Re: [PATCHv5 15/16] x86/mm: Introduce kernel_ident_mapping_free()

[Huang, Kai]

On Sat, 2023-12-23 at 02:52 +0300, Kirill A. Shutemov wrote:
> The helper complements kernel_ident_mapping_init(): it frees the
> identity mapping that was previously allocated. It will be used in the
> error path to free a partially allocated mapping or if the mapping is no
> longer needed.
> 
> The caller provides a struct x86_mapping_info with the free_pgd_page()
> callback hooked up and the pgd_t to free.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> ---
>  arch/x86/include/asm/init.h |  3 ++
>  arch/x86/mm/ident_map.c     | 73 +++++++++++++++++++++++++++++++++++++
>  2 files changed, 76 insertions(+)
> 
> diff --git a/arch/x86/include/asm/init.h b/arch/x86/include/asm/init.h
> index cc9ccf61b6bd..14d72727d7ee 100644
> --- a/arch/x86/include/asm/init.h
> +++ b/arch/x86/include/asm/init.h
> @@ -6,6 +6,7 @@
>  
>  struct x86_mapping_info {
>  	void *(*alloc_pgt_page)(void *); /* allocate buf for page table */
> +	void (*free_pgt_page)(void *, void *); /* free buf for page table */
>  	void *context;			 /* context for alloc_pgt_page */
>  	unsigned long page_flag;	 /* page flag for PMD or PUD entry */
>  	unsigned long offset;		 /* ident mapping offset */
> @@ -16,4 +17,6 @@ struct x86_mapping_info {
>  int kernel_ident_mapping_init(struct x86_mapping_info *info, pgd_t *pgd_page,
>  				unsigned long pstart, unsigned long pend);
>  
> +void kernel_ident_mapping_free(struct x86_mapping_info *info, pgd_t *pgd);

Maybe range-based free function can provide more flexibility (e.g., you can
directly call the free function to cleanup in kernel_ident_mapping_init()
internally when something goes wrong), but I guess this is sufficient for
current use case (and perhaps the majority use cases).

Reviewed-by: Kai Huang <kai.huang@xxxxxxxxx>