Re: [PATCH 0/6] rust: page: Support borrowing `struct page` and physaddr conversion

[David Hildenbrand]

On 06.02.25 00:17, Matthew Wilcox wrote:
> On Tue, Feb 04, 2025 at 04:49:47PM -0400, Jason Gunthorpe wrote:
> > The phys_to_virt() I mean is on the page table pages themselves, not
> > on a leaf.
> >
> > All page table pages came from alloc_pages_node() and you'd do
> > virt_to_phys() to stick them into a next-table PTE, then
> > phys_to_virt() to bring them back:
> >
> >    phys_to_virt(virt_to_phys(page_address(alloc_pages_node())))
> >
> > Effectively.
>
> except for s390 & ppc where the page table can be smaller than
> PAGE_SIZE, so you really only have a physical address that can be
> converted to a virtual address.

I recall in the context of IOMMU page tables we don't perform this 
packing. So what you say is certainly true for process page tables, but 
likely not for IOMMU etc in the context of this series.

--
Cheers,

David / dhildenb