On Sun, Jul 13, 2025 at 08:56:10PM +0300, Mike Rapoport wrote:
On Sun, Jul 13, 2025 at 08:39:53PM +0900, Harry Yoo wrote:
On Fri, Jul 11, 2025 at 06:18:44PM +0200, David Hildenbrand wrote:
population helpers that invoke architecture-specific hooks to properly synchronize the page tables.
I was expecting to see the sync be done in common code -- such that it cannot be missed :)
You mean something like an arch-independent implementation of sync_global_pgds()?
That would be a "much more robust" approach ;)
To do that, the kernel would need to maintain a list of page tables that have kernel portion mapped and perform the sync in the common code.
But determining which page tables to add to the list would be highly architecture-specific. For example, I think some architectures use separate page tables for kernel space, unlike x86 (e.g., arm64 TTBR1, SPARC) and user page tables should not be affected.
sync_global_pgds() can be still implemented per architecture, but it can be called from the common code.
A good point, and that can be done!
Actually, that was the initial plan and I somehow thought that you can't determine if the architecture is using 5-level or 4-level paging and decide whether to call arch_sync_kernel_pagetables(). But looking at how it's done in vmalloc, I think it can be done in a similar way.
We already have something like that for vmalloc that calls arch_sync_kernel_mappings(). It's implemented only by x86-32 and arm, other architectures do not define it.
It is indeed a good example and was helpful. Thank you for the comment, Mike!
-- Sincerely yours, Mike.