Re: [PATCH 3/4] mm: Support only one page_type per page

[Matthew Wilcox <willy@infradead.org>]

On Wed, Aug 28, 2024 at 11:35:28AM +0800, Kefeng Wang wrote:
> There are some UBSAN warning about  __folio_set_##fname/__SetPage##uname,
> 
> UBSAN: shift-out-of-bounds in ../include/linux/page-flags.h:998:1
> left shift of 240 by 24 places cannot be represented in type 'int'

I can't reproduce this.  I know Andrew merged this patch in, but I
tried backing it out and enabling UBSAN and it doesn't show up for me.
Relevant part of .config:

CONFIG_ARCH_HAS_UBSAN=y
CONFIG_UBSAN=y
CONFIG_UBSAN_TRAP=y
CONFIG_CC_HAS_UBSAN_BOUNDS_STRICT=y
CONFIG_UBSAN_BOUNDS=y
CONFIG_UBSAN_BOUNDS_STRICT=y
CONFIG_UBSAN_SHIFT=y
# CONFIG_UBSAN_DIV_ZERO is not set
CONFIG_UBSAN_BOOL=y
CONFIG_UBSAN_ENUM=y
# CONFIG_TEST_UBSAN is not set

(I tried CONFIG_UBSAN_TRAP both on and off)

> Changing significant bit to unsigned to fix it.
> 
> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> index 28d2337525d1..2175ebceb41c 100644
> --- a/include/linux/page-flags.h
> +++ b/include/linux/page-flags.h
> @@ -966,7 +966,7 @@ static __always_inline void __folio_set_##fname(struct
> folio *folio)        \
>  {                                                                      \
>         VM_BUG_ON_FOLIO(data_race(folio->page.page_type) != UINT_MAX,   \
>                         folio);                                         \
> -       folio->page.page_type = PGTY_##lname << 24;                     \
> +       folio->page.page_type = (unsigned int)PGTY_##lname << 24;       \
>  }                                                                      \
>  static __always_inline void __folio_clear_##fname(struct folio *folio) \
>  {                                                                      \
> @@ -983,7 +983,7 @@ static __always_inline int Page##uname(const struct page
> *page)             \
>  static __always_inline void __SetPage##uname(struct page *page)         \
>  {                                                                      \
>         VM_BUG_ON_PAGE(data_race(page->page_type) != UINT_MAX, page);   \
> -       page->page_type = PGTY_##lname << 24;                           \
> +       page->page_type = (unsigned int)PGTY_##lname << 24;             \
>  }                                                                      \
> 
> 
>