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Message-ID: <CACzwLxi5AKT_81ej4AZ1ztsncBDY4jDJCyWboF0X9-kiH_=NMA@mail.gmail.com>
Date: Sun, 10 Aug 2025 12:32:08 +0500
From: Sabyrzhan Tasbolatov <snovitoll@...il.com>
To: Christophe Leroy <christophe.leroy@...roup.eu>
Cc: ryabinin.a.a@...il.com, bhe@...hat.com, hca@...ux.ibm.com,
andreyknvl@...il.com, akpm@...ux-foundation.org, zhangqing@...ngson.cn,
chenhuacai@...ngson.cn, glider@...gle.com, dvyukov@...gle.com, alex@...ti.fr,
agordeev@...ux.ibm.com, vincenzo.frascino@....com, elver@...gle.com,
kasan-dev@...glegroups.com, linux-arm-kernel@...ts.infradead.org,
linux-kernel@...r.kernel.org, loongarch@...ts.linux.dev,
linuxppc-dev@...ts.ozlabs.org, linux-riscv@...ts.infradead.org,
linux-s390@...r.kernel.org, linux-um@...ts.infradead.org, linux-mm@...ck.org,
davidgow@...gle.com
Subject: Re: [PATCH v5 1/2] kasan: introduce ARCH_DEFER_KASAN and unify static
key across modes
On Sun, Aug 10, 2025 at 12:20 PM Sabyrzhan Tasbolatov
<snovitoll@...il.com> wrote:
>
> On Fri, Aug 8, 2025 at 10:03 PM Christophe Leroy
> <christophe.leroy@...roup.eu> wrote:
> >
> >
> >
> > Le 08/08/2025 à 17:33, Sabyrzhan Tasbolatov a écrit :
> > > On Fri, Aug 8, 2025 at 10:03 AM Christophe Leroy
> > > <christophe.leroy@...roup.eu> wrote:
> > >>
> > >>
> > >>
> > >> Le 07/08/2025 à 21:40, Sabyrzhan Tasbolatov a écrit :
> > >>> Introduce CONFIG_ARCH_DEFER_KASAN to identify architectures [1] that need
> > >>> to defer KASAN initialization until shadow memory is properly set up,
> > >>> and unify the static key infrastructure across all KASAN modes.
> > >>
> > >> That probably desserves more details, maybe copy in informations from
> > >> the top of cover letter.
> > >>
> > >> I think there should also be some exeplanations about
> > >> kasan_arch_is_ready() becoming kasan_enabled(), and also why
> > >> kasan_arch_is_ready() completely disappear from mm/kasan/common.c
> > >> without being replaced by kasan_enabled().
> > >>
> > >>>
> > >>> [1] PowerPC, UML, LoongArch selects ARCH_DEFER_KASAN.
> > >>>
> > >>> Closes: https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fbugzilla.kernel.org%2Fshow_bug.cgi%3Fid%3D217049&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7Cfe4f5a759ad6452b047408ddd691024a%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C638902640503259176%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=UM4uvQihJdeWwcC6DIiJXbn4wGsrijjRcHc55uCMErI%3D&reserved=0
> > >>> Signed-off-by: Sabyrzhan Tasbolatov <snovitoll@...il.com>
> > >>> ---
> > >>> Changes in v5:
> > >>> - Unified patches where arch (powerpc, UML, loongarch) selects
> > >>> ARCH_DEFER_KASAN in the first patch not to break
> > >>> bisectability
> > >>> - Removed kasan_arch_is_ready completely as there is no user
> > >>> - Removed __wrappers in v4, left only those where it's necessary
> > >>> due to different implementations
> > >>>
> > >>> Changes in v4:
> > >>> - Fixed HW_TAGS static key functionality (was broken in v3)
> > >>> - Merged configuration and implementation for atomicity
> > >>> ---
> > >>> arch/loongarch/Kconfig | 1 +
> > >>> arch/loongarch/include/asm/kasan.h | 7 ------
> > >>> arch/loongarch/mm/kasan_init.c | 8 +++----
> > >>> arch/powerpc/Kconfig | 1 +
> > >>> arch/powerpc/include/asm/kasan.h | 12 ----------
> > >>> arch/powerpc/mm/kasan/init_32.c | 2 +-
> > >>> arch/powerpc/mm/kasan/init_book3e_64.c | 2 +-
> > >>> arch/powerpc/mm/kasan/init_book3s_64.c | 6 +----
> > >>> arch/um/Kconfig | 1 +
> > >>> arch/um/include/asm/kasan.h | 5 ++--
> > >>> arch/um/kernel/mem.c | 10 ++++++--
> > >>> include/linux/kasan-enabled.h | 32 ++++++++++++++++++--------
> > >>> include/linux/kasan.h | 6 +++++
> > >>> lib/Kconfig.kasan | 8 +++++++
> > >>> mm/kasan/common.c | 17 ++++++++++----
> > >>> mm/kasan/generic.c | 19 +++++++++++----
> > >>> mm/kasan/hw_tags.c | 9 +-------
> > >>> mm/kasan/kasan.h | 8 ++++++-
> > >>> mm/kasan/shadow.c | 12 +++++-----
> > >>> mm/kasan/sw_tags.c | 1 +
> > >>> mm/kasan/tags.c | 2 +-
> > >>> 21 files changed, 100 insertions(+), 69 deletions(-)
> > >>>
> > >>> diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
> > >>> index f0abc38c40a..cd64b2bc12d 100644
> > >>> --- a/arch/loongarch/Kconfig
> > >>> +++ b/arch/loongarch/Kconfig
> > >>> @@ -9,6 +9,7 @@ config LOONGARCH
> > >>> select ACPI_PPTT if ACPI
> > >>> select ACPI_SYSTEM_POWER_STATES_SUPPORT if ACPI
> > >>> select ARCH_BINFMT_ELF_STATE
> > >>> + select ARCH_DEFER_KASAN if KASAN
> > >>
> > >> Instead of adding 'if KASAN' in all users, you could do in two steps:
> > >>
> > >> Add a symbol ARCH_NEEDS_DEFER_KASAN.
> > >>
> > >> +config ARCH_NEEDS_DEFER_KASAN
> > >> + bool
> > >>
> > >> And then:
> > >>
> > >> +config ARCH_DEFER_KASAN
> > >> + def_bool
> > >> + depends on KASAN
> > >> + depends on ARCH_DEFER_KASAN
> > >> + help
> > >> + Architectures should select this if they need to defer KASAN
> > >> + initialization until shadow memory is properly set up. This
> > >> + enables runtime control via static keys. Otherwise, KASAN uses
> > >> + compile-time constants for better performance.
> > >>
> > >
> > > Actually, I don't see the benefits from this option. Sorry, have just
> > > revisited this again.
> > > With the new symbol, arch (PowerPC, UML, LoongArch) still needs select
> > > 2 options:
> > >
> > > select ARCH_NEEDS_DEFER_KASAN
> > > select ARCH_DEFER_KASAN
> >
> > Sorry, my mistake, ARCH_DEFER_KASAN has to be 'def_bool y'. Missing the
> > 'y'. That way it is automatically set to 'y' as long as KASAN and
> > ARCH_NEEDS_DEFER_KASAN are selected. Should be:
> >
> > config ARCH_DEFER_KASAN
> > def_bool y
> > depends on KASAN
> > depends on ARCH_NEEDS_DEFER_KASAN
> >
> >
> > >
> > > and the oneline with `if` condition is cleaner.
> > > select ARCH_DEFER_KASAN if KASAN
>
> Hello,
>
> Have just had a chance to test this.
>
> lib/Kconfig.kasan:
> config ARCH_NEEDS_DEFER_KASAN
> bool
>
> config ARCH_DEFER_KASAN
> def_bool y
> depends on KASAN
> depends on ARCH_NEEDS_DEFER_KASAN
Setting Kconfig.kasan without KASAN works fine for 3 arch that selects
ARCH_DEFER_KASAN:
config ARCH_DEFER_KASAN
def_bool y
depends on ARCH_NEEDS_DEFER_KASAN
Going to send v6 soon.
P.S.: Fixed email of David Gow.
>
> It works for UML defconfig where arch/um/Kconfig is:
>
> config UML
> bool
> default y
> select ARCH_NEEDS_DEFER_KASAN
> select ARCH_DEFER_KASAN if STATIC_LINK
>
> But it prints warnings for PowerPC, LoongArch:
>
> config LOONGARCH
> bool
> ...
> select ARCH_NEEDS_DEFER_KASAN
> select ARCH_DEFER_KASAN
>
> $ make defconfig ARCH=loongarch
> *** Default configuration is based on 'loongson3_defconfig'
>
> WARNING: unmet direct dependencies detected for ARCH_DEFER_KASAN
> Depends on [n]: KASAN [=n] && ARCH_NEEDS_DEFER_KASAN [=y]
> Selected by [y]:
> - LOONGARCH [=y]
>
>
> config PPC
> bool
> default y
> select ARCH_DEFER_KASAN if PPC_RADIX_MMU
> select ARCH_NEEDS_DEFER_KASAN
>
> $ make ppc64_defconfig
>
> WARNING: unmet direct dependencies detected for ARCH_DEFER_KASAN
> Depends on [n]: KASAN [=n] && ARCH_NEEDS_DEFER_KASAN [=y]
> Selected by [y]:
> - PPC [=y] && PPC_RADIX_MMU [=y]
>
>
> > >
> >
> > I don't think so because it requires all architectures to add 'if KASAN'
> > which is not convenient.
> >
> > Christophe
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