linux-kernel - Re: [PATCH 5/9] x86/clear_pages: add clear

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Message-ID: <20230406082304.GE386572@hirez.programming.kicks-ass.net>
Date:   Thu, 6 Apr 2023 10:23:04 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Ankur Arora <ankur.a.arora@...cle.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org, x86@...nel.org,
        torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
        luto@...nel.org, bp@...en8.de, dave.hansen@...ux.intel.com,
        hpa@...or.com, mingo@...hat.com, juri.lelli@...hat.com,
        willy@...radead.org, mgorman@...e.de, rostedt@...dmis.org,
        tglx@...utronix.de, vincent.guittot@...aro.org, jon.grimm@....com,
        bharata@....com, boris.ostrovsky@...cle.com, konrad.wilk@...cle.com
Subject: Re: [PATCH 5/9] x86/clear_pages: add clear_pages()

On Sun, Apr 02, 2023 at 10:22:29PM -0700, Ankur Arora wrote:
> Add clear_pages() and define the ancillary clear_user_pages().
> 
> Signed-off-by: Ankur Arora <ankur.a.arora@...cle.com>
> ---
>  arch/x86/include/asm/page.h    | 6 ++++++
>  arch/x86/include/asm/page_32.h | 6 ++++++
>  arch/x86/include/asm/page_64.h | 9 +++++++--
>  3 files changed, 19 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/include/asm/page.h b/arch/x86/include/asm/page.h
> index d18e5c332cb9..03e3c69fc427 100644
> --- a/arch/x86/include/asm/page.h
> +++ b/arch/x86/include/asm/page.h
> @@ -28,6 +28,12 @@ static inline void clear_user_page(void *page, unsigned long vaddr,
>  	clear_page(page);
>  }
>  
> +static inline void clear_user_pages(void *page, unsigned long vaddr,
> +				    struct page *pg, unsigned int nsubpages)
> +{
> +	clear_pages(page, nsubpages);
> +}

This seems dodgy, clear_user* has slightly different semantics. It needs
the access_ok() and stac/clac thing on at the very least.

> +
>  static inline void copy_user_page(void *to, void *from, unsigned long vaddr,
>  				  struct page *topage)
>  {
> diff --git a/arch/x86/include/asm/page_32.h b/arch/x86/include/asm/page_32.h
> index 580d71aca65a..3523d1150cfc 100644
> --- a/arch/x86/include/asm/page_32.h
> +++ b/arch/x86/include/asm/page_32.h
> @@ -22,6 +22,12 @@ static inline void clear_page(void *page)
>  	memset(page, 0, PAGE_SIZE);
>  }
>  
> +static inline void clear_pages(void *page, unsigned int nsubpages)
> +{
> +	for (int i = 0; i < nsubpages; i++)
> +		clear_page(page + i * PAGE_SIZE);

cond_resched() ?

> +}
> +
>  static inline void copy_page(void *to, void *from)
>  {
>  	memcpy(to, from, PAGE_SIZE);