Re: [PATCH v4 02/12] mm/kasan: move kasan= code to common place

[Baoquan He <bhe@redhat.com>]

On 12/04/25 at 05:39pm, Andrey Konovalov wrote:
> On Fri, Nov 28, 2025 at 4:33 AM Baoquan He <bhe@redhat.com> wrote:
> >
> > This allows generic and sw_tags to be set in kernel cmdline too.
> >
> > When at it, rename 'kasan_arg' to 'kasan_arg_disabled' as a bool
> > variable. And expose 'kasan_flag_enabled' to kasan common place
> > too.
> 
> This asks to be two separate patches.

Makes sense to me, thanks..

> 
> >
> > This is prepared for later adding kernel parameter kasan=on|off for
> > all three kasan modes.
> >
> > Signed-off-by: Baoquan He <bhe@redhat.com>
> > ---
> >  include/linux/kasan-enabled.h |  4 +++-
> >  mm/kasan/common.c             | 20 ++++++++++++++++++--
> >  mm/kasan/hw_tags.c            | 28 ++--------------------------
> >  3 files changed, 23 insertions(+), 29 deletions(-)
> >
> > diff --git a/include/linux/kasan-enabled.h b/include/linux/kasan-enabled.h
> > index 9eca967d8526..b05ec6329fbe 100644
> > --- a/include/linux/kasan-enabled.h
> > +++ b/include/linux/kasan-enabled.h
> > @@ -4,13 +4,15 @@
> >
> >  #include <linux/static_key.h>
> >
> > -#if defined(CONFIG_ARCH_DEFER_KASAN) || defined(CONFIG_KASAN_HW_TAGS)
> 
> These changes of moving/removing CONFIG_ARCH_DEFER_KASAN also seem to
> belong to a separate patch (or should be combined with patch 12?); the
> commit message does not even mention them.

Yes, combining tit with patch 12 sounds great. I will move patch 12 to
earlier oder.

> 
> > +extern bool kasan_arg_disabled;
> > +
> >  /*
> >   * Global runtime flag for KASAN modes that need runtime control.
> >   * Used by ARCH_DEFER_KASAN architectures and HW_TAGS mode.
> >   */
> >  DECLARE_STATIC_KEY_FALSE(kasan_flag_enabled);
> 
> So kasan_flag_enabled is now always exposed here...
> 
> >
> > +#if defined(CONFIG_ARCH_DEFER_KASAN) || defined(CONFIG_KASAN_HW_TAGS)
> 
> but the functions that use it are not. Why?

Good question. I didn't consider this reasonably. At the beginning, I
thought it could cause problem if people has specified 'kasan=off'
before patch 12 when bisecting. That's why put kasan_arg_disabled and
kasan_flag_enabled declaration outside of any ifdeffery scope. Now after
reconsiderring, putting patch 12 earlier can solve the problem.

Thanks for careful reivewing, all suggestions are good and taken.

> 
> 
> >  /*
> >   * Runtime control for shadow memory initialization or HW_TAGS mode.
> >   * Uses static key for architectures that need deferred KASAN or HW_TAGS.
> > diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> > index 1d27f1bd260b..ac14956986ee 100644
> > --- a/mm/kasan/common.c
> > +++ b/mm/kasan/common.c
> > @@ -32,14 +32,30 @@
> >  #include "kasan.h"
> >  #include "../slab.h"
> >
> > -#if defined(CONFIG_ARCH_DEFER_KASAN) || defined(CONFIG_KASAN_HW_TAGS)
> >  /*
> >   * Definition of the unified static key declared in kasan-enabled.h.
> >   * This provides consistent runtime enable/disable across KASAN modes.
> >   */
> >  DEFINE_STATIC_KEY_FALSE(kasan_flag_enabled);
> >  EXPORT_SYMBOL_GPL(kasan_flag_enabled);
> > -#endif
> > +
> > +bool kasan_arg_disabled __ro_after_init;
> > +/* kasan=off/on */
> > +static int __init early_kasan_flag(char *arg)
> > +{
> > +       if (!arg)
> > +               return -EINVAL;
> > +
> > +       if (!strcmp(arg, "off"))
> > +               kasan_arg_disabled = true;
> > +       else if (!strcmp(arg, "on"))
> > +               kasan_arg_disabled = false;
> > +       else
> > +               return -EINVAL;
> > +
> > +       return 0;
> > +}
> > +early_param("kasan", early_kasan_flag);
> >
> >  struct slab *kasan_addr_to_slab(const void *addr)
> >  {
> > diff --git a/mm/kasan/hw_tags.c b/mm/kasan/hw_tags.c
> > index 1c373cc4b3fa..709c91abc1b1 100644
> > --- a/mm/kasan/hw_tags.c
> > +++ b/mm/kasan/hw_tags.c
> > @@ -22,12 +22,6 @@
> >
> >  #include "kasan.h"
> >
> > -enum kasan_arg {
> > -       KASAN_ARG_DEFAULT,
> > -       KASAN_ARG_OFF,
> > -       KASAN_ARG_ON,
> > -};
> > -
> >  enum kasan_arg_mode {
> >         KASAN_ARG_MODE_DEFAULT,
> >         KASAN_ARG_MODE_SYNC,
> > @@ -41,7 +35,6 @@ enum kasan_arg_vmalloc {
> >         KASAN_ARG_VMALLOC_ON,
> >  };
> >
> > -static enum kasan_arg kasan_arg __ro_after_init;
> >  static enum kasan_arg_mode kasan_arg_mode __ro_after_init;
> >  static enum kasan_arg_vmalloc kasan_arg_vmalloc __initdata;
> >
> > @@ -81,23 +74,6 @@ unsigned int kasan_page_alloc_sample_order = PAGE_ALLOC_SAMPLE_ORDER_DEFAULT;
> >
> >  DEFINE_PER_CPU(long, kasan_page_alloc_skip);
> >
> > -/* kasan=off/on */
> > -static int __init early_kasan_flag(char *arg)
> > -{
> > -       if (!arg)
> > -               return -EINVAL;
> > -
> > -       if (!strcmp(arg, "off"))
> > -               kasan_arg = KASAN_ARG_OFF;
> > -       else if (!strcmp(arg, "on"))
> > -               kasan_arg = KASAN_ARG_ON;
> > -       else
> > -               return -EINVAL;
> > -
> > -       return 0;
> > -}
> > -early_param("kasan", early_kasan_flag);
> > -
> >  /* kasan.mode=sync/async/asymm */
> >  static int __init early_kasan_mode(char *arg)
> >  {
> > @@ -222,7 +198,7 @@ void kasan_init_hw_tags_cpu(void)
> >          * When this function is called, kasan_flag_enabled is not yet
> >          * set by kasan_init_hw_tags(). Thus, check kasan_arg instead.
> >          */
> > -       if (kasan_arg == KASAN_ARG_OFF)
> > +       if (kasan_arg_disabled)
> >                 return;
> >
> >         /*
> > @@ -240,7 +216,7 @@ void __init kasan_init_hw_tags(void)
> >                 return;
> >
> >         /* If KASAN is disabled via command line, don't initialize it. */
> > -       if (kasan_arg == KASAN_ARG_OFF)
> > +       if (kasan_arg_disabled)
> >                 return;
> >
> >         switch (kasan_arg_mode) {
> > --
> > 2.41.0
> >
>