On Fri, 2021-12-31 at 03:14 +0800, andrey.konovalov@xxxxxxxxx wrote:
> From: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
>
> 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@xxxxxxxxxx>
>
> ---
>
> Changes v4->v5:
> - Cosmetic changes to __def_gfpflag_names_kasan and __GFP_BITS_SHIFT.
>
> Changes v3->v4:
> - Only define __GFP_SKIP_ZERO when CONFIG_KASAN_HW_TAGS is enabled.
> - Add __GFP_SKIP_ZERO to include/trace/events/mmflags.h.
> - Use proper kasan_hw_tags_enabled() check instead of
> IS_ENABLED(CONFIG_KASAN_HW_TAGS). Also add explicit checks for
> software modes.
>
> Changes v2->v3:
> - Update patch description.
>
> Changes v1->v2:
> - Add this patch.
> ---
> include/linux/gfp.h | 18 +++++++++++-------
> include/trace/events/mmflags.h | 1 +
> mm/page_alloc.c | 18 +++++++++++++++++-
> 3 files changed, 29 insertions(+), 8 deletions(-)
>
> diff --git a/include/linux/gfp.h b/include/linux/gfp.h
> index 487126f089e1..6eef3e447540 100644
> --- a/include/linux/gfp.h
> +++ b/include/linux/gfp.h
> @@ -55,14 +55,16 @@ struct vm_area_struct;
> #define ___GFP_ACCOUNT 0x400000u
> #define ___GFP_ZEROTAGS 0x800000u
> #ifdef CONFIG_KASAN_HW_TAGS
> -#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
> #else
> +#define ___GFP_SKIP_ZERO 0
> #define ___GFP_SKIP_KASAN_UNPOISON 0
> #define ___GFP_SKIP_KASAN_POISON 0
> #endif
> #ifdef CONFIG_LOCKDEP
> -#define ___GFP_NOLOCKDEP 0x4000000u
> +#define ___GFP_NOLOCKDEP 0x8000000u
> #else
> #define ___GFP_NOLOCKDEP 0
> #endif
> @@ -235,9 +237,10 @@ 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).
> This flag is
> - * intended for optimization: setting memory tags at the same time
> as zeroing
> - * memory has minimal additional performace impact.
> + * is being zeroed (either via __GFP_ZERO or via init_on_alloc,
> provided that
> + * __GFP_SKIP_ZERO is not set). This flag is intended for
> optimization: setting
> + * memory tags at the same time as zeroing memory has minimal
> additional
> + * performace impact.
> *
> * %__GFP_SKIP_KASAN_UNPOISON makes KASAN skip unpoisoning on page
> allocation.
> * Only effective in HW_TAGS mode.
> @@ -249,6 +252,7 @@ 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)
>
> @@ -257,7 +261,7 @@ struct vm_area_struct;
>
> /* Room for N __GFP_FOO bits */
> #define __GFP_BITS_SHIFT (24 +
> \
> - 2 * IS_ENABLED(CONFIG_KASAN_HW_TAGS) + \
> + 3 * IS_ENABLED(CONFIG_KASAN_HW_TAGS) + \
> IS_ENABLED(CONFIG_LOCKDEP))
> #define __GFP_BITS_MASK ((__force gfp_t)((1 << __GFP_BITS_SHIFT) -
> 1))
>
> diff --git a/include/trace/events/mmflags.h
> b/include/trace/events/mmflags.h
> index 5ffc7bdce91f..0698c5d0f194 100644
> --- a/include/trace/events/mmflags.h
> +++ b/include/trace/events/mmflags.h
> @@ -52,6 +52,7 @@
>
> #ifdef CONFIG_KASAN_HW_TAGS
> #define __def_gfpflag_names_kasan ,
> \
> + {(unsigned long)__GFP_SKIP_ZERO, "__GFP_SKIP_ZERO"},
> \
> {(unsigned
> long)__GFP_SKIP_KASAN_POISON, "__GFP_SKIP_KASAN_POISON"}, \
> {(unsigned long)__GFP_SKIP_KASAN_UNPOISON,
> "__GFP_SKIP_KASAN_UNPOISON"}
> #else
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 102f0cd8815e..30da0e1f94f8 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2415,10 +2415,26 @@ 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_GENERIC) ||
> + IS_ENABLED(CONFIG_KASAN_SW_TAGS))
> + return false;
Forget to drop the above check?
I saw v4 mentioned that this check can be dropped. [1]
Do I miss something?
[1] https://lkml.org/lkml/2021/12/30/450
> +
> + /* Don't skip, if hardware tag-based KASAN is not enabled. */
> + if (!kasan_hw_tags_enabled())
> + return false;
> +
> + /* For hardware tag-based KASAN, skip if requested. */
> + return (flags & __GFP_SKIP_ZERO);
> +}
> +
> inline void post_alloc_hook(struct page *page, unsigned int order,
> gfp_t gfp_flags)
> {
> - bool init = !want_init_on_free() &&
> want_init_on_alloc(gfp_flags);
> + bool init = !want_init_on_free() &&
> want_init_on_alloc(gfp_flags) &&
> + !should_skip_init(gfp_flags);
> bool init_tags = init && (gfp_flags & __GFP_ZEROTAGS);
>
> set_page_private(page, 0);
> --
> 2.25.1
>
>
