb bounce buffer for Isolation VM

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Date:   Fri, 20 Aug 2021 06:13:40 +0200
From:   "hch@....de" <hch@....de>
To:     Michael Kelley <mikelley@...rosoft.com>
Cc:     Tianyu Lan <ltykernel@...il.com>,
        KY Srinivasan <kys@...rosoft.com>,
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Subject: Re: [PATCH V3 11/13] HV/IOMMU: Enable swiotlb bounce buffer for
 Isolation VM

On Thu, Aug 19, 2021 at 06:11:30PM +0000, Michael Kelley wrote:
> This function is manipulating page tables in the guest VM.  It is not involved
> in communicating with Hyper-V, or passing PFNs to Hyper-V.  The pfn array
> contains guest PFNs, not Hyper-V PFNs.  So it should use PAGE_SIZE
> instead of HV_HYP_PAGE_SIZE, and similarly PAGE_SHIFT and virt_to_pfn().
> If this code were ever to run on ARM64 in the future with PAGE_SIZE other
> than 4 Kbytes, the use of PAGE_SIZE is correct choice.

Yes.  I just stumled over this yesterday.  I think we can actually use a
nicer helper ased around vmap_range() to simplify this exactly because it
always uses the host page size.  I hope I can draft up a RFC today.