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

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Message-ID: <20220620030046.GB5219@nvidia.com>
Date:   Mon, 20 Jun 2022 00:00:46 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Nicolin Chen <nicolinc@...dia.com>, kwankhede@...dia.com,
        corbet@....net, hca@...ux.ibm.com, gor@...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()

On Fri, Jun 17, 2022 at 01:54:05AM -0700, Christoph Hellwig wrote:
> There is a bunch of code an comments in the iommu type1 code that
> suggest we can pin memory that is not page backed.  

AFAIK you can.. The whole follow_pte() mechanism allows raw PFNs to be
loaded into the type1 maps and the pin API will happily return
them. This happens in almost every qemu scenario because PCI MMIO BAR
memory ends up routed down this path.

Thanks,
Jason