From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi0-f47.google.com (mail-oi0-f47.google.com [209.85.218.47]) by kanga.kvack.org (Postfix) with ESMTP id 6C8D19003C7 for ; Tue, 21 Jul 2015 10:53:11 -0400 (EDT) Received: by oigd21 with SMTP id d21so83653708oig.1 for ; Tue, 21 Jul 2015 07:53:11 -0700 (PDT) Received: from g4t3426.houston.hp.com (g4t3426.houston.hp.com. [15.201.208.54]) by mx.google.com with ESMTPS id xj4si18988667oeb.73.2015.07.21.07.53.10 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 21 Jul 2015 07:53:10 -0700 (PDT) Message-ID: <1437490320.3214.206.camel@hp.com> Subject: Re: [PATCH v2 0/4] x86, mm: Handle large PAT bit in pud/pmd interfaces From: Toshi Kani Date: Tue, 21 Jul 2015 08:52:00 -0600 In-Reply-To: <20150721080544.GA28118@gmail.com> References: <1436977435-31826-1-git-send-email-toshi.kani@hp.com> <20150721080544.GA28118@gmail.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: Ingo Molnar Cc: hpa@zytor.com, tglx@linutronix.de, mingo@redhat.com, akpm@linux-foundation.org, bp@alien8.de, linux-mm@kvack.org, linux-kernel@vger.kernel.org, x86@kernel.org, jgross@suse.com, konrad.wilk@oracle.com, elliott@hp.com On Tue, 2015-07-21 at 10:05 +0200, Ingo Molnar wrote: > * Toshi Kani wrote: > > > The PAT bit gets relocated to bit 12 when PUD and PMD mappings are > > used. > > This bit 12, however, is not covered by PTE_FLAGS_MASK, which is > > corrently > > used for masking pfn and flags for all cases. > > > > Patch 1/4-2/4 make changes necessary for patch 3/4 to use > > P?D_PAGE_MASK. > > > > Patch 3/4 fixes pud/pmd interfaces to handle the PAT bit when PUD and > > PMD > > mappings are used. > > > > Patch 3/4 fixes /sys/kernel/debug/kernel_page_tables to show the PAT > > bit > > properly. > > > > Note, the PAT bit is first enabled in 4.2-rc1 with WT mappings. > > Are patches 1-3 only needed to fix /sys/kernel/debug/kernel_page_tables > output, or > are there other things fixed as well? The patches do not tell us any of > that information ... Patch 3 (and patch 1-2 needed for patch 3) fixes multiple pud/pmd interfaces to work properly with _PAGE_PAT_LARGE bit set. Because pmem is the only module that can create a range with this bit set with large page WT maps in 4.2, this issue has not been exposed other than the case in kernel_page_tables fixed by patch 4. Since there can be other cases in future, all patches should go to 4.2 to prevent them to happen. There is no issue in 4.1 & older since they cannot set the bit. Thanks, -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