Re: [PATCH v6 12/18] arm64/mm: Wire up PTE_CONT for user mappings

[Ryan Roberts <ryan.roberts@arm.com>]

On 16/02/2024 19:54, John Hubbard wrote:
> On 2/16/24 08:56, Catalin Marinas wrote:
> ...
>>> The problem is that the contpte_* symbols are called from the ptep_* inline
>>> functions. So where those inlines are called from modules, we need to make sure
>>> the contpte_* symbols are available.
>>>
>>> John Hubbard originally reported this problem against v1 and I enumerated all
>>> the drivers that call into the ptep_* inlines here:
>>> https://lore.kernel.org/linux-arm-kernel/b994ff89-1a1f-26ca-9479-b08c77f94be8@arm.com/#t
>>>
>>> So they definitely need to be exported. Perhaps we can tighten it to
> 
> Yes. Let's keep the in-tree modules working.
> 
>>> EXPORT_SYMBOL_GPL(), but I was being cautious as I didn't want to break anything
>>> out-of-tree. I'm not sure what the normal policy is? arm64 seems to use ~equal
>>> amounts of both.
> 
> EXPORT_SYMBOL_GPL() seems appropriate and low risk. As Catalin says below,
> these really are deeply core mm routines, and any module operating at this
> level is not going to be able to survive on EXPORT_SYMBOL alone, IMHO.
> 
> Now, if only I could find an out of tree module to test that claim on... :)
> 
> 
>> I don't think we are consistent here. For example set_pte_at() can't be
>> called from non-GPL modules because of __sync_icache_dcache. OTOH, such
>> driver is probably doing something dodgy. Same with
>> apply_to_page_range(), it's GPL-only (called from i915).
>>
>> Let's see if others have any view over the next week or so, otherwise
>> I'd go for _GPL and relax it later if someone has a good use-case (can
>> be a patch on top adding _GPL).
> 
> I think going directly to _GPL for these is fine, actually.

OK I'll send out a patch to convert these to _GPL on my return on Monday.
Hopefully Andrew will be able to squash the patch into the existing series.

> 
> 
> thanks,