From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f50.google.com (mail-pa0-f50.google.com [209.85.220.50]) by kanga.kvack.org (Postfix) with ESMTP id 84F296B0037 for ; Tue, 15 Jul 2014 19:46:58 -0400 (EDT) Received: by mail-pa0-f50.google.com with SMTP id et14so176115pad.9 for ; Tue, 15 Jul 2014 16:46:58 -0700 (PDT) Received: from mail.zytor.com (terminus.zytor.com. [2001:1868:205::10]) by mx.google.com with ESMTPS id cc2si12891864pbc.255.2014.07.15.16.46.57 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 15 Jul 2014 16:46:57 -0700 (PDT) Message-ID: <53C5BD3E.2010600@zytor.com> Date: Tue, 15 Jul 2014 16:46:06 -0700 From: "H. Peter Anvin" MIME-Version: 1.0 Subject: Re: [RFC PATCH 3/11] x86, mm, pat: Change reserve_memtype() to handle WT type References: <1405452884-25688-1-git-send-email-toshi.kani@hp.com> <1405452884-25688-4-git-send-email-toshi.kani@hp.com> <1405465801.28702.34.camel@misato.fc.hp.com> In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Andy Lutomirski , Toshi Kani Cc: Thomas Gleixner , Ingo Molnar , Andrew Morton , Arnd Bergmann , Konrad Rzeszutek Wilk , plagnioj@jcrosoft.com, tomi.valkeinen@ti.com, "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , Stefan Bader , Dave Airlie , Borislav Petkov On 07/15/2014 04:36 PM, Andy Lutomirski wrote: > On Tue, Jul 15, 2014 at 4:10 PM, Toshi Kani wrote: >> On Tue, 2014-07-15 at 12:56 -0700, Andy Lutomirski wrote: >>> On Tue, Jul 15, 2014 at 12:34 PM, Toshi Kani wrote: >>>> This patch changes reserve_memtype() to handle the new WT type. >>>> When (!pat_enabled && new_type), it continues to set either WB >>>> or UC- to *new_type. When pat_enabled, it can reserve a given >>>> non-RAM range for WT. At this point, it may not reserve a RAM >>>> range for WT since reserve_ram_pages_type() uses the page flags >>>> limited to three memory types, WB, WC and UC. >>> >>> FWIW, last time I looked at this, it seemed like all the fancy >>> reserve_ram_pages stuff was unnecessary: shouldn't the RAM type be >>> easy to track in the direct map page tables? >> >> Are you referring the direct map page tables as the kernel page >> directory tables (pgd/pud/..)? >> >> I think it needs to be able to keep track of the memory type per a >> physical memory range, not per a translation, in order to prevent >> aliasing of the memory type. > > Actual RAM (the lowmem kind, which is all of it on x86_64) is mapped > linearly somewhere in kernel address space. The pagetables for that > mapping could be used as the canonical source of the memory type for > the ram range in question. > > This only works for lowmem, so maybe it's not a good idea to rely on it. > We could do that, but would it be better? -hpa -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org