linux-kernel - Re: [PATCH] mm: consolidate pgtable_cache_init() and pgd_cache

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Message-ID: <20190821154942.js4u466rolnekwmq@willie-the-truck>
Date:   Wed, 21 Aug 2019 16:49:42 +0100
From:   Will Deacon <will@...nel.org>
To:     Mike Rapoport <rppt@...ux.ibm.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: consolidate pgtable_cache_init() and pgd_cache_init()

On Wed, Aug 21, 2019 at 06:06:58PM +0300, Mike Rapoport wrote:
> Both pgtable_cache_init() and pgd_cache_init() are used to initialize kmem
> cache for page table allocations on several architectures that do not use
> PAGE_SIZE tables for one or more levels of the page table hierarchy.
> 
> Most architectures do not implement these functions and use __week default
> NOP implementation of pgd_cache_init(). Since there is no such default for
> pgtable_cache_init(), its empty stub is duplicated among most
> architectures.
> 
> Rename the definitions of pgd_cache_init() to pgtable_cache_init() and drop
> empty stubs of pgtable_cache_init().
> 
> Signed-off-by: Mike Rapoport <rppt@...ux.ibm.com>
> ---

[...]

> diff --git a/arch/arm64/mm/pgd.c b/arch/arm64/mm/pgd.c
> index 7548f9c..4a64089 100644
> --- a/arch/arm64/mm/pgd.c
> +++ b/arch/arm64/mm/pgd.c
> @@ -35,7 +35,7 @@ void pgd_free(struct mm_struct *mm, pgd_t *pgd)
>  		kmem_cache_free(pgd_cache, pgd);
>  }
>  
> -void __init pgd_cache_init(void)
> +void __init pgtable_cache_init(void)
>  {
>  	if (PGD_SIZE == PAGE_SIZE)
>  		return;

[...]

> diff --git a/init/main.c b/init/main.c
> index b90cb5f..2fa8038 100644
> --- a/init/main.c
> +++ b/init/main.c
> @@ -507,7 +507,7 @@ void __init __weak mem_encrypt_init(void) { }
>  
>  void __init __weak poking_init(void) { }
>  
> -void __init __weak pgd_cache_init(void) { }
> +void __init __weak pgtable_cache_init(void) { }
>  
>  bool initcall_debug;
>  core_param(initcall_debug, initcall_debug, bool, 0644);
> @@ -565,7 +565,6 @@ static void __init mm_init(void)
>  	init_espfix_bsp();
>  	/* Should be run after espfix64 is set up. */
>  	pti_init();
> -	pgd_cache_init();
>  }

AFAICT, this change means we now initialise our pgd cache before
debug_objects_mem_init() has run. Is that going to cause fireworks with
CONFIG_DEBUG_OBJECTS when we later free a pgd?

Will