linux-kernel - Re: [PATCH 1/2] x86/arch_prctl: add ARCH_SET_{COMPAT,NATIVE} to change compatible mode

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Message-ID: <CAJwJo6b=17Q7L-ryqpsXTMoaL9UP1U-gPK0Cm8Oy+r=-OTE=Dg@mail.gmail.com>
Date:	Sat, 9 Apr 2016 11:06:08 +0300
From:	Dmitry Safonov <0x7f454c46@...il.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Dmitry Safonov <dsafonov@...tuozzo.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Shuah Khan <shuahkh@....samsung.com>,
	Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Borislav Petkov <bp@...en8.de>, khorenko@...tuozzo.com,
	X86 ML <x86@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>, xemul@...tuozzo.com,
	linux-kselftest@...r.kernel.org,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH 1/2] x86/arch_prctl: add ARCH_SET_{COMPAT,NATIVE} to
 change compatible mode

2016-04-08 23:44 GMT+03:00 Andy Lutomirski <luto@...capital.net>:
> On Apr 8, 2016 9:20 AM, "Dmitry Safonov" <dsafonov@...tuozzo.com> wrote:
>>
>>
>> And if it's not there - return error?
>
> No, just leave IP unchanged.

Ok, will resend with this fixup.

>
> Feel free to ask for help on some of these details.  user_64bit_mode
> will be helpful too.

Thanks.

>> I doubt, is it sane to remove
>> TS_COMPAT instead, leaving TIF_IA32, as for some cases
>> we need to know if task is compatible outside of syscall's path?
>
> No.  TS_COMPAT is important, and it's also better behaved than
> TIF_IA32 -- it has a very specific meaning: "am I currently executing
> a 32-bit syscall".
>
>
> The comment is wrong :). TS_COMPAT is true on int80 or 32-bit vdso
> syscall entries and is false otherwise.  64-bit tasks can use int80
> and, with your patches, will be able to use the 32-bit vdso entry as
> well.
>

Oh, yes, I see what you pointing, thanks, will work on it.