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

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Date:	Wed, 12 Mar 2014 15:59:58 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Stefani Seibold <stefani@...bold.net>,
	Greg KH <gregkh@...uxfoundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	X86 ML <x86@...nel.org>, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Andi Kleen <ak@...ux.intel.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	John Stultz <john.stultz@...aro.org>,
	Pavel Emelyanov <xemul@...allels.com>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	andriy.shevchenko@...ux.intel.com,
	Martin Runge <Martin.Runge@...de-schwarz.com>,
	Andreas Brief <Andreas.Brief@...de-schwarz.com>
Subject: Re: [PATCH 3/3] x86, vdso32: handle 32 bit vDSO larger one page

On Wed, Mar 12, 2014 at 3:58 PM, H. Peter Anvin <hpa@...or.com> wrote:
> 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.

Note that this code is completely unnecessary if either of my patch
sets is accepted.  Since you're the maintainer, can you give an
opinion? :)

--Andy
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