On Fri, Feb 16, 2024 at 12:53:43PM +0000, Ryan Roberts wrote: > On 16/02/2024 12:25, Catalin Marinas wrote: > > On Thu, Feb 15, 2024 at 10:31:59AM +0000, Ryan Roberts wrote: > >> arch/arm64/mm/contpte.c | 285 +++++++++++++++++++++++++++++++ > > > > Nitpick: I think most symbols in contpte.c can be EXPORT_SYMBOL_GPL(). > > We don't expect them to be used by random out of tree modules. In fact, > > do we expect them to end up in modules at all? Most seem to be called > > from the core mm code. > > 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@xxxxxxx/#t > > So they definitely need to be exported. Perhaps we can tighten it to > 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. 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). > > If you can make this easier to parse (in a few years time) with an > > additional patch adding some more comments, that would be great. For > > this patch: > > I already have a big block comment at the top, which was trying to explain it. > Clearly not well enough though. I'll add more comments as a follow up patch when > I get back from holiday. I read that comment but it wasn't immediately obvious what the atomicity requirements are - basically we require a single PTE to be atomically read (which it is), the rest is the dirty/young state being added on top. I guess a sentence along these lines would do. Enjoy your holiday! -- Catalin
