From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1756511AbdKNUaE (ORCPT <rfc822;w@1wt.eu>);
        Tue, 14 Nov 2017 15:30:04 -0500
Received: from Galois.linutronix.de ([146.0.238.70]:39031 "EHLO
        Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1756021AbdKNU3z (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Tue, 14 Nov 2017 15:29:55 -0500
Date: Tue, 14 Nov 2017 21:29:41 +0100 (CET)
From: Thomas Gleixner <tglx@linutronix.de>
To: "Kirill A. Shutemov" <kirill@shutemov.name>
cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Ingo Molnar <mingo@redhat.com>, x86@kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andy Lutomirski <luto@amacapital.net>,
        Nicholas Piggin <npiggin@gmail.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCHv2 1/2] x86/mm: Do not allow non-MAP_FIXED mapping across
 DEFAULT_MAP_WINDOW border
In-Reply-To: <20171114192113.t7pq5p2n5emmiw2n@node.shutemov.name>
Message-ID: <alpine.DEB.2.20.1711142128170.2221@nanos>
References: <20171114134322.40321-1-kirill.shutemov@linux.intel.com> <alpine.DEB.2.20.1711141630210.2044@nanos> <20171114192113.t7pq5p2n5emmiw2n@node.shutemov.name>
User-Agent: Alpine 2.20 (DEB 67 2015-01-07)
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
X-Linutronix-Spam-Score: -1.0
X-Linutronix-Spam-Level: -
X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required,  ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Tue, 14 Nov 2017, Kirill A. Shutemov wrote:
> On Tue, Nov 14, 2017 at 05:01:50PM +0100, Thomas Gleixner wrote:
> > +bool mmap_address_hint_valid(unsigned long addr, unsigned long len)
> > +{
> > +	if (TASK_SIZE - len < addr)
> > +		return false;
> > +#if CONFIG_PGTABLE_LEVELS >= 5
> > +	return (addr > DEFAULT_MAP_WINDOW) == (addr + len > DEFAULT_MAP_WINDOW);
> 
> Is it micro optimization? I don't feel it necessary. It's not that hot
> codepath to care about few cycles. (And one more place to care about for
> boot-time switching.)
> 
> If you think it's needed, maybe IS_ENABLED() instead?

You're right. It's can be unconditional, For page table levels < 5 its just
redundant as its covered by the TASK_SIZE check already.

Thanks,

	tglx