Re: [PATCH v4] mm/memory: use pmdp_get_lockless() for the pmd read in do_fault_around()

["David Hildenbrand (Arm)" <david@kernel.org>]

On 11/9/26 15:02, Greg Ungerer wrote:
> Hi Hui,
> 
> On 9/11/26 15:50, Hui Zhu wrote:
>> 2026/11/6 20:08, Greg Ungerer:
>>
>> Hi Greg,
>>
>>> Hi Hui,
>>>
>>> The m5475evb_defconfig is supposed to have MMU enabled:
>>>
>>>       $ ARCH=m68k CROSS_COMPILE=m68k-linux-uclibc- make m5475evb_defconfig
>>>         HOSTCC  scripts/basic/fixdep
>>>         [snip]
>>>         HOSTLD  scripts/kconfig/conf
>>>       #
>>>       # configuration written to .config
>>>       #
>>>       $
>>>       $ grep CONFIG_MMU .config
>>>       CONFIG_MMU=y
>>>       CONFIG_MMU_COLDFIRE=y
>>>       CONFIG_MMU_GATHER_NO_RANGE=y
>>>       CONFIG_MMU_GATHER_MERGE_VMAS=y
>>>       CONFIG_MMU_LAZY_TLB_REFCOUNT=y
>>>
>>> But something ends up disabling it when you compile.
>>> I'll fix this.
>>>
>>>
>>> You should not be able to set MMU=y if configured for the M5208.
>>> It doesn't have an MMU. You want the 5475, 5485 or 54418 to test
>>> valid MMU=y configurations.
>>>
>>> Regards
>>> Greg
>>>
>>>
>>>
>>
>> You are right on both counts, and that mail of mine had three things
>> wrong.
>>
>> 1. "No m52xx/m54xx defconfig enables CONFIG_MMU" - wrong.  I grepped the
>> defconfig fragments for CONFIG_MMU=y, but MMU is 'default y', so an
>> enabled MMU never appears in the fragment.  m5475evb and m54418evb
>> both give CONFIG_MMU=y, as you show.
>>
>> 2. My "m5208evb + CONFIG_MMU=y" test config was not a valid config.
>> M520x is 'depends on !MMU', so forcing MMU on leaves the SoC choice
>> unsatisfiable and olddefconfig silently drops it:
>>
>> before:  # CONFIG_MMU is not set / CONFIG_M520x=y
>> after:   CONFIG_MMU=y / CONFIG_MMU_COLDFIRE=y / CONFIG_M520x gone
>>
>> Please disregard the m5208evb row in my codegen numbers.
>>
>> 3. The "red herring" I flagged was my own doing, not a pre-existing
>> problem.  mm/Makefile has 'mmu-$(CONFIG_MMU) := ... memory.o', so a
>> NOMMU config never builds mm/memory.o at all; I asked for a target
>> that config does not have.  Sorry for the noise on that one.
>>
>> Retested with the configs you named (7.4-rc1 plus the do_fault_around
>> change plus David's cleanup, gcc-m68k-linux-gnu 13.3.0):
>>
>> m5475evb_defconfig   without David's patch: mm/memory.o fails at
>> mcf_pgtable.h:134 with it: full -j24 build ok, vmlinux 4215344
>> bytes, 0 warnings
>>
>> m54418evb_defconfig  without David's patch: same mcf_pgtable.h:134
>> failure
>>
>> So the Tested-by I sent covers amiga, sun3 and m5475evb.  It is
>> build-tested only - I have no m68k hardware here to boot.
> 
> Thanks for retesting. Looks good.
> 
> 
>> On MMU being disabled when you compile: I cannot reproduce that. Here
>> m5475evb_defconfig gives CONFIG_MMU=y, olddefconfig reports no change,
>> two consecutive defconfig runs produce an identical .config, and a full
>> build finishes with CONFIG_MMU=y and CONFIG_M547x=y still set and
>> .config untouched.  Two differences from your setup that might matter:
>> I am on a glibc toolchain rather than uclibc, and building out of tree
>> with O= rather than in tree.
> 
> I can't reproduce either now. I must have done something silly when
> quickly double checking that config. Multiple configures and builds
> and I think it is all doing the right things at configuration and build.
> 
> 
>> One observation, which may well be unrelated.  m5475evb_defconfig never
>> sets CONFIG_M547x - it only ends up with it because the "ColdFire SoC
>> type" choice defaults to M520x, which is unavailable under MMU=y, so
>> kconfig falls back to the first usable member. m54418evb_defconfig sets
>> CONFIG_M5441x=y explicitly.  If that fallback is what breaks on your
>> side, making m5475evb explicit would sidestep it.
> 
> FWIW, running "make savedefconfig" on a fully built m5475evb configuration
> results in an identical defconfig to arch/m68k/configs/m5475evb_defconfig.
> 
> Anyway, I applied both changes and tested on real hardware. All seems to
> work fine. So for ColdFire:
> 
>     Tested-by: Greg Ungerer <gerg@linux-m68k.org>

Thanks!

-- 
Cheers,

David