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 S933427AbdLRU6J (ORCPT <rfc822;w@1wt.eu>);
        Mon, 18 Dec 2017 15:58:09 -0500
Received: from merlin.infradead.org ([205.233.59.134]:44394 "EHLO
        merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1757558AbdLRU6H (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Mon, 18 Dec 2017 15:58:07 -0500
Date: Mon, 18 Dec 2017 21:57:32 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Dave Hansen <dave.hansen@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
        LKML <linux-kernel@vger.kernel.org>, x86@kernel.org,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andy Lutomirsky <luto@kernel.org>, Borislav Petkov <bpetkov@suse.de>,
        Greg KH <gregkh@linuxfoundation.org>, keescook@google.com,
        hughd@google.com, Brian Gerst <brgerst@gmail.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Denys Vlasenko <dvlasenk@redhat.com>, Rik van Riel <riel@redhat.com>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Juergen Gross <jgross@suse.com>,
        David Laight <David.Laight@aculab.com>,
        Eduardo Valentin <eduval@amazon.com>, aliguori@amazon.com,
        Will Deacon <will.deacon@arm.com>, daniel.gruss@iaik.tugraz.at,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Ingo Molnar <mingo@kernel.org>, Borislav Petkov <bp@suse.de>,
        "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [patch V163 27/51] x86/mm/pti: Populate user PGD
Message-ID: <20171218205732.ql7ejvd743hceotf@hirez.programming.kicks-ass.net>
References: <20171218114215.239543034@linutronix.de>
 <20171218115255.827361623@linutronix.de>
 <93e88e2c-50fc-49a6-7113-d9b64cf70fbd@intel.com>
 <20171218204105.bs74dkixlbwfegb5@hirez.programming.kicks-ass.net>
 <e34cfd7a-73d3-f9a7-1940-6b6a892a5fe9@intel.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <e34cfd7a-73d3-f9a7-1940-6b6a892a5fe9@intel.com>
User-Agent: NeoMutt/20170609 (1.8.3)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Mon, Dec 18, 2017 at 12:45:13PM -0800, Dave Hansen wrote:
> On 12/18/2017 12:41 PM, Peter Zijlstra wrote:
> >> I also don't think the user_shared area of the fixmap can get *that*
> >> big.  Does anybody know offhand what the theoretical limits are there?
> > Problem there is the nr_cpus term I think, we currently have up to 8k
> > CPUs, but I can see that getting bigger in the future.
> 
> It only matters if we go over 512GB, though.  Is the per-cpu part of the
> fixmap ever more than 512GB/8k=64MB?

Unlikely, I think the LDT (@ 32 pages / 128K) and the DS (@ 2*4 pages /
32K) are the largest entries in there.