Re: [PATCH v11 3/9] powerpc: Always define MODULES_{VADDR,END}

From: Jordan Niethe <jniethe5@gmail.com>
To: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: ajd@linux.ibm.com, Nicholas Piggin <npiggin@gmail.com>,
	cmr@codefail.de, "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
	naveen.n.rao@linux.ibm.com,
	linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
	Daniel Axtens <dja@axtens.net>
Subject: Re: [PATCH v11 3/9] powerpc: Always define MODULES_{VADDR,END}
Date: Mon, 3 May 2021 16:16:48 +1000	[thread overview]
Message-ID: <CACzsE9r-FBSo9F79cKj9c3gE7g821AhoLsRPWwd=7eFm+gMpTw@mail.gmail.com> (raw)
In-Reply-To: <6fa81d25-4313-5f15-23d9-06b314bb7d02@csgroup.eu>

On Mon, May 3, 2021 at 3:57 PM Christophe Leroy
<christophe.leroy@csgroup.eu> wrote:
>
>
>
> Le 03/05/2021 à 07:39, Jordan Niethe a écrit :
> > On Thu, Apr 29, 2021 at 3:04 PM Christophe Leroy
> > <christophe.leroy@csgroup.eu> wrote:
> >>
> >>
> >>
> >> Le 29/04/2021 à 05:15, Jordan Niethe a écrit :
> >>> If MODULES_{VADDR,END} are not defined set them to VMALLOC_START and
> >>> VMALLOC_END respectively. This reduces the need for special cases. For
> >>> example, powerpc's module_alloc() was previously predicated on
> >>> MODULES_VADDR being defined but now is unconditionally defined.
> >>>
> >>> This will be useful reducing conditional code in other places that need
> >>> to allocate from the module region (i.e., kprobes).
> >>>
> >>> Signed-off-by: Jordan Niethe <jniethe5@gmail.com>
> >>> ---
> >>> v10: New to series
> >>> v11: - Consider more places MODULES_VADDR was being used
> >>> ---
> >>>    arch/powerpc/include/asm/pgtable.h    | 11 +++++++++++
> >>>    arch/powerpc/kernel/module.c          |  5 +----
> >>>    arch/powerpc/mm/kasan/kasan_init_32.c | 10 +++++-----
> >>>    arch/powerpc/mm/ptdump/ptdump.c       |  4 ++--
> >>>    4 files changed, 19 insertions(+), 11 deletions(-)
> >>>
> >>> diff --git a/arch/powerpc/include/asm/pgtable.h b/arch/powerpc/include/asm/pgtable.h
> >>> index c6a676714f04..882fda779648 100644
> >>> --- a/arch/powerpc/include/asm/pgtable.h
> >>> +++ b/arch/powerpc/include/asm/pgtable.h
> >>> @@ -39,6 +39,17 @@ struct mm_struct;
> >>>    #define __S110      PAGE_SHARED_X
> >>>    #define __S111      PAGE_SHARED_X
> >>>
> >>> +#ifndef MODULES_VADDR
> >>> +#define MODULES_VADDR VMALLOC_START
> >>> +#define MODULES_END VMALLOC_END
> >>> +#endif
> >>> +
> >>> +#if defined(CONFIG_PPC_BOOK3S_32) && defined(CONFIG_STRICT_KERNEL_RWX)
> >>
> >> No no.
> >>
> >> TASK_SIZE > MODULES_VADDR is ALWAYS wrong, for any target, in any configuration.
> >>
> >> Why is it a problem to leave the test as a BUILD_BUG_ON() in module_alloc() ?
> > On ppc64s, MODULES_VADDR is __vmalloc_start (a variable)  and
> > TASK_SIZE depends on current.
> > Also for nohash like 44x, MODULES_VADDR is defined based on high_memory.
> > If I put it back in module_alloc() and wrap it with #ifdef
> > CONFIG_PPC_BOOK3S_32 will that be fine?
>
> Thinking about it once more, I think the best approach is the one taken by Nick in
> https://patchwork.ozlabs.org/project/linuxppc-dev/patch/20210502110050.324953-1-npiggin@gmail.com/
>
> Use MODULES_VADDR/MODULES_END when it exists, use VMALLOC_START/VMALLOC_END otherwise.
>
> I know I suggested to always define MODULES_VADDR, but maybe that's not the best solution at the end.
Sure, let's do it like that.
>
> For kprobes, is there a way to re-use functions from modules.c in alloc_insn_page() ?
Probably we can use module_alloc() then the set_memory_ functions to
get the permissions right.
Something like we had in v9:
https://lore.kernel.org/linuxppc-dev/20210316031741.1004850-3-jniethe5@gmail.com/
>
> Christophe