[PATCH mm v3 28/38] kasan, page_alloc: allow skipping memory init for HW_TAGS

[Andrey Konovalov]

On Fri, Dec 17, 2021 at 2:50 AM Kuan-Ying Lee
<Kuan-Ying.Lee at mediatek.com> wrote:
>
> On Tue, 2021-12-14 at 05:54 +0800, andrey.konovalov at linux.dev wrote:
> > From: Andrey Konovalov <andreyknvl at google.com>
> >
> > Add a new GFP flag __GFP_SKIP_ZERO that allows to skip memory
> > initialization. The flag is only effective with HW_TAGS KASAN.
> >
> > This flag will be used by vmalloc code for page_alloc allocations
> > backing vmalloc() mappings in a following patch. The reason to skip
> > memory initialization for these pages in page_alloc is because
> > vmalloc
> > code will be initializing them instead.
> >
> > With the current implementation, when __GFP_SKIP_ZERO is provided,
> > __GFP_ZEROTAGS is ignored. This doesn't matter, as these two flags
> > are
> > never provided at the same time. However, if this is changed in the
> > future, this particular implementation detail can be changed as well.
> >
> > Signed-off-by: Andrey Konovalov <andreyknvl at google.com>
> >
> > ---
> >
> > Changes v2->v3:
> > - Update patch description.
> >
> > Changes v1->v2:
> > - Add this patch.
> > ---
> >  include/linux/gfp.h | 16 +++++++++++-----
> >  mm/page_alloc.c     | 13 ++++++++++++-
> >  2 files changed, 23 insertions(+), 6 deletions(-)
> >
> > diff --git a/include/linux/gfp.h b/include/linux/gfp.h
> > index 6781f84345d1..b8b1a7198186 100644
> > --- a/include/linux/gfp.h
> > +++ b/include/linux/gfp.h
> > @@ -54,10 +54,11 @@ struct vm_area_struct;
> >  #define ___GFP_THISNODE              0x200000u
> >  #define ___GFP_ACCOUNT               0x400000u
> >  #define ___GFP_ZEROTAGS              0x800000u
> > -#define ___GFP_SKIP_KASAN_UNPOISON   0x1000000u
> > -#define ___GFP_SKIP_KASAN_POISON     0x2000000u
> > +#define ___GFP_SKIP_ZERO     0x1000000u
> > +#define ___GFP_SKIP_KASAN_UNPOISON   0x2000000u
> > +#define ___GFP_SKIP_KASAN_POISON     0x4000000u
> >  #ifdef CONFIG_LOCKDEP
> > -#define ___GFP_NOLOCKDEP     0x4000000u
> > +#define ___GFP_NOLOCKDEP     0x8000000u
> >  #else
> >  #define ___GFP_NOLOCKDEP     0
> >  #endif
> > @@ -230,7 +231,11 @@ struct vm_area_struct;
> >   * %__GFP_ZERO returns a zeroed page on success.
> >   *
> >   * %__GFP_ZEROTAGS zeroes memory tags at allocation time if the
> > memory itself
> > - * is being zeroed (either via __GFP_ZERO or via init_on_alloc).
> > + * is being zeroed (either via __GFP_ZERO or via init_on_alloc,
> > provided that
> > + * __GFP_SKIP_ZERO is not set).
> > + *
> > + * %__GFP_SKIP_ZERO makes page_alloc skip zeroing memory.
> > + * Only effective when HW_TAGS KASAN is enabled.
> >   *
> >   * %__GFP_SKIP_KASAN_UNPOISON makes KASAN skip unpoisoning on page
> > allocation.
> >   * Only effective in HW_TAGS mode.
> > @@ -242,6 +247,7 @@ struct vm_area_struct;
> >  #define __GFP_COMP   ((__force gfp_t)___GFP_COMP)
> >  #define __GFP_ZERO   ((__force gfp_t)___GFP_ZERO)
> >  #define __GFP_ZEROTAGS       ((__force gfp_t)___GFP_ZEROTAGS)
> > +#define __GFP_SKIP_ZERO ((__force gfp_t)___GFP_SKIP_ZERO)
> >  #define __GFP_SKIP_KASAN_UNPOISON ((__force
> > gfp_t)___GFP_SKIP_KASAN_UNPOISON)
> >  #define __GFP_SKIP_KASAN_POISON   ((__force
> > gfp_t)___GFP_SKIP_KASAN_POISON)
> >
> > @@ -249,7 +255,7 @@ struct vm_area_struct;
> >  #define __GFP_NOLOCKDEP ((__force gfp_t)___GFP_NOLOCKDEP)
> >
> >  /* Room for N __GFP_FOO bits */
> > -#define __GFP_BITS_SHIFT (26 + IS_ENABLED(CONFIG_LOCKDEP))
> > +#define __GFP_BITS_SHIFT (27 + IS_ENABLED(CONFIG_LOCKDEP))
> >  #define __GFP_BITS_MASK ((__force gfp_t)((1 << __GFP_BITS_SHIFT) -
> > 1))
> >
> >  /**
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index f1d5b80591c4..af7516a2d5ea 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -2409,10 +2409,21 @@ static inline bool
> > should_skip_kasan_unpoison(gfp_t flags, bool init_tags)
> >       return init_tags || (flags & __GFP_SKIP_KASAN_UNPOISON);
> >  }
> >
> > +static inline bool should_skip_init(gfp_t flags)
> > +{
> > +     /* Don't skip if a software KASAN mode is enabled. */
> > +     if (!IS_ENABLED(CONFIG_KASAN_HW_TAGS))
> > +             return false;
> > +
>
> Hi Andrey,
>
> Should we use kasan_hw_tags_enabled() in should_skip_init() function
> instead of checking the config?
>
> I think we should handle the condition which is CONFIG_KASAN_HW_TAGS=y
> and command line="kasan=off".

Hi Kuan-Ying,

You are right! Will fix in v4.

Thanks!