Re: [RFC PATCH v3 1/3] mm, x86: support copying a folio using non-temporal stores

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] x86/mm: missing KCFI_REFERENCE() for copy_mc_page_nt()
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commit c8614f6dfdf00a57c43828a75e8413d839e5a48b
Author: Huan Nguyen <nhuhuan@google.com>

mm, x86: support copying a folio using non-temporal stores

This commit adds copy_mc_page_nt(), copy_mc_highpage_nt(), and
folio_mc_copy_nt() to support machine-check safe copying of folios on x86_64
using non-temporal stores.

> diff --git a/arch/x86/include/asm/page_64.h b/arch/x86/include/asm/page_64.h
> index 1895c207f629a..f37126b562390 100644
> --- a/arch/x86/include/asm/page_64.h
> +++ b/arch/x86/include/asm/page_64.h
> @@ -114,7 +114,9 @@ static inline void clear_page(void *addr)
>  	clear_pages(addr, 1);
>  }
>  
> +#define __HAVE_ARCH_COPY_PAGE_NT 1
>  void copy_page(void *to, void *from);
> +unsigned long copy_mc_page_nt(void *to, const void *from);
>  KCFI_REFERENCE(copy_page);

[Severity: Low]
In arch/x86/lib/copy_page_64.S, copy_mc_page_nt() is defined using
SYM_TYPED_FUNC_START(copy_mc_page_nt) and exported from assembly via
EXPORT_SYMBOL_GPL(copy_mc_page_nt):

arch/x86/lib/copy_page_64.S:
    SYM_TYPED_FUNC_START(copy_mc_page_nt)
    ...
    SYM_FUNC_END(copy_mc_page_nt)
    EXPORT_SYMBOL_GPL(copy_mc_page_nt)

When CONFIG_CFI_CLANG is enabled, SYM_TYPED_FUNC_START(copy_mc_page_nt) emits
a relocation against __kcfi_typeid_copy_mc_page_nt. Because Clang only emits
__kcfi_typeid_<func> symbols in C translation units where the function has its
address taken, and EXPORT_SYMBOL_GPL() in an assembly file does not include
the C-only __ADDRESSABLE() annotation, nothing in C takes the address of
copy_mc_page_nt() (which is only called directly from copy_mc_highpage_nt() in
include/linux/highmem.h).

Will building with CONFIG_CFI_CLANG=y fail at link time with an undefined
reference to __kcfi_typeid_copy_mc_page_nt unless
KCFI_REFERENCE(copy_mc_page_nt) is added alongside KCFI_REFERENCE(copy_page)
in arch/x86/include/asm/page_64.h?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261103223025.2482227-1-nhuhuan@google.com?part=1