linux-kernel - Re: [PATCH v15 03/11] riscv/Kconfig: make direct map manipulation options depend on MMU

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Message-ID: <mhng-0c84abc1-8ac8-4142-be1c-a269d8b345f8@palmerdabbelt-glaptop>
Date:   Tue, 26 Jan 2021 21:46:18 -0800 (PST)
From:   Palmer Dabbelt <palmer@...belt.com>
To:     rppt@...nel.org
CC:     akpm@...ux-foundation.org, viro@...iv.linux.org.uk,
        luto@...nel.org, Arnd Bergmann <arnd@...db.de>, bp@...en8.de,
        catalin.marinas@....com, cl@...ux.com, dan.j.williams@...el.com,
        dave.hansen@...ux.intel.com, david@...hat.com,
        elena.reshetova@...el.com, hpa@...or.com, mingo@...hat.com,
        jejb@...ux.ibm.com, kirill@...temov.name, willy@...radead.org,
        mark.rutland@....com, rppt@...ux.ibm.com, mtk.manpages@...il.com,
        Paul Walmsley <paul.walmsley@...ive.com>, peterz@...radead.org,
        rick.p.edgecombe@...el.com, guro@...com, shakeelb@...gle.com,
        shuah@...nel.org, tglx@...utronix.de, tycho@...ho.ws,
        will@...nel.org, linux-api@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-nvdimm@...ts.01.org, linux-riscv@...ts.infradead.org,
        x86@...nel.org, lkp@...el.com
Subject:     Re: [PATCH v15 03/11] riscv/Kconfig: make direct map manipulation options depend on MMU

On Sat, 23 Jan 2021 03:00:41 PST (-0800), rppt@...nel.org wrote:
> On Fri, Jan 22, 2021 at 08:12:30PM -0800, Palmer Dabbelt wrote:
>> On Wed, 20 Jan 2021 10:06:04 PST (-0800), rppt@...nel.org wrote:
>> > From: Mike Rapoport <rppt@...ux.ibm.com>
>> >
>> > ARCH_HAS_SET_DIRECT_MAP and ARCH_HAS_SET_MEMORY configuration options have
>> > no meaning when CONFIG_MMU is disabled and there is no point to enable them
>> > for the nommu case.
>> >
>> > Add an explicit dependency on MMU for these options.
>> >
>> > Signed-off-by: Mike Rapoport <rppt@...ux.ibm.com>
>> > Reported-by: kernel test robot <lkp@...el.com>
>> > ---
>> >  arch/riscv/Kconfig | 4 ++--
>> >  1 file changed, 2 insertions(+), 2 deletions(-)
>> >
>> > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
>> > index d82303dcc6b6..d35ce19ab1fa 100644
>> > --- a/arch/riscv/Kconfig
>> > +++ b/arch/riscv/Kconfig
>> > @@ -25,8 +25,8 @@ config RISCV
>> >  	select ARCH_HAS_KCOV
>> >  	select ARCH_HAS_MMIOWB
>> >  	select ARCH_HAS_PTE_SPECIAL
>> > -	select ARCH_HAS_SET_DIRECT_MAP
>> > -	select ARCH_HAS_SET_MEMORY
>> > +	select ARCH_HAS_SET_DIRECT_MAP if MMU
>> > +	select ARCH_HAS_SET_MEMORY if MMU
>> >  	select ARCH_HAS_STRICT_KERNEL_RWX if MMU
>> >  	select ARCH_OPTIONAL_KERNEL_RWX if ARCH_HAS_STRICT_KERNEL_RWX
>> >  	select ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
>>
>> Reviewed-by: Palmer Dabbelt <palmerdabbelt@...gle.com>
>> Acked-by: Palmer Dabbelt <palmerdabbelt@...gle.com>
>>
>> LMK if you want this to go in via the RISC-V tree, otherwise I'm going to
>> assume it's going in along with the rest of these.  FWIW I see these in other
>> architectures without the MMU guard.
>
> Except arm, they all always have MMU=y and arm selects only
> ARCH_HAS_SET_MEMORY and has empty stubs for those when MMU=n.

OK, maybe I just checked ARM, then.  I was just making sure.

> Indeed I might have been over zealous adding ARCH_HAS_SET_MEMORY dependency
> on MMU, as riscv also has these stubs, but I thought that making this
> explicit is a nice thing.

It seems reasonable to me.

Thanks!