On Mon, Oct 14, 2024 at 01:54:27PM +0200, David Hildenbrand wrote: > On 08.10.24 17:21, Gregory Price wrote: > > On Tue, Oct 08, 2024 at 05:02:33PM +0200, David Hildenbrand wrote: > > > On 08.10.24 16:51, Gregory Price wrote: > > > > > > +int __weak set_memory_block_size_order(unsigned int order) > > > > > > +{ > > > > > > + return -ENODEV; > > > > > > +} > > > > > > +EXPORT_SYMBOL_GPL(set_memory_block_size_order); > > > > > > > > > > I can understand what you are trying to achieve, but letting arbitrary > > > > > modules mess with this sounds like a bad idea. > > > > > > > > > > > > > I suppose the alternative is trying to scan the CEDT from inside each > > > > machine, rather than the ACPI driver? Seems less maintainable. > > > > > > > > I don't entirely disagree with your comment. I hummed and hawwed over > > > > externing this - hence the warning in the x86 machine. > > > > > > > > Open to better answers. > > > > > > Maybe an interface to add more restrictions on the maximum size might be > > > better (instead of setting the size/order, you would impose another upper > > > limit). > > > > That is effectively what set_memory_block_size_order is, though. Once > > blocks are exposed to the allocators, its no longer safe to change the > > size (in part because it was built assuming it wouldn't change, but I > > imagine there are other dragons waiting in the shadows to bite me). > > Yes, we must run very early. > > How is this supposed to interact with code like > > set_block_size() > > that also calls set_memory_block_size_order() on UV systems (assuming there > will be CXL support sooner or later?)? > > Tying the other email to this one - just clarifying the way forward here. It sounds like you're saying at a minimum drop EXPORT tags to prevent modules from calling it - but it also sounds like built-ins need to be prevented from touching it as well after a certain point in early boot. Do you think I should go down the advise() path as suggested by Ira, just adding a arch_lock_blocksize() bit and have set_..._order check it, or should we just move towards each architecture having to go through the ACPI:CEDT itself? Doesn't sound like we've quite hit a consensus on where the actual adjustment logic should land - just that this shouldn't be touched by modules. ~Gregory