Re: [RFT][PATCH v1 6/6] vfio: Replace phys_pfn with phys_page for vfio_pin_pages()

Christoph Hellwig
2022-06-19T06:18:32Z

On Fri, Jun 17, 2022 at 03:06:25PM -0700, Nicolin Chen wrote:
> 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.
>
> Would you mind explaining the use case for pinning memory that
> isn't page backed? And do we have such use case so far?

Sorry, I should have deleted that sentence. I wrote it before spending
some more time to dig through the code and all the locked memory has
page backing. There just seem to be a lot of checks left inbetween
if a pfn is page backed, mostly due to the pfn based calling convetions.

> I can do that. I tried once, but there were just too much changes
> inside type1 code that felt like a chain reaction. If we plan to
> eventually replace with IOMMUFD implementations, these changes in
> type1 might not be necessary, I thought.

To make sure we keep full compatibility I suspect the final iommufd
implementation has to be gradutally created from the existing code
anyway.