Re: [PATCH v3 0/2] rust: page: Add support for existing struct page mappings

[Matthew Wilcox]

On Fri, Nov 22, 2024 at 01:18:28AM +0200, Abdiel Janulgue wrote:
> We need an abstraction of struct page to construct a scatterlist which is
> needed for an internal firmware structure. Now most of pages needed there
> come from vmalloc_to_page() which, unlike the current rust Page abstraction,
> not allocated on demand but is an existing mapping.
> 
> Hope that clears things up!

That's very helpful!  So the lifetime of the scatterllist must not
outlive the lifetime of the vmalloc allocation.  That means you can call
kmap_local_page() on the page in the scatterlist without worrying about
the refcount of the struct page.  BTW, you can't call page_address() on
vmalloc memory because vmalloc can allocate pages from HIGHMEM.  Unless
you're willing to disable support for 32-bit systems with highmem ...