Re: [PATCH RFC v9 13/25] mm: kpkeys: Introduce early page table allocator

["David Hildenbrand (Arm)" <david@kernel.org>]

On 8/18/26 16:08, Kevin Brodsky wrote:
> The kpkeys_hardened_pgtables feature aims to protect all page table
> pages (PTPs) by mapping them with a privileged pkey. This is primarily
> handled by kpkeys_pgtable_alloc(), called from pagetable_alloc().
> However, this does not cover PTPs allocated early, before the
> buddy allocator is available. These PTPs are allocated by architecture
> code, either 1. from static pools or 2. using the memblock allocator,
> and should also be protected.
> 
> This patch addresses the second category: PTPs allocated via memblock.
> Such PTPs are notably used to create the linear map. Protecting them as
> soon as they are allocated would require modifying the linear map while
> it is being created, which seems at best difficult. Instead, a
> simple allocator is introduced, obtaining pages from memblock and
> keeping track of all allocated ranges to set their pkey once it is
> safe to do so. PTPs allocated at that stage are not freed, so there
> is no need to manage a free list.

I'm think of ways to avoid remembering these ranges. I guess we get called that
early that we don't even have a ptdesc where we could just link the pages.

If only page tables would be linked in some datastructure where we could find
them all ... ;)

... why can't we just scan the page table hierarchy to find all page tables that
need protection?

-- 
Cheers,

David