From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi0-f49.google.com (mail-oi0-f49.google.com [209.85.218.49]) by kanga.kvack.org (Postfix) with ESMTP id 09C3E6B0071 for ; Mon, 3 Nov 2014 13:02:02 -0500 (EST) Received: by mail-oi0-f49.google.com with SMTP id u20so8966375oif.22 for ; Mon, 03 Nov 2014 10:02:01 -0800 (PST) Received: from g4t3426.houston.hp.com (g4t3426.houston.hp.com. [15.201.208.54]) by mx.google.com with ESMTPS id dm7si18964433oeb.48.2014.11.03.10.02.00 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Mon, 03 Nov 2014 10:02:00 -0800 (PST) Message-ID: <1415036879.29109.26.camel@misato.fc.hp.com> Subject: Re: [PATCH v4 1/7] x86, mm, pat: Set WT to PA7 slot of PAT MSR From: Toshi Kani Date: Mon, 03 Nov 2014 10:47:59 -0700 In-Reply-To: References: <1414450545-14028-1-git-send-email-toshi.kani@hp.com> <1414450545-14028-2-git-send-email-toshi.kani@hp.com> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Thomas Gleixner Cc: hpa@zytor.com, mingo@redhat.com, akpm@linux-foundation.org, arnd@arndb.de, linux-mm@kvack.org, linux-kernel@vger.kernel.org, jgross@suse.com, stefan.bader@canonical.com, luto@amacapital.net, hmh@hmh.eng.br, yigal@plexistor.com, konrad.wilk@oracle.com On Mon, 2014-11-03 at 18:14 +0100, Thomas Gleixner wrote: > On Mon, 27 Oct 2014, Toshi Kani wrote: > > + } else { > > + /* > > + * PAT full support. WT is set to slot 7, which minimizes > > + * the risk of using the PAT bit as slot 3 is UC and is > > + * currently unused. Slot 4 should remain as reserved. > > This comment makes no sense. What minimizes which risk and what has > this to do with slot 3 and slot 4? This is for precaution. Since the patch enables the PAT bit the first time, it was suggested that we keep slot 4 reserved and set it to WB. The PAT bit still has no effect to slot 0/1/2 (WB/WC/UC-) after this patch. Slot 7 is the safest slot since slot 3 (UC) is unused today. https://lkml.org/lkml/2014/9/4/691 https://lkml.org/lkml/2014/9/5/394 > > + * > > + * PTE encoding used in Linux: > > + * PAT > > + * |PCD > > + * ||PWT PAT > > + * ||| slot > > + * 000 0 WB : _PAGE_CACHE_MODE_WB > > + * 001 1 WC : _PAGE_CACHE_MODE_WC > > + * 010 2 UC-: _PAGE_CACHE_MODE_UC_MINUS > > + * 011 3 UC : _PAGE_CACHE_MODE_UC > > + * 100 4 > > + * 101 5 > > + * 110 6 > > Well, they are still mapped to WB/WC/UC_MINUS .... Right, the reserved slots are also initialized with their safe values. However, the macros _PAGE_CACHE_MODE_XXX only refer to the slots specified above. > > + * 111 7 WT : _PAGE_CACHE_MODE_WT > > + */ > > + pat = PAT(0, WB) | PAT(1, WC) | PAT(2, UC_MINUS) | PAT(3, UC) | > > + PAT(4, WB) | PAT(5, WC) | PAT(6, UC_MINUS) | PAT(7, WT); > > + } > > Thanks, Thanks for the review! -Toshi -- 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