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

[Jason Gunthorpe]

On Tue, Feb 04, 2025 at 09:41:29PM +0100, David Hildenbrand wrote:
> On 04.02.25 21:26, Jason Gunthorpe wrote:
> > On Tue, Feb 04, 2025 at 09:05:47PM +0100, David Hildenbrand wrote:
> > > Fully agreed, this is going into the right direction. Dumping what's mapped
> > > is a different story. Maybe that dumping logic could simply be written in C
> > > for the time being?
> > 
> > ?
> > 
> > Isn't dumping just a
> >    decode pte -> phys_to_virt() -> for_each_u64(virt) -> printk?
> > 
> 
> IIUC, the problematic bit is that you might not have a directmap such that
> phys_to_virt() would tell you the whole story.

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.

The leaf pages could be anything and you should enver phys_to_virt
those, this is what I mean by:

> > Or do you mean trying to decode the leaf entires into some struct page
> > detail? Does a GPU need to do that? Agree that would be better as some
> > C function to take in a KVA instead of a struct page and populate a
> > string with details about that KVA from the struct page.

Though I should have said phys_addr_t not KVA

Jason