On 14.10.24 16:25, Gregory Price wrote:
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.
Right, at least the EXPORT is not required.
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?
Let's summarize what we currently have on x86 is:
1) probe_memory_block_size()
Triggered on first memory_block_size_bytes() invocation. Makes a
decision based on:
a) Already set size using set_memory_block_size_order()
b) RAM size
c) Bare metal vs. virt (bare metal -> use max)
d) Virt: largest block size aligned to memory end
2) set_memory_block_size_order()
Triggered by set_block_size() on UV systems.
I don't think set_memory_block_size_order() is the right tool to use. We
just want to leave that alone I think -- it's a direct translation of a
kernel cmdline parameter that should win.
You essentially want to tweak the b)->d) logic to take other alignment
into consideration.
Maybe have some simple callback mechanism probe_memory_block_size() that
can consult other sources for alignment requirements?
If that's not an option, then another way to set further min-alignment
requirements (whereby we take MIN(old_align, new_align))?
--
Cheers,
David / dhildenb
