linux-kernel - Re: [PATCH 3/3] x86, vdso32: handle 32 bit vDSO larger one page

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Date:	Wed, 12 Mar 2014 15:58:17 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Stefani Seibold <stefani@...bold.net>, gregkh@...uxfoundation.org,
	linux-kernel@...r.kernel.org, x86@...nel.org, tglx@...utronix.de,
	mingo@...hat.com, ak@...ux.intel.com, aarcange@...hat.com,
	john.stultz@...aro.org, luto@...capital.net, xemul@...allels.com,
	gorcunov@...nvz.org, andriy.shevchenko@...ux.intel.com
CC:	Martin.Runge@...de-schwarz.com, Andreas.Brief@...de-schwarz.com
Subject: Re: [PATCH 3/3] x86, vdso32: handle 32 bit vDSO larger one page

On 03/12/2014 03:51 PM, Stefani Seibold wrote:
> This patch enables 32 bit vDSO which are larger than a page. Currently
> two pages are reserved, this should be enough for future improvements.
> 
> Signed-off-by: Stefani Seibold <stefani@...bold.net>
> ---
>  arch/x86/include/asm/fixmap.h |  4 +++-
>  arch/x86/vdso/vdso32-setup.c  | 29 +++++++++++++++++++----------
>  2 files changed, 22 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/x86/include/asm/fixmap.h b/arch/x86/include/asm/fixmap.h
> index 094d0cc..f513f14 100644
> --- a/arch/x86/include/asm/fixmap.h
> +++ b/arch/x86/include/asm/fixmap.h
> @@ -43,6 +43,8 @@ extern unsigned long __FIXADDR_TOP;
>  
>  #define FIXADDR_USER_START     __fix_to_virt(FIX_VDSO)
>  #define FIXADDR_USER_END       __fix_to_virt(FIX_VDSO - 1)
> +
> +#define MAX_VDSO_PAGES	2
>  #else
>  #define FIXADDR_TOP	(VSYSCALL_END-PAGE_SIZE)
>  
> @@ -74,7 +76,7 @@ extern unsigned long __FIXADDR_TOP;
>  enum fixed_addresses {
>  #ifdef CONFIG_X86_32
>  	FIX_HOLE,
> -	FIX_VDSO,
> +	FIX_VDSO = MAX_VDSO_PAGES,
>  	VVAR_PAGE,
>  	VSYSCALL_HPET,

Can we make this FIX_HOLE + MAX_VDSO_PAGES or at least a comment
explaning the constraint here... otherwise I fear random breakage.

> +	for(i = 0; i != vdso32_size; ++i)
> +		vdso32_pages[i] = virt_to_page(vdso_pages + VDSO_OFFSET(i));

Stylistic note:

	for (i = 0; i < vdso32_size; i++)

Otherwise it really seems simple enough.

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