Re: [PATCH] mm/execmem: Make ARCH_WANTS_EXECMEM_LATE depend on EXECMEM

[Catalin Marinas <catalin.marinas@arm.com>]

On Mon, Dec 09, 2024 at 07:43:32PM +0530, Anshuman Khandual wrote:
> On 12/9/24 18:06, kernel test robot wrote:
> > kernel test robot noticed the following build warnings:
> > 
> > [auto build test WARNING on akpm-mm/mm-everything]
> > 
> > url:    https://github.com/intel-lab-lkp/linux/commits/Anshuman-Khandual/mm-execmem-Make-ARCH_WANTS_EXECMEM_LATE-depend-on-EXECMEM/20241209-111533
> > base:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
> > patch link:    https://lore.kernel.org/r/20241209031251.515903-1-anshuman.khandual%40arm.com
> > patch subject: [PATCH] mm/execmem: Make ARCH_WANTS_EXECMEM_LATE depend on EXECMEM
> > config: arm64-kismet-CONFIG_ARCH_WANTS_EXECMEM_LATE-CONFIG_ARM64-0-0 (https://download.01.org/0day-ci/archive/20241209/202412092048.tTzJ5szH-lkp@intel.com/config)
> > reproduce: (https://download.01.org/0day-ci/archive/20241209/202412092048.tTzJ5szH-lkp@intel.com/reproduce)
> > 
> > If you fix the issue in a separate patch/commit (i.e. not just a new version of
> > the same patch/commit), kindly add following tags
> > | Reported-by: kernel test robot <lkp@intel.com>
> > | Closes: https://lore.kernel.org/oe-kbuild-all/202412092048.tTzJ5szH-lkp@intel.com/
> > 
> > kismet warnings: (new ones prefixed by >>)
> >>> kismet: WARNING: unmet direct dependencies detected for ARCH_WANTS_EXECMEM_LATE when selected by ARM64
> >    WARNING: unmet direct dependencies detected for ARCH_WANTS_EXECMEM_LATE
> >      Depends on [n]: EXECMEM [=n]
> >      Selected by [y]:
> >      - ARM64 [=y]
> 
> Although above mentioned config here has CONFIG_ARCH_WANTS_EXECMEM_LATE=y
> and CONFIG_EXECMEM=n (actually absent), could that really happen though ?
> 
> Tried making CONFIG_EXECMEM=n (rather deselecting) but that did now allow
> setting CONFIG_EXECMEM=n, it always remained set. Reverting this patch i.e
> the current behaviour is also the same (CONFIG_EXECMEM always remains set).
> 
> select ARCH_WANTS_EXECMEM_LATE if EXECMEM
> 
> Above statement seems to be selecting EXECMEM as well but the intent seems
> to be a dependency check instead! OR arch selection for a config brings in
> all its dependencies as well.
> 
> If the selection is always, should this change be like the following ?
> 
> config ARCH_WANTS_EXECMEM_LATE
>  	bool
> 	selects EXECMEM

This is wrong. What ARCH_WANTS_EXECMEM_LATE means is that, _if_ EXECMEM
is enabled, the arch code require its late initialisation. Currently for
arm64 EXECMEM is selected by KPROBES, BPF_JIT and MODULES. So if you
don't have any of these on, you don't need EXECMEM either, no point in
selecting it above just because arm64 wants a specific behaviour (late
initialisation) for EXECMEM.

If you do want a patch for this, I think for arm64 we simply need to
select ARCH_WANTS_EXECMEM_LATE unconditionally. Not much use in having
any dependencies really, it just adds to the clutter. And don't change
the core Kconfig either.

-- 
Catalin