On 28/03/2018 12:16, David Rientjes wrote: > On Wed, 28 Mar 2018, Laurent Dufour wrote: > >>>> This configuration variable will be used to build the code needed to >>>> handle speculative page fault. >>>> >>>> By default it is turned off, and activated depending on architecture >>>> support. >>>> >>>> Suggested-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> >>>> Signed-off-by: Laurent Dufour <ldufour@xxxxxxxxxxxxxxxxxx> >>>> --- >>>> mm/Kconfig | 3 +++ >>>> 1 file changed, 3 insertions(+) >>>> >>>> diff --git a/mm/Kconfig b/mm/Kconfig >>>> index abefa573bcd8..07c566c88faf 100644 >>>> --- a/mm/Kconfig >>>> +++ b/mm/Kconfig >>>> @@ -759,3 +759,6 @@ config GUP_BENCHMARK >>>> performance of get_user_pages_fast(). >>>> >>>> See tools/testing/selftests/vm/gup_benchmark.c >>>> + >>>> +config SPECULATIVE_PAGE_FAULT >>>> + bool >>> >>> Should this be configurable even if the arch supports it? >> >> Actually, this is not configurable unless by manually editing the .config file. >> >> I made it this way on the Thomas's request : >> https://lkml.org/lkml/2018/1/15/969 >> >> That sounds to be the smarter way to achieve that, isn't it ? >> > > Putting this in mm/Kconfig is definitely the right way to go about it > instead of any generic option in arch/*. > > My question, though, was making this configurable by the user: > > config SPECULATIVE_PAGE_FAULT > bool "Speculative page faults" > depends on X86_64 || PPC > default y > help > .. > > It's a question about whether we want this always enabled on x86_64 and > power or whether the user should be able to disable it (right now they > can't). With a large feature like this, you may want to offer something > simple (disable CONFIG_SPECULATIVE_PAGE_FAULT) if someone runs into > regressions. I agree, but I think it would be important to get the per architecture enablement to avoid complex check here. For instance in the case of powerPC this is only supported for PPC_BOOK3S_64. To avoid exposing such per architecture define here, what do you think about having supporting architectures setting ARCH_SUPPORTS_SPECULATIVE_PAGE_FAULT and the SPECULATIVE_PAGE_FAULT depends on this, like this: In mm/Kconfig: config SPECULATIVE_PAGE_FAULT bool "Speculative page faults" depends on ARCH_SUPPORTS_SPECULATIVE_PAGE_FAULT && SMP default y help ... In arch/powerpc/Kconfig: config PPC ... select ARCH_SUPPORTS_SPECULATIVE_PAGE_FAULT if PPC_BOOK3S_64 In arch/x86/Kconfig: config X86_64 ... select ARCH_SUPPORTS_SPECULATIVE_PAGE_FAULT
