Re: [PATCH v2] powerpc/s64: Clarify that radix lacks DEBUG_PAGEALLOC

[Christophe Leroy <christophe.leroy@csgroup.eu>]

Le 13/10/2021 à 23:34, Joel Stanley a écrit :
> The page_alloc.c code will call into __kernel_map_pages when
> DEBUG_PAGEALLOC is configured and enabled.
> 
> As the implementation assumes hash, this should crash spectacularly if
> not for a bit of luck in __kernel_map_pages. In this function
> linear_map_hash_count is always zero, the for loop exits without doing
> any damage.
> 
> There are no other platforms that determine if they support
> debug_pagealloc at runtime. Instead of adding code to mm/page_alloc.c to
> do that, this change turns the map/unmap into a noop when in radix
> mode and prints a warning once.
> 
> Signed-off-by: Joel Stanley <joel@jms.id.au>
> ---
> v2: Put __kernel_map_pages in pgtable.h
> 
>   arch/powerpc/include/asm/book3s/64/hash.h    |  2 ++
>   arch/powerpc/include/asm/book3s/64/pgtable.h | 11 +++++++++++
>   arch/powerpc/include/asm/book3s/64/radix.h   |  3 +++
>   arch/powerpc/mm/book3s64/hash_utils.c        |  2 +-
>   arch/powerpc/mm/book3s64/radix_pgtable.c     |  7 +++++++
>   5 files changed, 24 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/include/asm/book3s/64/hash.h b/arch/powerpc/include/asm/book3s/64/hash.h
> index d959b0195ad9..674fe0e890dc 100644
> --- a/arch/powerpc/include/asm/book3s/64/hash.h
> +++ b/arch/powerpc/include/asm/book3s/64/hash.h
> @@ -255,6 +255,8 @@ int hash__create_section_mapping(unsigned long start, unsigned long end,
>   				 int nid, pgprot_t prot);
>   int hash__remove_section_mapping(unsigned long start, unsigned long end);
>   
> +void hash__kernel_map_pages(struct page *page, int numpages, int enable);
> +
>   #endif /* !__ASSEMBLY__ */
>   #endif /* __KERNEL__ */
>   #endif /* _ASM_POWERPC_BOOK3S_64_HASH_H */
> diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h
> index 5d34a8646f08..265661ded238 100644
> --- a/arch/powerpc/include/asm/book3s/64/pgtable.h
> +++ b/arch/powerpc/include/asm/book3s/64/pgtable.h
> @@ -1101,6 +1101,17 @@ static inline void vmemmap_remove_mapping(unsigned long start,
>   }
>   #endif
>   
> +#ifdef CONFIG_DEBUG_PAGEALLOC
> +static inline void __kernel_map_pages(struct page *page, int numpages, int enable)
> +{
> +	if (radix_enabled()) {
> +		radix__kernel_map_pages(page, numpages, enable);
> +		return;
> +	}
> +	hash__kernel_map_pages(page, numpages, enable);

I'd have prefered something like below

	if (radix_enabled())
		radix__kernel_map_pages(page, numpages, enable);
	else
		hash__kernel_map_pages(page, numpages, enable);


But regardless,

Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>



> +}
> +#endif
> +
>   static inline pte_t pmd_pte(pmd_t pmd)
>   {
>   	return __pte_raw(pmd_raw(pmd));
> diff --git a/arch/powerpc/include/asm/book3s/64/radix.h b/arch/powerpc/include/asm/book3s/64/radix.h
> index 59cab558e2f0..d090d9612348 100644
> --- a/arch/powerpc/include/asm/book3s/64/radix.h
> +++ b/arch/powerpc/include/asm/book3s/64/radix.h
> @@ -316,5 +316,8 @@ int radix__create_section_mapping(unsigned long start, unsigned long end,
>   				  int nid, pgprot_t prot);
>   int radix__remove_section_mapping(unsigned long start, unsigned long end);
>   #endif /* CONFIG_MEMORY_HOTPLUG */
> +
> +void radix__kernel_map_pages(struct page *page, int numpages, int enable);
> +
>   #endif /* __ASSEMBLY__ */
>   #endif
> diff --git a/arch/powerpc/mm/book3s64/hash_utils.c b/arch/powerpc/mm/book3s64/hash_utils.c
> index c145776d3ae5..cfd45245d009 100644
> --- a/arch/powerpc/mm/book3s64/hash_utils.c
> +++ b/arch/powerpc/mm/book3s64/hash_utils.c
> @@ -1988,7 +1988,7 @@ static void kernel_unmap_linear_page(unsigned long vaddr, unsigned long lmi)
>   				     mmu_kernel_ssize, 0);
>   }
>   
> -void __kernel_map_pages(struct page *page, int numpages, int enable)
> +void hash__kernel_map_pages(struct page *page, int numpages, int enable)
>   {
>   	unsigned long flags, vaddr, lmi;
>   	int i;
> diff --git a/arch/powerpc/mm/book3s64/radix_pgtable.c b/arch/powerpc/mm/book3s64/radix_pgtable.c
> index ae20add7954a..83b33418ad28 100644
> --- a/arch/powerpc/mm/book3s64/radix_pgtable.c
> +++ b/arch/powerpc/mm/book3s64/radix_pgtable.c
> @@ -920,6 +920,13 @@ void __meminit radix__vmemmap_remove_mapping(unsigned long start, unsigned long
>   #endif
>   #endif
>   
> +#ifdef CONFIG_DEBUG_PAGEALLOC
> +void radix__kernel_map_pages(struct page *page, int numpages, int enable)
> +{
> +        pr_warn_once("DEBUG_PAGEALLOC not supported in radix mode\n");
> +}
> +#endif
> +
>   #ifdef CONFIG_TRANSPARENT_HUGEPAGE
>   
>   unsigned long radix__pmd_hugepage_update(struct mm_struct *mm, unsigned long addr,
>