linux-kernel - Re: [PATCHv2 2/5] x86/mm: introduce mmap_{,legacy}

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Message-ID: <69eecbfb-9d39-9c72-7ec3-68fdbea45245@virtuozzo.com>
Date:   Wed, 18 Jan 2017 14:26:37 +0300
From:   Dmitry Safonov <dsafonov@...tuozzo.com>
To:     Andy Lutomirski <luto@...capital.net>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Dmitry Safonov <0x7f454c46@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...e.de>, X86 ML <x86@...nel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCHv2 2/5] x86/mm: introduce mmap_{,legacy}_base

On 01/17/2017 11:27 PM, Andy Lutomirski wrote:
> On Mon, Jan 16, 2017 at 4:33 AM, Dmitry Safonov <dsafonov@...tuozzo.com> wrote:
>> In the following patch they will be used to compute:
>> - mmap_base in compat sys_mmap() in native 64-bit binary
>> and vice-versa
>> - mmap_base for native sys_mmap() in compat x32/ia32-bit binary.
>
> I may be wrong here, but I suspect that you're repeating something
> that I consider to be a mistake that's all over the x86 code.
> Specifically, you're distinguishing "native" from "compat" instead of
> "32-bit" from "64-bit".  If you did the latter, then you wouldn't need
> the "native" case to work differently on 32-bit kernels vs 64-bit
> kernels, I think.  Would making this change make your code simpler?
>
> The x86 signal code is the worst offender IMO.

Yes, I also don't like to differ them especially by TIF_ADDR32 flag.
I did distinguishing for the reason that I needed to know for which
task 64/32-bit was computed mm->mmap_base.
Otherwise I could introduce mm->mmap_compat_base and don't differ
tasks by TIF_ADDR32 flag - only by in_compat_syscall(), but that
would change mm_struct generic code (adding a field to mm).
So, I thought it may have more opposition to add a field to mm
in generic code and fixed it here, in x86.

>
> --Andy
>

-- 
              Dmitry