linux-kernel - Re: [PATCHv5 15/16] x86/mm: Introduce kernel_ident_mapping

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Date: Mon, 8 Jan 2024 03:13:06 +0000
From: "Huang, Kai" <kai.huang@...el.com>
To: "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>, "mingo@...hat.com"
	<mingo@...hat.com>, "x86@...nel.org" <x86@...nel.org>, "bp@...en8.de"
	<bp@...en8.de>, "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>
CC: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>, "Reshetova, Elena"
	<elena.reshetova@...el.com>, "Nakajima, Jun" <jun.nakajima@...el.com>,
	"rafael@...nel.org" <rafael@...nel.org>, "peterz@...radead.org"
	<peterz@...radead.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "sathyanarayanan.kuppuswamy@...ux.intel.com"
	<sathyanarayanan.kuppuswamy@...ux.intel.com>, "Hunter, Adrian"
	<adrian.hunter@...el.com>, "thomas.lendacky@....com"
	<thomas.lendacky@....com>, "ashish.kalra@....com" <ashish.kalra@....com>,
	"kexec@...ts.infradead.org" <kexec@...ts.infradead.org>, "seanjc@...gle.com"
	<seanjc@...gle.com>, "bhe@...hat.com" <bhe@...hat.com>,
	"linux-coco@...ts.linux.dev" <linux-coco@...ts.linux.dev>
Subject: Re: [PATCHv5 15/16] x86/mm: Introduce kernel_ident_mapping_free()

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@...ux.intel.com>
> ---
>  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@...el.com>