linux-kernel - Re: [PATCH v6 12/18] arm64/mm: Wire up PTE

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Date: Tue, 20 Feb 2024 20:50:37 +0100
From: Ryan Roberts <ryan.roberts@....com>
To: John Hubbard <jhubbard@...dia.com>,
 Catalin Marinas <catalin.marinas@....com>
Cc: Will Deacon <will@...nel.org>, Ard Biesheuvel <ardb@...nel.org>,
 Marc Zyngier <maz@...nel.org>, James Morse <james.morse@....com>,
 Andrey Ryabinin <ryabinin.a.a@...il.com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Matthew Wilcox <willy@...radead.org>, Mark Rutland <mark.rutland@....com>,
 David Hildenbrand <david@...hat.com>,
 Kefeng Wang <wangkefeng.wang@...wei.com>, Zi Yan <ziy@...dia.com>,
 Barry Song <21cnbao@...il.com>, Alistair Popple <apopple@...dia.com>,
 Yang Shi <shy828301@...il.com>, Thomas Gleixner <tglx@...utronix.de>,
 Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
 Dave Hansen <dave.hansen@...ux.intel.com>, "H. Peter Anvin" <hpa@...or.com>,
 linux-arm-kernel@...ts.infradead.org, x86@...nel.org,
 linuxppc-dev@...ts.ozlabs.org, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 12/18] arm64/mm: Wire up PTE_CONT for user mappings

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,