linux-kernel - Re: [PATCH v9 03/18] arm64: trans_pgd: make trans_pgd_map

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Message-ID: <c857d4aa-e8ec-81f6-bdea-dff6513c52dc@arm.com>
Date:   Wed, 29 Apr 2020 18:01:02 +0100
From:   James Morse <james.morse@....com>
To:     Pavel Tatashin <pasha.tatashin@...een.com>
Cc:     jmorris@...ei.org, sashal@...nel.org, ebiederm@...ssion.com,
        kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
        corbet@....net, catalin.marinas@....com, will@...nel.org,
        linux-arm-kernel@...ts.infradead.org, maz@...nel.org,
        vladimir.murzin@....com, matthias.bgg@...il.com,
        bhsharma@...hat.com, linux-mm@...ck.org, mark.rutland@....com,
        steve.capper@....com, rfontana@...hat.com, tglx@...utronix.de,
        selindag@...il.com
Subject: Re: [PATCH v9 03/18] arm64: trans_pgd: make trans_pgd_map_page
 generic

Hi Pavel,

On 26/03/2020 03:24, Pavel Tatashin wrote:
> kexec is going to use a different allocator, so make

> trans_pgd_map_page to accept allocator as an argument, and also
> kexec is going to use a different map protection, so also pass
> it via argument.

This trans_pgd_map_page() used to be create_single_mapping() It creates page tables that
map one page: the relocation code.

Why do you need a different pgprot? Surely PAGE_KERNEL_EXEC is exactly what you want.


> diff --git a/arch/arm64/include/asm/trans_pgd.h b/arch/arm64/include/asm/trans_pgd.h
> index 23153c13d1ce..ad5194ad178d 100644
> --- a/arch/arm64/include/asm/trans_pgd.h
> +++ b/arch/arm64/include/asm/trans_pgd.h
> @@ -12,10 +12,24 @@
>  #include <linux/types.h>
>  #include <asm/pgtable-types.h>
>  
> +/*
> + * trans_alloc_page
> + *	- Allocator that should return exactly one zeroed page, if this
> + *	 allocator fails, trans_pgd returns -ENOMEM error.

trans_pgd is what you pass in to trans_pgd_map_page() or trans_pgd_create_copy().
Do you mean what those functions return?


> + *
> + * trans_alloc_arg
> + *	- Passed to trans_alloc_page as an argument
> + */

> diff --git a/arch/arm64/kernel/hibernate.c b/arch/arm64/kernel/hibernate.c
> index 3d6f0fd73591..607bb1fbc349 100644
> --- a/arch/arm64/kernel/hibernate.c
> +++ b/arch/arm64/kernel/hibernate.c
> @@ -195,6 +200,11 @@ static int create_safe_exec_page(void *src_start, size_t length,
>  				 unsigned long dst_addr,
>  				 phys_addr_t *phys_dst_addr)
>  {
> +	struct trans_pgd_info trans_info = {
> +		.trans_alloc_page	= hibernate_page_alloc,
> +		.trans_alloc_arg	= (void *)GFP_ATOMIC,
> +	};

As you need another copy of this in the next patch, is it worth declaring this globally
and making it const?


> diff --git a/arch/arm64/mm/trans_pgd.c b/arch/arm64/mm/trans_pgd.c
> index d20e48520cef..275a79935d7e 100644
> --- a/arch/arm64/mm/trans_pgd.c
> +++ b/arch/arm64/mm/trans_pgd.c
> @@ -180,8 +185,18 @@ int trans_pgd_create_copy(pgd_t **dst_pgdp, unsigned long start,
>  	return rc;
>  }
>  
> -int trans_pgd_map_page(pgd_t *trans_pgd, void *page, unsigned long dst_addr,
> -		       pgprot_t pgprot)
> +/*
> + * Add map entry to trans_pgd for a base-size page at PTE level.
> + * info:	contains allocator and its argument
> + * trans_pgd:	page table in which new map is added.
> + * page:	page to be mapped.

> + * dst_addr:	new VA address for the pages

~s/pages/page/

This thing only maps one page.


> + * pgprot:	protection for the page.
> + *
> + * Returns 0 on success, and -ENOMEM on failure.
> + */
> +int trans_pgd_map_page(struct trans_pgd_info *info, pgd_t *trans_pgd,
> +		       void *page, unsigned long dst_addr, pgprot_t pgprot)
>  {
>  	pgd_t *pgdp;
>  	pud_t *pudp;



Thanks,

James