linux-kernel - Re: [RFT][PATCH v1 6/6] vfio: Replace phys_pfn with phys_page for vfio_pin

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Date:   Fri, 17 Jun 2022 01:54:05 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Nicolin Chen <nicolinc@...dia.com>
Cc:     kwankhede@...dia.com, corbet@....net, hca@...ux.ibm.com,
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Subject: Re: [RFT][PATCH v1 6/6] vfio: Replace phys_pfn with phys_page for
 vfio_pin_pages()

There is a bunch of code an comments in the iommu type1 code that
suggest we can pin memory that is not page backed.  

>  int vfio_pin_pages(struct vfio_device *device, dma_addr_t iova,
> +		   int npage, int prot, struct page **phys_page)

I don't think phys_page makes much sense as an argument name.
I'd just call this pages.

> +			phys_page[i] = pfn_to_page(vpfn->pfn);

Please store the actual page pointer in the vfio_pfn structure.

>  		remote_vaddr = dma->vaddr + (iova - dma->iova);
> -		ret = vfio_pin_page_external(dma, remote_vaddr, &phys_pfn[i],
> +		ret = vfio_pin_page_external(dma, remote_vaddr, &phys_pfn,
>  					     do_accounting);

Please just return the actual page from vaddr_get_pfns through
vfio_pin_pages_remote and vfio_pin_page_external, maybe even as a prep
patch as that is a fair amount of churn.