From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-la0-f49.google.com (mail-la0-f49.google.com [209.85.215.49]) by kanga.kvack.org (Postfix) with ESMTP id 6CB342802FF for ; Thu, 16 Jul 2015 14:47:47 -0400 (EDT) Received: by lagw2 with SMTP id w2so48769973lag.3 for ; Thu, 16 Jul 2015 11:47:46 -0700 (PDT) Received: from forward-corp1g.mail.yandex.net (forward-corp1g.mail.yandex.net. [95.108.253.251]) by mx.google.com with ESMTPS id az11si7697475lab.27.2015.07.16.11.47.44 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 16 Jul 2015 11:47:45 -0700 (PDT) Subject: [PATCH] pagemap: update documentation From: Konstantin Khlebnikov Date: Thu, 16 Jul 2015 21:47:42 +0300 Message-ID: <20150716184742.8858.14639.stgit@buzz> In-Reply-To: <20150714152516.29844.69929.stgit@buzz> References: <20150714152516.29844.69929.stgit@buzz> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: linux-mm@kvack.org, Andrew Morton , Naoya Horiguchi Cc: linux-api@vger.kernel.org, linux-kernel@vger.kernel.org Notes about recent changes. Signed-off-by: Konstantin Khlebnikov --- Documentation/vm/pagemap.txt | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) diff --git a/Documentation/vm/pagemap.txt b/Documentation/vm/pagemap.txt index 3cfbbb333ea1..aab39aa7dd8f 100644 --- a/Documentation/vm/pagemap.txt +++ b/Documentation/vm/pagemap.txt @@ -16,12 +16,17 @@ There are three components to pagemap: * Bits 0-4 swap type if swapped * Bits 5-54 swap offset if swapped * Bit 55 pte is soft-dirty (see Documentation/vm/soft-dirty.txt) - * Bit 56 page exlusively mapped + * Bit 56 page exclusively mapped (since 4.2) * Bits 57-60 zero - * Bit 61 page is file-page or shared-anon + * Bit 61 page is file-page or shared-anon (since 3.5) * Bit 62 page swapped * Bit 63 page present + Since Linux 4.0 only users with the CAP_SYS_ADMIN capability can get PFNs: + for unprivileged users from 4.0 till 4.2 open fails with -EPERM, starting + from from 4.2 PFN field is zeroed if user has no CAP_SYS_ADMIN capability. + Reason: information about PFNs helps in exploiting Rowhammer vulnerability. + If the page is not present but in swap, then the PFN contains an encoding of the swap file number and the page's offset into the swap. Unmapped pages return a null PFN. This allows determining @@ -160,3 +165,8 @@ Other notes: Reading from any of the files will return -EINVAL if you are not starting the read on an 8-byte boundary (e.g., if you sought an odd number of bytes into the file), or if the size of the read is not a multiple of 8 bytes. + +Before Linux 3.11 pagemap bits 55-60 were used for "page-shift" (which is +always 12 at most architectures). Since Linux 3.11 their meaning changes +after first clear of soft-dirty bits. Since Linux 4.2 they are used for +flags unconditionally. -- 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